ABSTRACT OBJETIVE Food intake, energy expenditure, and metabolic homeostasis depend on hypothalamic neurons’ responses to peripheral signals, such as leptin, involving the primary cilium (PC). The PC is crucial for signal transduction and is dynamically regulated by assembly/disassembly or reabsorption of its microtubules-based axoneme. Absence or reduction in the length of PC is associated with obesity and type-2 diabetes (T2D). In other cellular systems, PC reabsorption is primarily regulated by calcium-mediated activation of the Aurora kinase A (AurkA)/histone deacetylase C6 (HDAC6) axis, which promotes axonemal disassembly. Here, we explore the role of Galectin-8 (Gal-8), a glycan-binding protein, in regulating PC structure and signaling related to metabolic parameters in hypothalamic neurons. METHODS Gal-8 effects were assessed in hypothalamic Clu-177 cells by analyzing the PC presence and length by immunofluorescence, PC dynamics, and intracellular calcium changes by in vivo cell imaging, activation of FAK, Src, AurkA, HDAC6 and STAT3 by immunoblot, and Gal-8 interactions with β1-integrins by pull-down assays. Gal-8-KO mice were used to evaluate PC length in hypothalamic neurons, metabolic phenotype, and responses to Gal-8 intranasal administration. RESULTS In Clu-177 cells, Gal-8 induced PC reabsorption and reduced responsiveness to leptin signaling towards STAT3 activation. PC reabsorption involves glycan-mediated Gal-8 interactions with a5b1 and a3b1 integrins, activation of FAK and Src leading to calcium influx through L-type calcium channels (LTCC), and subsequent AurkA/HDAC6 axis activation. Gal-8-KO mice showed longer PC in hypothalamic neurons, higher STAT3 activation, decreased body weight and food intake, improved glucose tolerance, higher locomotor activity, and a glycolytic respiratory exchange rate (RER). Daily intranasal Gal-8 administration for 4 days restored hypothalamic PC length and STAT3 signaling, as well as RER in Gal-8-KO mice to the level of WT mice. CONCLUSIONS Endogenous Gal-8 is required to maintain PC structure and leptin signaling in hypothalamic neurons, impacting body weight, energy balance, and glucose homeostasis. The mechanism involves calcium influx via LTCC downstream of b1-integrin/FAK/Src signaling and subsequent AurkA/HDAC6 axis activation. Both Gal-8 and the AurkA/HDAC6 axis may offer new therapeutic opportunities for treating metabolic diseases characterized by ciliogenesis impairment, including obesity and type-2 diabetes.

Dyslipidemia, characterized by an excessive amount of lipids in the bloodstream, is a significant risk factor for metabolic disorders and cardiovascular diseases (CVDs). Maternal supraphysiological hypercholesterolemia (MSPH) is associated with increased maternal levels of total cholesterol (TC) and low-density lipoprotein (LDL). This condition has been linked to negative consequences on the fetoplacental vasculature, including increased atherosclerosis development in the fetal aorta and later in children and adolescents. This study aims to determine whether the high cholesterol levels associated with MSPH affect lysosomal and mitochondrial functions in the syncytiotrophoblast (STB), considering the increased free cholesterol levels previously reported in primary human trophoblast (PHT) cells from MSPH pregnancies. Total cholesterol levels were measured in placental tissues and BeWo cells. Lysosomal mass, size, and activity, as well as mitochondrial mass, function, and morphology, were assessed in BeWo cells and placentas. Our results revealed that placental tissues from MSPH pregnancies and BeWo cells treated with oxidized (ox-LDL) exhibited increased free cholesterol levels and higher expression of cholesterol transport proteins. Treatment of BeWo cells with ox-LDL also led to an increase in lysosomal mass and size, accompanied by a decrease in lysosomal activity. Conversely, ox-LDL treatment induced mitochondrial fragmentation in BeWo cells, together with reduced ATP production and diminished mitochondrial membrane potential. Similar alterations in lysosomes and mitochondria were observed in the placenta of patients with a history of MSPH. MSPH-related high cholesterol levels induced by ox-LDL impair lysosomal and mitochondrial functions in the STB, potentially contributing to cellular dysfunction observed in MSPH. This study highlights the importance of understanding the underlying mechanisms of MSPH to improve maternal and fetal health outcomes.

