Acid Sensing Ion Channels (ASICs) are widely expressed in the nervous system and involved in an increasing number of functions such as nociception, mechanoreception, and taste transduction, to name a few. In the CNS, ASICs are involved in synaptic plasticity, learning/memory, and in acidosis-mediated neuronal injury. In retina, ASICs are expressed in rodent, rabbit and monkey retina and pharmacological and gene knockdown studies have indicated changes in the earliest phases of electroretinogram that point to effects on phototransduction. This finding led us to investigate the electrophysiological/pharmacological properties of ASICs in cultured primate rod and cone cells. Patch-clamp recordings showed transient ASIC currents with a threshold pH of 7.0 and pH0.5 of 6.15 ± 0.03 and 6.33 ± 0.03 for cultured rod and cone cells, respectively. The currents were almost completely blocked by amiloride and highly sensitive to PcTx-1. Our results for the first time demonstrate the expression of functional ASICs on primate photoreceptors and suggest that ASIC currents in these cells are mediated predominantly by homomeric ASIC1a channels.
Strenuous exercise induces microstructural muscle damage, leading to delayed onset muscle soreness and reduced performance. Although structural changes are well documented, subsequent inflammatory responses are not fully understood. Research has mainly examined leukocyte infiltration and cytokine expression, while low-abundance bioactive lipid mediators remain understudied. Nutritional strategies, such as palmitoylethanolamide (PEA) supplementation, can modulate these mediators and promote anti-inflammatory, pro-resolving conditions, which may improve recovery. Therefore, the present study evaluated the effect of PEA on the abundance of bioactive lipid mediators in skeletal muscle tissue of healthy males following muscle damaging exercise (MDE). 10 participants were included in a double-blind crossover study where they received PEA (2 × 350 mg/d, Levagen+) or placebo (PLA, maltodextrin), in a randomized order. In each experimental condition participants performed an MDE bout (24 × 10 eccentric contractions of the knee extensors on an isokinetic dynamometer). Muscle biopsies were collected at baseline and 48 h following MDE and analysed for lipid mediator profile via LC-MS/MS–based lipidomics. Many lipid mediators decreased 48 h post-exercise in PLA, whereas they remained unchanged or increased in PEA. This pattern was observed for mediators derived from AA (12-HHTrE, 11-HETE, 12-HETE, 15-HETE, 15-epi-LXA4, 14,15-EpETrE, 5,6-DiHETrE), DHA (4-HDoHE), LA (9-HODE, 13-HODE) and ALA (9-HOTrE, 13-HOTrE). MCTR3 levels were consistently higher in PEA compared to PLA, whereas concentrations of LXB4 and AT-RvD3 were consistently lower in PEA compared to PLA, independent of exercise. In conclusion, PEA supplementation attenuated or counteracted the decline in lipid mediators following exercise, indicating that PEA partially enhances bioactive lipid tone in response to strenuous exercise.
Pharmacological inhibition of the chloride-bicarbonate exchanger pendrin with PDSinh-C01 potentiates the diuretic action of furosemide in healthy mice. Because pendrin contributes to acid-base regulation and blood pressure control, it may represent an attractive therapeutic target in chronic kidney disease (CKD). We investigated whether this pendrin inhibitor improves metabolic acidosis and salt-sensitive hypertension in the 5/6 nephrectomy (5/6Nx) model of CKD. Seven-week-old female Sprague Dawley rats underwent 5/6Nx and implantation of telemetry devices for blood pressure monitoring. All animals received a high-salt (2
Linking the distinctive structural and functional properties of lipids belonging to different signaling classes is a frontier of physiology. The present minireview focuses on the endocannabinoidome phospholipase NAPE-PLD, which has bile acids (BAs) as structural cofactors at membrane interface and generates bioactive N-acylethanolamines (NAEs) that promote pleiotropic effects. NAPE-PLD is thus at the crossroads of both their physiological functions, an area of ongoing research. The wide internal channel of NAPE-PLD facilitates the transmembrane transport of pyridoxal 5'-phosphate (PLP) and can support the activity of PLP-dependent enzymes in mitochondria, peroxisome and other subcellular compartments. Recent insights demonstrate that drugs and agents that stabilize NAPE-PLD can control blood pressure, vascular resistance and cardiovascular morbidity in clinics, offering new perspectives on the interaction between NAEs and BAs in cardiometabolic and neurological disorders.
