The basic helix-loop-helix transcription factor neuronal PAS (Per, Arnt, Sim) domain protein 3 (NPAS3) provides transcriptional regulation of metabolic pathways and is highly expressed in astrocytes. NPAS3 variants have been associated with cognitive dysfunction under several neuropsychiatric conditions, but the underlying brain cell type-specific mechanisms remain obscure. Here, we report that NPAS3 is a key regulator of mitochondrial bioenergetics in astrocytes in the mouse brain. Selective deletion of Npas3 in mature astrocytes decreases expression of mitochondrial glutamate carrier 2 involved in glutamate oxidation, leading to reduced oxidative phosphorylation and lactate production in astrocytes. This deficit reduces intrinsic excitability, dendritic spine density, and excitatory synaptic transmission of medial prefrontal cortex (mPFC) pyramidal neurons. Mice with Npas3-deficient mPFC astrocytes exhibit impaired trace fear conditioning, which is rescued by lactate treatment. Thus, the present study demonstrates a mechanistic link between NPAS3-dependent astrocyte mitochondrial bioenergetics and cognitive function and provides insights for glia-targeting treatment of cognitive dysfunction in neuropsychiatric disease.

Whole brain radiotherapy (WBRT) prolongs survival for patients with brain metastases but produces persistent oxidative injury to the brain and long-term neuropsychiatric sequelae, for which no approved neuroprotective therapies exist. Here, we show that a single course of WBRT produces chronic oxidative stress in mice that persists for at least one year, equivalent to decades in humans, and selectively injures the hippocampus, causing cognitive decline and depressive-like behavior. Daily administration of P7C3-A20, a neuroprotective compound that stabilizes brain nicotinamide adenine dinucleotide (NAD+) homeostasis, markedly reduced oxidative stress and prevented hippocampal pathology for one year after WBRT. P7C3-A20 treatment suppressed neuroinflammation, axonal injury, loss of hippocampal neural precursor cells, blood-brain barrier breakdown, and microglial lipid droplet accumulation, resulting in long-term preservation of cognition and brain health. Crucially, P7C3-A20 did not impair the antitumor efficacy of radiation. These findings identify NAD+ homeostasis stabilization as a promising strategy to mitigate radiation-induced oxidative damage and to prevent long-term neuropsychiatric complications of WBRT.

Repurposing existing medicines to target disease-associated genes represents a promising strategy for developing effective treatments for complex diseases. However, progress has been hindered by a lack of viable candidate drug targets identified through genome-wide association studies. Gene-based association tests provide a more powerful alternative to traditional SNP-based methods, yet current approaches often fail to leverage shared heritability across populations and to effectively integrate functional genomic data. To address these challenges, we develop GenT and its various extensions, comprising a framework of gene-based tests utilizing summary-level data from genome-wide association studies. Using GenT, we identify 16, 15, 35, and 83 candidate genes linked to Alzheimer's disease, amyotrophic lateral sclerosis, major depression, and schizophrenia, respectively, not detected by Genome-Wide Association Studies (GWAS). Additionally, we use our multi-ancestry gene-based test (MuGenT) to identify 28 candidate genes associated with type 2 diabetes. By integrating brain expression and protein quantitative trait loci into our analysis, we identify 43 candidate genes associated with Alzheimer's disease that have supporting xQTL evidence. We also perform experimental assays to demonstrate that the NTRK1 inhibitor GW441756 significantly reduces tau hyper-phosphorylation (including p-tau181 and p-tau217) in Alzheimer's disease patient-derived iPSC neurons, providing mechanistic support for our predictions.

Neuroinflammation is a major secondary driver of Alzheimer's disease (AD). In this issue of Cell Chemical Biology, Carnevale et al.1 demonstrate that S-nitrosylation of the cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING) pathway sustains pathological neuroinflammation in AD, identifying a promising therapeutic target for this devastating disease.

Alzheimer's disease (AD) is characterized by cognitive decline and systemic frailty, but mechanisms linking brain dysfunction to organismal wasting remain unclear. We identify PTPRD, a human-genetically supported regulator of tau pathology, as a high-affinity receptor for amyloid-β (Aβ). Aβ competitively binds the PTPRD extracellular domain, opposing the endogenous ligand asprosin and producing a state of functional signaling insufficiency despite preserved receptor and ligand levels. Circuit-specific Ptprd deletion reveals anatomically distinct memory domains, while increasing asprosin in two AD mouse models restores Ptprd signaling and improves memory in a stage- and circuit-dependent manner. In advanced disease, asprosin supplementation substantially improves weight loss, muscle atrophy, strength, endurance and frailty. These findings support a model in which Aβ disrupts a CNS metabolic signaling axis linking cognition and systemic physiology and suggest that restoring ligand-receptor balance at PTPRD may ameliorate key features of AD.