Aging is a natural and progressive biological process characterized by morphological, physiological, and metabolic changes that occur over time. It is the most substantial risk factor for cognitive decline and neurodegenerative disorders. Mitochondrial dysfunction is a central driver of hippocampal synaptic failure and memory impairment during aging. Red630nm-Light Transcranial LED therapy (RL-TCLT) is an innovative and non-invasive photobiomodulation strategy that uses a 630 nm wavelength to deliver photons that activate sensitive molecules within brain cells, thereby promoting neurotherapeutic effects and providing tissue therapy for neurological conditions. However, its cellular targets and relevance for age-associated cognitive decline remain poorly understood. Here, we investigated the impact of chronic RL-TCLT on hippocampal mitochondrial function, synaptic integrity, neurogenesis, and memory in 7-month-old Senescence-Accelerated Mouse-Prone 8 (SAMP8) mice. Daily RL-TCLT (125 s/day for 5 weeks) robustly enhanced mitochondrial bioenergetics function in the hippocampus, as evidenced by increased oxygen consumption, ATP production, and cytochrome c oxidase activity, accompanied by reduced reactive oxygen species generation and improved resistance to calcium overload. At the synaptic level, RL-TCLT increased synaptic protein abundance, promoted mushroom-type spine formation, enhanced dendritic arborization, and significantly improved hippocampal-dependent spatial memory. Notably, these effects occurred independently of adult hippocampal neurogenesis, as neither proliferation (Ki67⁺) nor neuronal differentiation (DCX⁺) in the dentate gyrus was altered. Therefore, our findings identify mitochondrial activation as a primary cellular target of RL-TCLT in the aging hippocampus and demonstrate that enhancement of synaptic structure and function can be achieved without engaging neurogenesis. This work uncovers a previously unrecognized mechanism by which photobiomodulation preserves hippocampal circuitry and cognitive function, positioning RL-TCLT as a promising non-invasive strategy to counteract age-related synaptic and memory decline.

The hippocampus is crucial to learning and memory, functions that decline with age due to impaired mitochondrial bioenergetics and reduced mitophagy, resulting in the accumulation of dysfunctional mitochondria and increased susceptibility to neurodegeneration. Urolithin A (UA), a natural mitophagy activator derived from polyphenols, has demonstrated benefits in Alzheimer’s disease models; however, its role in normal aging remains unclear. Here, we investigated whether UA can prevent or reverse hippocampal dysfunction by enhancing mitophagy and mitochondrial function. Two mouse models were used: 18-month-old C57BL/6 mice with established mitochondrial and cognitive deficits, and 5-month-old SAMP8 mice, an accelerated aging with cognitive decline starting from 6 months of age. UA was administered for 8 weeks, followed by assessments of ATP production, mitochondrial dynamics, mitophagy markers, synaptic proteins, and memory. In C57BL/6 mice, UA increased ATP, boosted proteins associated with fusion, antioxidant defense, and biogenesis, and reduced phosphorylated tau; however, these changes did not restore memory. In contrast, SAMP8 mice showed stronger effects: ATP rose sharply, mitochondrial stress and aberrant proteins decreased, and cognitive performance improved. These findings highlight UA effects as a preventive therapeutic agent, but are insufficient to reverse established cognitive decline, suggesting early mitophagy activation is critical to mitigate brain aging and neurodegeneration.

Current evidence indicates that Parkinson's disease (PD) involves T cell-mediated inflammation, which plays a fundamental role in promoting neuroinflammation and neurodegeneration in patients and animal models. These T cells are specific to α-synuclein-derived antigens, including nitrated α-synuclein (NαSyn). Here, we sought to develop an experimental immunotherapy for PD based on the generation of regulatory T cells (Treg) specific to NαSyn, using the chimeric antigen receptor (CAR) technology. Accordingly, we first obtained an antibody specific to human α-synuclein containing three nitrated tyrosine residues (3NY-hαSyn), which displayed specific immunoreactivity in the serum of PD patients which correlated with the clinical score. Afterward, we generated CAR-Treg specific to 3NY-hαSyn and tested them in two PD models involving human α-synuclein. The CAR-Treg therapy substantially inhibited the inflammatory T cell response specific to α-synuclein-derived antigens, neuroinflammation, neurodegeneration, and the motor decline. This preclinical study indicates that the CAR-Treg therapy represents a promising therapeutic strategy for treating PD patients.