Regular physical activity elicits coordinated molecular adaptations across skeletal muscle, the cardiovascular system, metabolic organs and the brain, underpinning improvements in performance and cardiometabolic health. While classical signaling pathways such as AMPK–PGC‑1α, Ca²⁺/calcineurin, and mTORC1 have been extensively characterized, long non-coding RNAs (lncRNAs) have recently emerged as key regulators of exercise-induced remodeling. Here, we synthesize current evidence on lncRNAs as molecular mediators of exercise adaptations, drawing on mechanistic studies and systems-level transcriptomics. In skeletal muscle, the exercise-induced lncRNAs CYTOR and TUG1 modulate fast-twitch myogenesis, mitochondrial function and fiber-type specification. In the heart, CPhar, lncExACT1 and Mhrt779 discriminate physiological from pathological hypertrophy and encode antihypertrophic “memory,” whereas endothelial NEAT1 integrates aerobic training with m⁶A-modulated pyroptosis and atheroprotection. MALAT1 mediates neuroprotection after exercise preconditioning in ischemia/reperfusion models. Omics and network analyses reveal highly modality-, tissue- and cell-type–specific lncRNA programs during human training and across multiple organs. Emerging clinical data support circulating lncRNAs such as MALAT1 and HOTTIP as candidate biomarkers of vascular function and training adaptation. Collectively, lncRNAs constitute a hidden regulatory layer that shapes the quality, magnitude and persistence of exercise-induced adaptations. However, mechanistic evidence is currently limited to a small number of “flagships” lncRNAs, and non-muscle tissues and inter-organ communication remain underexplored. Priorities include functional validation of atlas-derived candidates, dissection of exerkine lncRNAs, and integration of lncRNA biology into precision exercise medicine.
Acid-sensing ion channels (ASICs) are widely recognized as proton (H+)-gated cation channels that respond to extracellular acidification associated with pathological states such as ischemia, inflammation, and epilepsy. However, an emerging body of evidence compels a broader conceptual reframing: ASICs function as dynamic sensors of metabolic state, integrating real-time signals of neural activity, including CO₂-derived H+, lactate, and nano-domain pH transients, to regulate neuronal excitability and intercellular communication. Here, we review the mechanisms by which activity-dependent pH shifts arise in the brain, how lactate potentiates ASIC gating through divalent-cation chelation and direct channel modulation, and how the tripartite neuron-astrocyte-vascular unit functions as a spatially organized pH-sensing system. We discuss how astrocytes simultaneously buffer extracellular pH and express ASICs, placing them at the center of a bidirectional metabolic feedback loop, and how ASICs in cerebrovascular cells may link neural metabolic load to vascular tone. Finally, we identify key open questions, including the spatial scale of physiologically relevant pH nano-domains, the role of ASIC tachyphylaxis as a “use-history” sensor, and whether ASIC-dependent metabolic signaling shapes circuit-level dynamics during sleep-wake transitions and high-demand cognitive states. This perspective reframes ASICs not merely as damage sensors but as constitutive physiological transducers of brain metabolic activity.
Mucociliary transport (MCT) is the dominant mechanical host defense system in human airways. Although the importance of the peripheral airway in the pathophysiology of bronchial asthma has recently attracted attention, the characteristics of MCT in the peripheral airway during asthma remain unclear. This study aimed to investigate MCT velocity in the central and peripheral airways and the effects of thymic stromal lymphopoietin (TSLP) on MCT. Central and peripheral airways were isolated from freshly obtained porcine airways immediately after slaughter. The airway specimens were mounted in a custom-built fluorescence microscopy–based measurement system. MCT velocity and ciliary beat frequency (CBF) were measured under the following conditions: without stimulation, in the presence of a low concentration of acetylcholine (ACh), and after stimulation TSLP, which reflects the pathophysiological condition of bronchial asthma. MCT velocity in the peripheral airways was slower than that in the central airways at less than one tenth (median: 75.40 μm/sec vs. 2.63 μm/sec). Under physiologically low ACh concentrations, MCT velocity was increased in the peripheral airway but not in the central airway. TSLP addition partially inhibited MCT velocity in both the central and peripheral airways by approximately two-thirds to one-half. TSLP also partially inhibited the CBF in both the central and peripheral airways from approximately two-thirds to one-third. Furthermore, TSLP receptor (TSLPR) expression was confirmed in airway tissues by immunohistochemical staining. The inhibitory effects of TSLP on MCT velocity were completely abolished by pre-incubation with a Janus kinase (JAK) inhibitor. In conclusion, TSLP has the potential to reduce MCT velocity, especially in the peripheral airways, by inhibiting TSLPR signaling pathways, resulting in impaired CBF. The characteristics of MCT differ between the central and peripheral airways. Importantly, TSLP-induced MCT impairment may aggravate mucus plug formation in the peripheral airways in patients with bronchial asthma.