Deterioration of the blood-brain barrier (BBB), including impaired neurovascular uncoupling, contributes to cognitive decline in aging. The BBB is formed principally by brain microvascular endothelial cells (ECs), and ECs throughout the body are enriched for the transcription factor Krüppel-like factor 4 (KLF4). Because KLF4 levels in ECs decrease with age, we tested whether that decline contributes to aging-related BBB deterioration, neurovascular dysfunction, and cognitive impairment. Using EC-specific Klf4 knockout mice (EC-K4KO), we show that loss of EC KLF4 accelerates multiple age-related brain pathologies. Indeed, middle-aged EC-K4KO mice display pathological features that are not normally observed until advanced age, including marked BBB leakage, impaired neurovascular coupling, loss of microvessels, increased oxidative damage, neuroinflammation, neurodegeneration, anxiety-like behavior, and cognitive deficits. Single-cell RNA sequencing of brain vasculature reveals dysregulation of immune response and barrier-related genes in ECs lacking KLF4, indicating that KLF4 maintains brain endothelial homeostasis by constraining proinflammatory and senescence programs at the chromatin level. Together, these results identify loss of EC KLF4 as a key driver of neurovascular decline and age-associated cognitive dysfunction.

Cellular homeostasis relies on regulation of processes, including protein post-translational modifications (PTMs) and biomolecular condensation. Aging disrupts the equilibrium of these processes, increasing susceptibility to disease and mortality. Here we used chemoproteomic techniques to generate an atlas of cysteine PTMs in the mouse brain and showed that age-related increases in thiol oxidation promoted the formation of biomolecular condensates. By contrast, protein persulfidation, regulated by hydrogen sulfide production, inhibited biomolecular condensation, preserving protein function. Age-induced alterations in cysteine PTMs influenced the phase separation properties of synapsin 1 and G3BP2, leading to impaired neurotransmitter release and defective stress granule formation and resolution, features associated with aging and neurodegenerative diseases. Mice deficient in cystathionine γ-lyase, the enzyme responsible for hydrogen sulfide production, exhibited reduced lifespans and spontaneously developed protein aggregates with age. Our results highlight the therapeutic potential of protein persulfidation in reversal of dysregulated biomolecular condensation and suggest that sulfide donors could be used to mitigate age-related diseases.

Alzheimer's disease (AD) is a complex and poorly understood neurodegenerative disorder that lacks sufficiently effective treatments. Computational and integrative analyses that leverage multiomic data provide a promising strategy to uncover disease mechanisms and identify therapeutic opportunities. Here, we develop a cell type-specific regulatory atlas of the human middle temporal gyrus via leveraging single-nucleus RNA-seq (1,197,032 nuclei) and ATAC-seq (740,875 nuclei) data sets from 84 donors across four stages of AD neuropathological change (ADNC). We observe differential gene expression for six major cell types intensified at severe ADNC. Integrating peak-to-gene linkages and motif enrichment analyses, we reconstruct transcription factor (TF)-target gene networks across six major brain cell types. By integrating genome-wide association study (GWAS) loci with cell type-specific cis-regulatory DNA elements (CREs), we pinpoint 141 ADNC-associated genes. Using gene set enrichment analysis (GSEA) and network proximity analysis, we further identify nine candidate repurposable drugs that were associated with these ADNC-related genes. In summary, this cell type-specific multiomic atlas provides a comprehensive resource for mechanistic understanding, target prioritization, and therapeutic hypothesis generation in AD and AD-related dementia if broadly applied.

The prostaglandin- and autocoid-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH) is shown here to be pathologically elevated in Parkinson's disease (PD) patients and mouse models of PD in the substantia nigra, the region of the brain where dopaminergic neurons are lost in PD. Inhibiting 15-PGDH by pharmacologic blockade or partial genetic reduction restores redox homeostasis and mitigates microglial and astrocyte activation, dopaminergic neuron loss, and motor impairment across three mouse models of PD. These models included systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), intranigral lipopolysaccharide (LPS), and intrastriatal AAV-α-synuclein with intra-ventral tegmental area α-synuclein preformed fibrils (PFFs). The neuroprotective efficacy of 15-PGDH inhibition in PD is shown to be mediated by downregulation of the dopaminergic neuronal cell death mediator lipocalin-2 (Lcn2), the pro-inflammatory cytokine interleukin-1β, the reactive oxygen generator Cybb/Nox2, and oxidative tissue damage. Mechanistically, in vitro exposure of BV2 microglia to LPS recapitulates induction of Lcn2, Cybb/N OX2 and superoxide, and all three of these effects are reversed by co-treating with prostaglandin E2 (PGE2), the prototypical degradation substrate of 15-PGDH. With a 15-PGDH inhibitor (MF-300) currently in human clinical trials for peripheral indications, these findings have translational relevance for PD.