Lonp1 is the main mitochondrial matrix protease responsible for maintaining mitochondrial proteostasis through the degradation of damaged or misfolded proteins. Although impaired Lonp1 expression or activity has been linked to mitochondrial dysfunction and oxidative stress in peripheral tissues and non-neuronal cells, its role in the brain, and particularly in hippocampal function, remains unexplored. Here, we provide the first in vivo evidence that Lonp1 activity is a critical regulator of mitochondrial redox homeostasis, synaptic integrity, and learning in the hippocampus. We administered the Lonp1 inhibitor Sesamin intranasally to 4-month-old adult Senescent-Acelerated Mouse Prone 8 (SAMP8) mice for 6 weeks. Subsequently, we conducted cognitive tests to assess hippocampal-dependent learning and memory. We also examined Lonp1 proteolytic activity using the FITC-Casein assay, performed Golgi staining to evaluate dendritic spines, and used fluorescent and luminescent probes to investigate mitochondrial function. Interestingly, we selectively impaired Lonp1 function at an early stage of age-related brain vulnerability. Lonp1 inhibition led to the accumulation of mitochondrial Lonp1 substrates and a marked reduction in mitochondrial bioenergetic capacity, as reflected by decreased ATP production and a robust increase in mitochondrial reactive oxygen species (ROS). These redox alterations were accompanied by selective synaptic remodeling, characterized by a reduction in thin dendritic spines without changes in total spine density, and by impaired hippocampus-dependent learning, while memory retention remained preserved. Thus, our findings identify Lonp1 as a previously unrecognized regulator of mitochondrial redox balance and synaptic structure in the hippocampus. Importantly, Lonp1 inhibition recapitulates key features of brain aging, linking defective mitochondrial proteostasis to ROS-driven synaptic vulnerability and cognitive dysfunction. This study establishes Lonp1-dependent mitochondrial quality control as a central node connecting redox dysregulation to synaptic failure and highlights Lonp1 as a novel target for strategies aimed at preserving mitochondrial and cognitive function during aging.

OBJECTIVE:The neuroepigenetic factor Mecp2 regulates gene expression and is thought to play a crucial role in energy homeostasis. Body weight is regulated at the hypothalamic level, where mitochondrial energy metabolism is necessary for its proper functioning, allowing the hypothalamus to respond to peripheral signals to maintain energy balance and modulate energy expenditure through the sympathetic nervous system. Since the mechanism by which genetic and environmental factors contribute to regulating energy balance is unclear, this study aims to understand the contribution of gene-environment interaction to maintaining energy balance and how its disruption alters hypothalamic cellular energy production, impacting the control of systemic metabolism. METHODS:We used a mouse model of epigenetic disruption (Mecp2-null) to evaluate the impact of Mecp2 deletion on systemic and hypothalamic metabolism using physiological and cellular approaches. RESULTS:Our study shows that the previously reported body weight gain in mice lacking the expression of Mecp2 is preceded by a hypothalamic mitochondrial dysfunction that disrupts hypothalamic function, leading to a dysfunctional communication between the hypothalamus and adipose tissue, thus impairing lipid metabolism. Our study has revealed three crucial aspects of the contribution of this critical epigenetic factor pivotal for a proper gene-environment interaction: i) Mecp2 drives a molecular mechanism to maintain cellular energy homeostasis, which is necessary for the proper functioning of the hypothalamus. ii) Mecp2 is necessary to maintain lipid metabolism in adipose tissue. iii) Mecp2 is a molecular bridge linking hypothalamic cellular energy metabolism and adipose tissue lipid metabolism. CONCLUSIONS:Our results show that Mecp2 regulates the hypothalamic mitochondrial function and white adipose tissue lipid metabolism and probably alters the communication between these two tissues, which is critical for corporal energy homeostasis maintenance.