Functional assessment is essential to quantify kidney graft quality early after kidney transplantation. Kidney transplantation is inherently associated with ischemia–reperfusion-injury, a noxious insult for proximal tubule cells that may not be captured by glomerular function markers. The urine ammonium-pH index (uAPI) is a functional measure of the tubulointerstitial capacity for ammonium excretion. Here, we aimed to investigate the association between the uAPI and graft function in kidney transplant recipients. In this post-hoc observational analysis of the CONTEXT trial (NCT01395719), kidney transplant recipients with available urine samples were divided into an exploration cohort (n = 112) and a validation cohort (n = 88). The uAPI was assessed at baseline, 90 min after reperfusion, day 1, 2 and 3 posttransplant. Day 6 kidney graft biopsies were stained for VCAM1 as a marker of tubular injury. Outcomes were delayed graft function, estimated time to 50
The kidney slit diaphragm (SD) connects the foot processes of glomerular podocytes, anatomically forming the outermost part of the three-layered glomerular filtration barrier. The SD is a large molecular polymer that, together with the foot processes, covers the glomerular capillaries and has diverse functions. It establishes a strong yet flexible cell-cell contact between foot processes from neighboring podocytes and additionally acts as a dynamic signaling platform linking structural integrity with cellular responses. Understanding the physiology of the SD has been hampered by limited structural insights and a lack of precise knowledge of protein composition of its building blocks. The recent convergence of the proteomic analyses of the SD with atomically resolved structures and in situ cryo-electron tomography imaging have led to the fishnet SD. The fishnet SD is based on the high-resolution 3D cryo-electron tomographic images of native glomeruli that revealed an unexpected fishnet architecture, observed in mouse, fly and human. This breakthrough has provided a new and markedly different view of how we understand and analyze the SD. It provides important principles for understanding spatial self-organization, assembly, turnover, and force compensation and offers an important basis for functional investigations, including the elucidation of molecular mechanisms of clinically relevant diseases.
α-Klotho (hereafter Klotho) was discovered as an aging-suppressor protein whose function is intrinsically dependent on the kidney. Its shed ectodomain, soluble Klotho (sKlotho), is detectable in blood and urine. As an obligate co-receptor for endocrine fibroblast growth factor 23, Klotho operates at the intersection of mineral metabolism and chronic kidney disease (CKD). Within the kidney, Klotho expression is moderate in the proximal tubule but strongly enriched in the distal nephron, although the functional significance of this heterogeneity remains unclear. Recent findings from nephron segment-specific Klotho knockout mice reveal functional specialization of tubular Klotho along the nephron. According to the revised model, distal nephron Klotho regulates calcium reabsorption, bone remodeling, and urinary sKlotho levels. By contrast, proximal tubular Klotho regulates phosphate and vitamin D metabolism and is likely the principal source of circulating sKlotho; its loss recapitulates hyperphosphatemia, FGF23 resistance, and ageing-like phenotypes. This review re-evaluates the long-standing paradigm of renal Klotho biology in light of emerging evidence for functionally distinct proximal and distal nephron Klotho. Together, these insights place the kidney and its tubular Klotho heterogeneity at the center of mineral metabolism, aging and CKD.
Neuropeptide S (NPS) signaling is critically involved in arousal, sleep–wake regulation, fear and anxiety, and related forms of learning and memory, yet comparatively little is known about whether intrinsic properties of identified NPS neurons differ between sexes or fluctuate across the female estrous cycle. Here, we performed whole-cell patch-clamp recordings from genetically identified NPS-eGFP neurons in acute horizontal brainstem slices containing the peri–locus coeruleus (periLC) region. We show that periLC NPS neurons can be subdivided into two electrophysiologically distinct classes based on their discharge patterns from hyperpolarized membrane potentials: a delayed-onset firing phenotype (type I) and a regular-spiking phenotype (type II). Pharmacological and voltage-clamp analyses indicate that differential contribution of a transient A-type potassium current (IA), consistent with Kv4 channel function, is a key determinant of these firing phenotypes and provides a mechanism for gain control in type I neurons. Across male and female mice, we did not detect robust sex differences in the relative abundance of these neuronal classes or in overall excitability measures, suggesting that baseline intrinsic properties of periLC NPS neurons are broadly comparable between sexes. In contrast, estrous staging revealed a selective modulation of intrinsic discharge in females: during non-receptive stages (metestrus/diestrus), type I neurons exhibited higher spike output and increased instantaneous firing frequencies compared with receptive stages (proestrus/estrus), whereas type II neurons were comparatively stable across the cycle. These findings provide a cellular mechanism by which ovarian state may tune NPS neuron output and, consequently, the impact of NPS signaling on downstream circuits controlling arousal and stress-related behaviors.