Hydrogen sulfide (H2S) is a gaseous signaling molecule, also known as a gasotransmitter, present in nearly all mammalian organs. It plays crucial roles in regulating various physiological processes in both the brain and peripheral systems. The body maintains tight control over H2S levels, as both excessive and deficient levels can disrupt normal physiological functions and lead to disease. H2S has a significant impact on cognitive and motor functions, which are often compromised in neurodegenerative disorders. It modulates signaling and metabolism primarily by post-translationally modifying reactive cysteine residues on proteins through sulfhydration, also known as persulfidation. This chapter reviews the signaling mechanisms regulated by H2S in neurodegenerative diseases that significantly affect motor function, specifically focusing on Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), spinocerebellar ataxia (SCA), and Leigh syndrome (LS), as well as other mitochondrial disorders. While PD, HD, and SCA are linked to decreased levels of H2S, elevated levels of H2S are associated with ALS, DS, and LS. We also explore potential therapeutic applications of modulating H2S levels in the brain.

Alzheimer's disease (AD), a leading global cause of dementia, disability, and mortality, represents a critical unmet need for effective therapeutic interventions. Drug repurposing offers an expedited pathway to address this challenge compared to traditional drug development. Here, we leveraged network-based prediction and real-world patient data validation, a comprehensive strategy to identify unanticipated therapeutic applications for existing medications. Traumatic brain injury (TBI), a major risk factor for earlier and more severe AD, exhibits heterogenous clinical outcomes influenced by genetic susceptibility, suggesting that TBI-diagnosed populations represent a cohort enriched for neurodegeneration vulnerability. Building on this premise, we integrated network-based multi-omics and endophenotypic disease modules from individuals with TBI and AD histories with large real-world patient data analysis from insurance claims to prioritize repurposable drugs. A network proximity algorithm applied to TBI- and AD-associated gene sets identified statistically ranked candidates, including doxycycline and irbesartan. We then assessed all candidates' AD risk reduction potential using a nationwide Medicare database encompassing nearly 9 million individuals. In a retrospective observational study of AD-free elderly individuals monitored for up to 3 years, propensity-score adjusted survival analyses demonstrated a significantly reduced cumulative incidence of AD in doxycycline and irbesartan-prescribed individuals, with risk ratios of 0.92 and 0.83, respectively, at a 95 % confidence interval. These findings nominate doxycycline and irbesartan as potential repurposable drugs for AD and demonstrate the translational potential of synergizing network-based prediction with real-world patient evidence in drug repurposing for neurodegenerative disease if broadly applied.

Hematopoietic aging is characterized by diminished stem cell regenerative capacity and an increased risk of hematologic dysfunction. We previously identified that the prostaglandin-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH) regulates hematopoietic stem cell activity. Here, we expand on this work and demonstrate that in aged mice, (1) 15-PGDH expression and activity remain conserved in the bone marrow and spleen, suggesting it remains a viable therapeutic target in aging, (2) prolonged PGDH inhibition (PGDHi) significantly increases the frequency and number of phenotypic hematopoietic stem and progenitor cells across multiple compartments, with transcriptional changes indicative of enhanced function, (3) PGDHi-treated bone marrow enhances short-term hematopoietic recovery following transplantation, leading to improved peripheral blood output and accelerated multilineage reconstitution, and (4) PGDHi confers a competitive advantage in primary hematopoietic transplantation while mitigating age-associated myeloid bias in secondary transplants. Notably, these effects occur without perturbing steady-state blood production, suggesting that PGDHi enhances hematopoiesis under regenerative conditions while maintaining homeostasis. Our work identifies PGDHi as a translatable intervention to rejuvenate aged HSCs and mitigate hematopoietic decline. Significance Statement We identify 15-hydroxyprostaglandin dehydrogenase inhibition (PGDHi) as a strategy to enhance hematopoietic stem cell function in aging. In aged mice, PGDHi expands stem and progenitor populations, accelerates hematopoietic recovery after transplantation, and reduces myeloid bias while maintaining steady-state blood production. These findings highlight a potential therapeutic approach to restore hematopoietic resilience and improve regenerative outcomes in aging. Graphical Abstract 15-prostaglandin dehydrogenase inhibition ameliorates multiple facets of age-related hematopoietic decline. Schematic made using BioRender.com. ![Figure][1] ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes

Biliverdin reductase A (BVRA), the terminal enzyme in heme catabolism, generates the neuroprotective and lipophilic antioxidant bilirubin. Here, we identify a nonenzymatic role for BVRA in redox regulation. Through phylogenetic, genetic, biochemical, and enzymatic assays, we found that BVRA exerts critical nonenzymatic antioxidant activity. Transcriptomic analyses further revealed that BVRA physically and genetically interacts with nuclear factor erythroid-derived factor-like 2 (NRF2), a major transcriptional regulator of cellular redox signaling. ChIP-seq and RNA-seq analyses reveal that BVRA and NRF2 coordinate the expression of antioxidant genes, many of which are typically dysregulated in neurodegenerative conditions such as Alzheimer's disease. Thus, this noncanonical BVRA-NRF2 axis controls an essential pathway of redox signaling in neuroprotection. Our findings position BVRA as a dual-function integrator of antioxidant defense across both lipophilic and hydrophilic compartments, bridging these two distinct modes of redox protection in the brain.

INTRODUCTION:Glucagon-like peptide-1 (GLP-1) receptor agonists, sodium-glucose cotransporter-2 (SGLT-2) inhibitors, and dipeptidyl peptidase-4 (DPP-4) inhibitors have potential beneficial effects in Alzheimer's disease (AD). METHODS:We conducted pharmacoepidemiologic studies using two large-scale real-world databases. We fitted covariate-adjusted Cox models to compare the risks of AD among initiators of GLP-1 receptor agonists, SGLT-2 inhibitors, and DPP-4 inhibitors. RESULTS:We identified GLP-1 receptor agonist initiation compared to DPP-4 inhibitors initiation was associated with a reduced risk of AD (hazard ratio [HR] ≤ 0.69 and P value < 0.001) and SGLT-2 inhibitor initiation compared to DPP-4 inhibitor initiation was associated with a reduced risk of AD (HR ≤ 0.67 and P value < 0.001). DISCUSSION:GLP-1 receptor agonist initiation and SGLT-2 inhibitor initiation are associated with a reduced risk of AD. Randomized clinical trials are warranted to validate the causal beneficial effects of GLP-1 receptor agonists and SGLT-2 inhibitors in AD. HIGHLIGHTS:Glucagon-like peptide-1 (GLP-1) receptor agonists are significantly associated with a reduced risk of Alzheimer's disease (AD) compared to dipeptidyl peptidase-4 (DPP-4) inhibitors. Sodium-glucose cotransporter-2 (SGLT-2) inhibitors are significantly associated with a reduced risk of AD compared to dipeptidyl peptidase-4 (DPP-4) inhibitors. Two GLP-1 receptor agonists (liraglutide and semaglutide) and three SGLT-2 inhibitors (dapagliflozin, canagliflozin, and empagliflozin) are associated with a reduced risk of AD in drug-specific sensitivity analyses.

Our previous study identified that Sildenafil (a phosphodiesterase type 5 [PDE5] inhibitor) is a candidate repurposable drug for Alzheimer’s Disease (AD) using in silico network medicine approach. However, the clinically meaningful size and mechanism-of-actions of sildenafil in potential prevention and treatment of AD remind unknown. We conducted new patient data analyses using both the MarketScan® Medicare with Supplemental database (n = 7.23 million older [>65 years] subjects) and the OPTUM database (n = 11.52 million older subjects) to further test the real-world evidence of sildenafil with AD incidence. We utilized the AD patient-induced pluripotent stem cells (iPSC)-derived neuron models (5 iPSC lines from both familial and sporadic AD patients) to investigate mechanism-of-action of sildenafil’s protective effects on AD. We also treated a transgenic AD mouse model (5xFAD) with 15 mg/kg sildenafil and conducted behavioral tests, immunofluorescence staining on mouse brain sections, and single-cell RNA-seq to evaluate the sildenafil’s efficacy and brain target engagement. We found that sildenafil usage is significantly associated with reduced likelihood of AD across all four new drug cohorts (bumetanide, furosemide, spironolactone, and nifedipine). Specifically, sildenafil vs. spironolactone was associated with a 46% reduced prevalence of AD in MarketScan (HR = 54%, 95% CI 0.32-0.66, p-value = 3.33×10-5) and a 30% reduced prevalence of AD in OPTUM (HR = 70%, 95% CI 0.49-1.00, p-value = 0.05). Sildenafil treatment reduces phosphorylated tau (pTau181 and pTau231), phosphorylated GSK-3b and CDK5 in the AD patient-iPSC-derived neuron model. The 3 months sildenafil treatment significantly improved the cognition of 5xFAD transgenic mice on novel object recognition, Morris water maze and contextual fear conditioning test, supporting its therapeutic effects in AD from real-world patient data and patient iPSC model findings. RNA-seq analysis (bulk and single-cell) revealed potential biomarkers and brain target engagement to be tested in future clinical trials. Those real-world data, patient iPSC-derived mechanic, and in vivo transgenic mouse model observations suggest that sildenafil offers a potential repurposable treatment for AD. However, future clinical trials are warranted to validate the causal relationship of sildenafil in potential prevention and treatment of AD.