Aging is a physiological and complex process produced by accumulative age-dependent cellular damage, which significantly impacts brain regions like the hippocampus, an essential region involved in memory and learning. A crucial factor contributing to this decline is the dysfunction of mitochondria, particularly those located at synapses. Synaptic mitochondria are specialized organelles that produce the energy required for synaptic transmission but are also important for calcium homeostasis at these sites. In contrast, non-synaptic mitochondria primarily involve cellular metabolism and long-term energy supply. Both pools of mitochondria differ in their form, proteome, functionality, and cellular role. The proper functioning of synaptic mitochondria depends on processes such as mitochondrial dynamics, transport, and quality control. However, synaptic mitochondria are particularly vulnerable to age-associated damage, characterized by oxidative stress, impaired energy production, and calcium dysregulation. These changes compromise synaptic transmission, reducing synaptic activity and cognitive decline during aging. In the context of neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's, the decline of synaptic mitochondrial function is even more pronounced. These diseases are marked by pathological protein accumulation, disrupted mitochondrial dynamics, and heightened oxidative stress, accelerating synaptic dysfunction and neuronal loss. Due to their specialized role and location, synaptic mitochondria are among the first organelles to exhibit dysfunction, underscoring their critical role in disease progression. This review delves into the main differences at structural and functional levels between synaptic and non-synaptic mitochondria, emphasizing the vulnerability of synaptic mitochondria to the aging process and neurodegeneration. These approaches highlight the potential of targeting synaptic mitochondria to mitigate age-associated cognitive impairment and synaptic degeneration. This review emphasizes the distinct vulnerabilities of hippocampal synaptic mitochondria, highlighting their essential role in sustaining brain function throughout life and their promise as therapeutic targets for safeguarding the cognitive capacities of people of advanced age.

Obesity is a global public health challenge emerging from an energy homeostasis (EO) disruption. EO is primarily driven by neurons residing in the hypothalamus, whose function is critical to integrate neural and humoral signals that account for energy balance. Obesogenic diets induce a loss of function in the mechanism through which these neurons sense the energy status, leading to the systemic accumulation of excess energy. This could result from altered cellular EO involving mitochondria and molecular energy sensors, such as AMP‐activated protein kinase (AMPK) and/or K ATP channels. In this line, hyperglycemia induced by obesogenic diets alters the central regulation of energy balance in the hypothalamus, possibly due to the loss of sensing anorexigenic signals induced by hyperinsulinemia and hyperleptinemia, mediated by deficient energy control involving mitochondria, AMPK, and K ATP channels. Therefore, reducing elevated glycemia in a mouse model of hypercaloric feeding could restore cellular energy sensing and normalize energy homeostasis. To test this hypothesis, this work aims to evaluate whether the loss of body energy balance induced by hypercaloric 45% high‐fat diet (D45%) feeding is prevented by oral hypoglycemiant, metformin (MT), by restoring mitochondrial function, AMPK sensitivity, and K ATP levels in the hypothalamus of mice. For this purpose, mice were fed a D45% and supplemented with MT for 12 weeks. Metabolic, physiological, and molecular parameters were assessed. The treatment with MT decreased food intake and body weight gain induced by D45% feeding; besides, MT increased horizontal locomotor activity and attenuated insulin resistance and glucose intolerance after 12 weeks of treatment. Regarding energy sensors, MT attenuated the increased phosphorylation of AMPK and reduced the expression of Kir6.2 induced by D45% feeding. These results show that reduced glycemia can partially reverse the decreased energy sensor function and the altered energy metabolism induced by feeding with a hypercaloric diet.