Diabetic nephropathy (DN) is characterized by a decline in renal function resulting from hyperglycaemia and is often requiring dialysis or renal transplantation. Yet, the signalling events causing DN and the effective treatment options are poorly understood. Changes in the signalling of cyclic nucleotides and their regulated kinases are hypothesized to be involved in its development. Protein kinase A (PKA) signalling pathways are known to modulate extracellular matrix metabolism and exert antifibrotic effects. Multiple isoforms of PKA regulatory and catalytic subunits exist, leading to functional specificities of the kinase arising from different combinations of these isoforms. However, localization of the specific PKA subunits, as well as other signalling proteins involved in this pathway, still need to be explored comprehensively. To gain an overview about PKA distribution, kidneys were analysed by immunohistochemistry and stained for different PKA subunits. Type 1 diabetes was induced by streptozotocin in wildtype (WT) and endothelial NOS knockout (eNOS-KO) mice. The catalytic subunit expression was quantified and compared between healthy and diabetic kidneys. Analysis of expression patterns of the PKA catalytic subunits Cα and Cβ reveal differences across segments of the kidney and in intracellular localization. Cα exhibited ubiquitous expression in all renal cell types. In contrast, Cβ only shows a high expression in proximal tubules, while its expression in other segments is comparatively weak. No significant changes in Cα or Cβ expression are detectable in diabetic mice or eNOS-KO mice compared to WT mice.
Cellular adaptation to hypoxia is essential for maintaining function and survival. While most hypoxic responss are mediated by hypoxia‑inducible factor signaling, the oxygen‑dependent ADO–RGS (2‑Aminoethanethiol-Dioxygenase—Regulator of G‑Protein Signaling) pathway has recently been implicated in oxygen‑sensitive regulation of G‑protein signaling. The kidneys are particularly vulnerable to hypoxia, a major contributor to chronic kidney disease. Because a systematic characterization of ADO and its RGS substrates across renal cell types is lacking, this study examined their spatial expression patterns in mouse and human kidneys under (patho)physiological conditions. Ado and Rgs4, Rgs5, and Rgs16 expression was mapped in mouse kidney sections under normoxic, hypoxic, and fibrotic conditions using RNAscope™, complemented by RT‑qPCR. Mouse data were compared with ADO-RGS expression patterns in human biopsies. Ado expression was uniform across renal regions, cell types, and conditions. Besides its baseline presence in vascular cells, Rgs4 showed strong induction in cortical and outer medullary fibroblasts during anemia. It was also upregulated in fibroblasts and proximal tubules within fibrotic lesions. Rgs5 was highly expressed in vascular structures and demonstrated hypoxia‑induced upregulation in medullary fibroblasts and vasa recta, with moderate induction under fibrotic conditions. Tubular epithelial expression also occurred during fibrosis. Rgs16 was mostly expressed in Pdgfrb⁺ interstitial cells in fibrotic kidneys. Human kidney-disease biopsies also displayed distinct RGS4 and RGS5 expression patterns. Overall, these findings suggest that while ADO is consistently present, the functional impact of ADO–RGS signaling may be driven by dynamic, cell‑type‑specific regulation of RGS genes during acute and chronic hypoxic stress.