Alzheimer's disease (AD) presents significant challenges in drug discovery and development due to its complex and poorly understood pathology and etiology. Digital twins (DTs) are recently developed virtual real-time representations of physical entities that enable rapid assessment of the bidirectional interaction between the virtual and physical domains. With recent advances in artificial intelligence (AI) and the growing accumulation of multi-omics and clinical data, application of DTs in healthcare is gaining traction. Digital twin technology, in the form of multiscale virtual models of patients or organ systems, can track health status in real time with continuous feedback, thereby driving model updates that enhance clinical decision-making. Here, we posit an additional role for DTs in drug discovery, with particular utility for complex diseases like AD. In this review, we discuss salient challenges in AD drug development, including complex disease pathology and comorbidities, difficulty in early diagnosis, and the current high failure rate of clinical trials. We also review DTs and discuss potential applications for predicting AD progression, discovering biomarkers, identifying new drug targets and opportunities for drug repurposing, facilitating clinical trials, and advancing precision medicine. Despite significant hurdles in this area, such as integration and standardization of dynamic medical data and issues of data security and privacy, DTs represent a promising approach for revolutionizing drug discovery in AD.

BACKGROUND:While recently U.S. FDA-approved anti-amyloid beta (anti-Aβ) monoclonal antibodies (mAbs) offer new treatment approaches for patients suffering from Alzheimer's disease (AD), these medications also carry potential safety concerns and uncertainty about their efficacy for improving cognitive function. This study presents an updated meta-analysis of cognitive outcomes and side effects of anti-Aβ mAbs from phase III randomized controlled trials (RCTs) in patients with sporadic AD. METHODS AND FINDINGS:Phase III randomized, placebo-controlled blinded trials evaluating the efficacy and safety of anti-Aβ mAbs in patients with AD were identified through a search in clinicaltrials.gov, PubMed and Embase on January 14th, 2024. The retrieved studies were further screened from January 15th, 2024, to February 14th, 2024. We included studies that had been published in any language. Quality of trials was assessed using the Jadad score and publication bias was assessed using Egger's test and Funnel plot. Primary outcomes were mean changes from baseline to post-treatment in Clinical Dementia Rating scale-Sum of Boxes (CDR-SB) and AD Assessment Scale-Cognitive Subscale (ADAS-Cog) scores, and secondary outcomes were adverse events, including amyloid-related imaging abnormalities with edema (ARIA-E), and ARIA with hemorrhage (ARIA-H). Random-effects meta-analysis and meta-regression analyses were conducted. The literature search identified 13 phase III RCTs, which included 18,826 patients with mild cognitive impairment or dementia due to AD. Compared with placebo, treatment with mAbs significantly improved cognitive performance on CDR-SB (mean difference -0.25, 95% confidence interval [CI] [-0.38, -0.11]) and ADAS-Cog (standardized mean difference -0.09, 95% CI [-0.12, -0.06]), in which a negative change indicates improvement for both scores. Meta-regression analysis suggested that trials enrolling patients with early-stage AD were associated with better efficacy. Elevated risk of ARIA-E (risk ratio [RR] 9.79, 95% CI [5.32,18.01]), ARIA-H (RR 1.94, 95% CI [1.47,2.57]), and headaches (RR 1.21, 95% CI [1.10,1.32]) were noted. Statistical heterogeneity was relatively high for ARIA-E and ARIA-H, leading to wide confidence intervals and considerable variability in effect sizes, though meta-regression was conducted to address this. Furthermore, differences in trial designs introduce limitations in cross-trial comparisons. CONCLUSIONS:Anti-Aβ mAb therapy slows cognitive decline, but with small effect sizes, and raises potential concerns about ARIA and headaches.