Anti-ribosomal P protein autoantibodies (anti-P) are associated with psychosis and cognitive dysfunction in patients with systemic lupus erythematosus (SLE), yet the underlying mechanisms remain undefined, hindering targeted therapies. Anti-P cross-react with a neuronal surface protein (NSPA), alter glutamatergic synaptic transmission and plasticity in hippocampal slices, and impair spatial memory in a short-term passive transfer mouse model. NSPA knockout mice display spatial memory deficit linked to reduced NMDAR activity and postsynaptic density (PSD) levels, along with an increased membrane-associated tyrosine phosphatase PTPMEG, suggesting disrupted glutamatergic receptor trafficking. Here, we investigated the acute effects of anti-P on receptor cell surface expression and trafficking in cultured hippocampal neurons and their long-term impact on hippocampal components and spatial memory in anti-P( +) immunized mice. NMDAR and AMPAR surface expression and NMDAR recycling were assessed in 21-24 DIV primary hippocampal neurons by immunofluorescence and FRAP using SEP-tagged receptors under the effects of rabbit anti-P IgG fractions. In vivo, female C57BL/6 mice were immunized with recombinant P0 ribosomal protein to induce anti-P, followed by lipopolysaccharide (LPS) intraperitoneal administration to breach the blood-brain-barrier (BBB). Spatial memory was evaluated with a water maze memory flexibility test. Hippocampal synaptosomal membranes and PSD-enriched fractions were analyzed by immunoblotting. Neuronal density, microglia and dendritic architecture were evaluated using Cresyl Violet, Iba1 and Golgi staining, respectively. Anti-P treatment of cultured neurons reduced GluN2A and GluA1 surface levels and impaired SEP-GluN2A and SEP-GluN2B recycling. Anti-P( +) mice showed spatial memory deficits persisting up to 24 days post-LPS, along with hippocampal alterations that include reduced levels of NMDAR, AMPAR, and PSD-95 in PSD fractions; increased membrane-associated PTPMEG; 7

Aging is characterized by a progressive decline in cellular function, including the hippocampus, a brain region crucial for learning and memory. Mitochondrial dysfunction is a hallmark of aging, critical for hippocampal deterioration. The mitochondrial protease Lonp1 is a key regulator of mitochondrial proteostasis, and its diminished expression or activity has been implicated in age-related dysfunction in non-neuronal cells. However, despite its essential role in maintaining mitochondrial function, the transcriptional regulation of Lonp1 remains poorly understood. Evidence suggests that Lonp1 is subject to epigenetic control via changes in DNA methylation patterns. Mepc2, a DNA-methylation reader, acts as a transcriptional regulator highly expressed in neurons, either activating or repressing gene expression. Yet, its role in the mitochondria of aged hippocampus and its potential role as Lonp1 regulator haven’t been explored. Here, we investigated Lonp1 expression and its epigenetic regulation by Mecp2 in the hippocampus of aged SAMP8 mice. We identified CpG islands in the Lonp1 promoter, near the transcription start site, where DNA methylation levels increase in aged hippocampal tissue. Chromatin immunoprecipitation revealed that Mecp2 directly binds to the Lonp1 promoter, with a significant reduction in binding observed in aged mice, correlating with increased Lonp1 mRNA levels. These findings show, for the first time, that Mecp2 is a transcriptional repressor of Lonp1 in the hippocampus. Additionally, unlike humans expressing three isoforms of Lonp1, mice exhibit only the full-length mitochondrial isoform. Interestingly, despite increased Lonp1 mRNA levels in aged mice, their protein levels were significantly decreased in the aged hippocampus. This unexpected result is, at least in part, explained by the enhanced Lonp1 protein degradation by the lysosome. Together, our findings reveal a novel mechanism that drives Lonp1 expression, linking Mecp2-mediated epigenetic regulation to age-related mitochondrial dysfunction. This study reveals Mecp2 and Lonp1 as potential therapeutic targets for mitochondrial proteostasis in aging.

Background Dietary sugars, particularly fructose, are increasingly implicated in cancer progression through their impact on tumor metabolism. However, the specific metabolic adaptations driven by fructose in prostate cancer (PCa) remain unexplored. Methods We investigated the metabolic consequences of chronic fructose exposure in androgen-sensitive (LNCaP) and androgen-independent (PC-3) PCa cell lines. We evaluated the expression, localization, and function of the fructose transporter Glut-5 and assessed metabolic fluxes, enzyme expression, lipid accumulation, and global metabolite profiles using molecular, imaging, and metabolomic approaches. Results Glut-5 was primarily localized to early endosomes under basal and fructose-stimulated conditions, suggesting a non-canonical role potentially consistent with transceptor function. Chronic fructose exposure significantly upregulated Glut-5 expression and enhanced fructose uptake, but did not alter substantially its subcellular localization. Functionally, fructose reduced lactate production and mitochondrial ATP output, indicating a metabolic shift away from glycolysis and oxidative phosphorylation. In LNCaP cells, fructose induced robust activation of de novo lipogenesis (DNL), evidenced by upregulation of FASN and G6PD, increased lipid droplet accumulation, and enhanced levels of key fatty acid metabolites (e.g., TG, EPA, DHA). In contrast, PC-3 cells exhibited a distinct metabolic response, characterized by increased ceramide and amino acid metabolites. Notably, pharmacological inhibition of lipid metabolism using etomoxir abrogated proliferation in both cell lines under fructose stimulation. Conclusions These findings reveal that fructose promotes a metabolic reprogramming in PCa cells that is cell type- and AR-dependent, enhancing lipogenesis and potentially contributing to tumor progression. Our study identifies Glut-5–mediated fructolysis and lipid metabolic pathways as key vulnerabilities in PCa, offering potential avenues for metabolic intervention. ### Competing Interest Statement The authors have declared no competing interest. Fondecyt, 1221067 PhD national fellowship ANID-Chile, 21210701

Mitochondria produces energy through oxidative phosphorylation (OXPHOS), maintaining calcium homeostasis, survival/death cell signaling mechanisms, and redox balance. These mitochondrial functions are especially critical for neurons. The hippocampus is crucial for memory formation in the brain, which is a process with high mitochondrial function demand. Loss of hippocampal function in aging is related to neuronal damage, where mitochondrial impairment is critical. Synaptic and mitochondrial dysfunction are early events in aging; both are regulated reciprocally and contribute to age-associated memory loss together. We previously showed that prolonged treatment with Curcumin or Mitoquinone (MitoQ) improves mitochondrial functions in aged mice, exerting similar neuroprotective effects. Curcumin has been described as an anti-inflammatory and antioxidant compound, and MitoQ is a potent antioxidant directly targeting mitochondria; however, whether Curcumin exerts a direct impact on the mitochondria is unclear. In this work, we study whether Curcumin could have a mechanism similar to MitoQ targeting the mitochondria. We utilized hippocampal slices of 4-6-month-old C57BL6 mice to assess the cellular changes induced by acute Curcumin treatment ex-vivo compared to MitoQ. Our results strongly suggest that both compounds improve the synaptic structure, oxidative state, and energy production in the hippocampus. Nevertheless, Curcumin and MitoQ modify mitochondrial function differently; MitoQ improves the mitochondrial bioenergetics state, reducing ROS production and increasing ATP generation. In contrast, Curcumin reduces mitochondrial calcium levels and prevents calcium overload related to mitochondrial swelling. Thus, Curcumin is described as a new regulator of mitochondrial calcium homeostasis and could be used in pathological events involving calcium deregulation and excitotoxicity, such as aging and neurodegenerative diseases.

Aging is a progressive process characterized by cellular and molecular damage leading to mitochondrial dysfunction and cognitive decline. Mitochondrial dysfunction is a critical factor in memory impairment in aging and neurodegenerative diseases. While sex differences in aging have been observed across various species, the underlying cellular and molecular mechanisms remain poorly understood, mainly focused on mitochondrial proteostasis. This study examined hippocampal-dependent cognitive decline and mitochondrial dysfunction in aged male and female C57BL/6 J mice. Our results reveal sex-dependent differences in cognitive impairment, with aged males exhibiting more significant deficits in spatial and localization memory, while aged females show impairments in recognition memory. Additionally, aged males display increased oxidative stress and exacerbated mitochondrial superoxide production, leading to more severe bioenergetic deficiencies. Conversely, aged females exhibit heightened mitochondrial permeability transition pore (mPTP) activity, suggesting a distinct mechanism of mitochondrial dysfunction, which could explain, almost in part, the cognitive differences in aging. Investigating possible mechanisms responsible for this mitochondrial dysfunction, we found that mitochondrial proteostasis is more prone to failure in aged males, with a significant decrease in the protease activity of Lonp1, a key matrix mitochondrial protease degrading >50% of the mitochondrial proteome. To further reinforce these findings, we replicated key experiments in SAMP8 mice, a model of accelerated aging, obtaining consistent results that strengthen the robustness and generalization of our conclusions. These findings suggest that sex influences hippocampal aging at multiple levels, highlighting the need to consider sexual dimorphism in aging research. This study also emphasizes the critical role of mitochondrial proteostasis in maintaining mitochondrial function in aging in a sex-dependent manner. Understanding these differences could facilitate the development of sex-specific strategies to mitigate age-related cognitive decline and neurodegeneration.

The integrated stress response (ISR) modulates protein homeostasis in response to both intracellular and extracellular signals. The four kinases involved in the ISR all phosphorylate the same target, the alpha subunit of eukaryotic initiation factor 2 (eIF2α), to integrate various stress signals, thereby regulating cell fate. The activation of the ISR reprograms the proteome by inhibiting general protein synthesis while increasing the translation of specific mRNAs. In the brain, the ISR regulates the type of synaptic plasticity necessary for forming long-term memory. More importantly, the activation of the ISR has emerged as a causal mechanism underlying cognitive decline associated with a wide range of neurological disorders, prompting several pharmaceutical companies to target the ISR to promote brain health. However, whether the ISR acts at specific localities within neurons, including synapses, remains unclear. Here, we examined the presence, activity, and spatial arrangement of the ISR branch driven by the double-stranded RNA-dependent protein kinase (PKR) (PKR-eIF2α axis) in synapses and assessed the role of PKR in maintaining synaptic proteostasis over time. Our findings demonstrate that both PKR and eIF2α are localized at synapses, where a dynamic PKR-eIF2α axis regulates synaptic size and the abundance of synaptic proteins in an age-dependent manner. Moreover, PKR deficiency leads to an increase in protein synthesis in synapse-enriched fractions. Thus, the PKR branch of the ISR serves as a new regulator of synaptic structural plasticity.

Background/Objectives: Aging has been extensively studied, with a growing interest in memory impairment by a neurobiological approach. Mitochondrial dysfunction is a hallmark of aging, contributing to the aging phenotype; therefore, mitochondrial interventions seem fundamental. The diet is a physiological approximation for modifying mitochondria, which could impact the age-related phenotype. Methods: We studied two diets with low-carbohydrate and high-fat compositions, differing in the amount of protein and the fat type disposable—the atherogenic diet Cocoa (high protein/high saturated fat/high cholesterol) and the South Beach diet (very high-protein/high-unsaturated fat)—on oxidative stress, mitochondrial state, and hippocampus-dependent memory in 3-month-old Senescence-Accelerated Mouse Model (SAMP8) seed over 3 months to determine their pro- or anti-aging effects. Results: Despite its bad reputation, the Cocoa diet reduces the reactive oxygen species (ROS) content without impacting the energy state and hippocampus-dependent spatial acuity. In contrast to the beneficial impact proposed for the South Beach diet, it induced a pro-aging phenotype, increasing oxidative damage and the levels of NR2B subunit of the NMDA, impairing energy and spatial acuity. Surprisingly, despite the negative changes observed with both diets, this led to subtle memory impairment, suggesting the activation of compensatory mechanisms preventing more severe cognitive decline. Conclusions: Our results demonstrated that diets usually considered good could be detrimental to the onset of aging. Also, probably due to the brain plasticity of non-aged animals, they compensate for the damage, preventing a more aggravated phenotype. Nevertheless, these silent changes could predispose or increase the risk of suffering pathologies at advanced age.

Aging is a multifaceted biological process characterized by progressive molecular and cellular damage accumulation. The brain hippocampus undergoes functional deterioration with age, caused by cellular deficits, decreased synaptic communication, and neuronal death, ultimately leading to memory impairment. One of the factors contributing to this dysfunction is the loss of mitochondrial function. In neurons, mitochondria are categorized into synaptic and non-synaptic pools based on their location. Synaptic mitochondria, situated at the synapses, play a crucial role in maintaining neuronal function and synaptic plasticity, whereas non-synaptic mitochondria are distributed throughout other neuronal compartments, supporting overall cellular metabolism and energy supply. The proper function of synaptic mitochondria is essential for synaptic transmission as they provide the energy required and regulate calcium homeostasis at the communication sites between neurons. Maintaining the structure and functionality of synaptic mitochondria involves intricate processes, including mitochondrial dynamics such as fission, fusion, transport, and quality control mechanisms. These processes ensure that mitochondria remain functional, replace damaged organelles, and sustain cellular homeostasis at synapses. Notably, deficiencies in these mechanisms have been increasingly associated with aging and the onset of age-related neurodegenerative diseases. Synaptic mitochondria from the hippocampus are particularly vulnerable to age-related changes, including alterations in morphology and a decline in functionality, which significantly contribute to decreased synaptic activity during aging. This review comprehensively explores the critical roles that mitochondrial dynamics and quality control mechanisms play in preserving synaptic activity and neuronal function. It emphasizes the emerging evidence linking the deterioration of synaptic mitochondria to the aging process and the development of neurodegenerative diseases, highlighting the importance of these organelles from hippocampal neurons as potential therapeutic targets for mitigating cognitive decline and synaptic degeneration associated with aging. The novelty of this review lies in its focus on the unique vulnerability of hippocampal synaptic mitochondria to aging, underscoring their importance in maintaining brain function across the lifespan.

Wnt signaling plays a role in synaptic plasticity, but the specific cellular events and molecular components involved in Wnt signaling-mediated synaptic plasticity are not well defined. Here, we report a change in the threshold required to induce synaptic plasticity that facilitates the induction of long-term potentiation (LTP) and inhibits the induction of long-term depression (LTD) during brief exposure to the noncanonical ligand Wnt-5a. Both effects are related to the metaplastic switch of hippocampal CA3-CA1 synaptic transmission, a complex mechanism underlying the regulation of the threshold required to induce synaptic plasticity and of synaptic efficacy. We observed an early increase in the amplitude of field excitatory postsynaptic potentials (fEPSPs) that persisted over time, including after washout. The first phase involves an increase in the fEPSP amplitude that is required to trigger a spontaneous second phase that depends on Jun N-terminal kinase (JNK) and N-methyl D-aspartate receptor (NMDAR) activity. These changes are prevented by treatment with secreted frizzled-related protein 2 (sFRP-2), an endogenous antagonist of Wnt ligands. Here, we demonstrate the contribution of Wnt-5a signaling to a process associated with metaplasticity at CA3-CA1 synapses that favors LTP over LTD.

In this study, we investigated the inter-organelle communication between the Golgi apparatus (GA) and mitochondria. Previous observations suggest that GA-derived vesicles containing phosphatidylinositol 4-phosphate (PI(4)P) play a role in mitochondrial fission, colocalizing with DRP1, a key protein in this process. However, the functions of these vesicles and potentially associated proteins remain unknown. GOLPH3, a PI(4)P-interacting GA protein, is elevated in various types of solid tumors, including breast cancer, yet its precise role is unclear. Interestingly, GOLPH3 levels influence mitochondrial mass by affecting cardiolipin synthesis, an exclusive mitochondrial lipid. However, the mechanism by which GOLPH3 influences mitochondria is not fully understood. Our live-cell imaging analysis showed GFP-GOLPH3 associating with PI(4)P vesicles colocalizing with YFP-DRP1 at mitochondrial fission sites. We tested the functional significance of these observations with GOLPH3 knockout in MDA-MB-231 cells of breast cancer, resulting in a fragmented mitochondrial network and reduced bioenergetic function, including decreased mitochondrial ATP production, mitochondrial membrane potential, and oxygen consumption. Our findings suggest a potential negative regulatory role for GOLPH3 in mitochondrial fission, impacting mitochondrial function and providing insights into GA–mitochondria communication.