Skeletal muscle function is critically dependent on the metabolism of cholesterol and its sarcolemmal levels. Decreased cholesterol availability is associated with various pathological conditions, causing muscle weakness. Here, we tested the hypothesis that a reduction in cholesterol content can affect the resting membrane potential, an essential parameter for membrane transport and electro-mechanical coupling in fibers of mouse diaphragm, the main respiratory muscle. 20-min exposure to methyl-β-cyclodextrin (MβCD) concentration-dependently reduced the level of muscle cholesterol. This effect was more pronounced in surface muscle fibers, where MβCD at a concentration of 30 mM decreased cholesterol content by 40
The sodium-hydrogen exchanger isoform 3 (NHE3) is a critical mediator of proximal tubule and thick ascending limb Na+ reabsorption and H+/NH4+ secretion, yet the physiological implications of its upregulation during low K+ intake remain poorly understood. We hypothesized that renal NHE3 is important for the acid-base response during K+ depletion. To test this, we utilized kidney-specific NHE3 knockout (NHE3KS−KO) mice. Following 10 days of a K+-deficient diet (< 30 ppm), NHE3KS−KO mice exhibited exacerbated hypokalemia compared to control mice, despite near complete elimination of urinary K+ excretion and comparable levels of ROMK and BKα protein abundance in both genotypes. Control and NHE3KS−KO mice developed hypernatremia secondary to a urinary concentrating defect; however, this was associated with a 2-fold greater fluid intake in NHE3KS−KO mice. These effects occurred without changes in glomerular filtration rate. Both genotypes developed metabolic acidosis, which was significantly more severe in NHE3KS−KO mice. This exacerbated acidosis correlated with a 60
Putative gastroprotective effects of xenin-25 were investigated in an indomethacin-induced acute ulcer model. Male Sprague-Dawley rats were randomly assigned to control, saline-treated ulcer, xenin-25-treated ulcer groups. Gastric ulcer was induced with indomethacin (25 mg/kg, subcutaneously) and xenin-25 (0.2, 2, 20 µg/kg) or saline was given subcutaneously immediately after and at 2 h following indomethacin injection. In order to investigate whether the effects of xenin-25 depend on vagal afferent fibres, two additional groups underwent vagal afferent denervation (VAD) by bilateral perivagal capsaicin application (1
Aldehyde dehydrogenase 2 (ALDH2) is a mitochondrial enzyme that metabolizes 4-hydroxynonenal (4-HNE), a lipoperoxidation-derived aldehyde that promotes oxidative stress. ALDH2 is therefore considered part of the antioxidant defense. On the other hand, the hormone aldosterone enhances the production of reactive oxygen species (ROS) in many cell types. During skeletal muscle development (myogenesis), myoblasts fuse to form multinucleated cells, called myotubes. In the present study, we investigated the potential of ALDH2 to regulate ROS production in C2C12 cells and its effects on myotube formation during early (0–3 days) and late (4–9 days) stages. Western blot results indicate that these cells actually express ALDH2. Interestingly, incubating cells (1.5–24h) with the pro-oxidant compounds H2O2, 4-HNE, aldosterone, and daidzin (ALDH2 antagonist) enhanced ROS production. In contrast, two ALDH2 agonists (Alda-1 and AD-5591) prevented, with similar potency, the 4-HNE– and aldosterone–induced oxidative stress. We next demonstrated that incubating cells with H2O2 (0.5–5 µM) induces a biphasic regulation of myotube formation, with early inhibition and late stimulation. This H2O2-induced biphasic regulation was also reproduced by aldosterone, daidzin, and another ALDH2 antagonist (CVT-10216). Consistent with their effects on oxidative stress, the ALDH2 agonists Alda-1 and AD-5591 eliminated the regulation of myoblast fusion by H2O2 and aldosterone. Additional data suggest that aldosterone acts through the mineralocorticoid receptor, and both calpain and p38-MAPK are also implicated. These findings indicate that ALDH2 is essential for regulating oxidative stress in myogenic cells and is involved in a signaling pathway that governs myoblast fusion through biphasic and opposing mechanisms.
Experimental medicine studies, small, mechanistically focused investigations, have historically driven key discoveries in human physiology and pharmacology. Despite their foundational role, these studies are increasingly marginalised in today’s drug development environment due to economic pressures, regulatory conservatism, and an overemphasis on statistical endpoints from large-scale trials. This article traces the historical roots and enduring value of experimental medicine, distinguishes it from current early phase drug development studies, and explores the structural forces behind its decline. N-of-1 trials are discussed as a systematic extension of these principles, offering precision insights at the individual level. We apply this discussion to chronic kidney disease (CKD), a field where slow progression and heterogeneous pathophysiology make early mechanistic studies especially valuable. We argue that bypassing such studies in favour of speed represents a strategic gamble that may misdirect costly late-phase trials. Integrating mechanistic insights with statistical power is not superfluous, but essential, particularly in complex diseases like CKD where understanding why and how interventions work may matter as much as whether they do. We acknowledge that achieving this vision necessitates overcoming significant structural, economic, and cultural barriers within the current drug development environment; however, the costs of inaction, manifest as trial failures, patient harm, and missed therapeutic opportunities, are potentially much greater.
Obesity is a major driver of type 2 diabetes, underscoring the urgent need for therapies that target both energy expenditure and glucose homeostasis. Parathyroid hormone (PTH) has been implicated in promoting adipose tissue browning and thermogenesis, but its metabolic impact in the context of obesity remains uncertain. We aimed to examine the effects of PTH in ob/ob mice, a leptin-deficient model of obesity and diabetes. A single dose or daily injections of human PTH(1–34) were administered to ob/ob mice and their wild-type littermates. Metabolic outcomes, adipose tissue thermogenesis, and appetite-regulating pathways were assessed. A pair-feeding study was also performed to isolate the effect of PTH from food intake. A single acute dose of PTH upregulated thermogenic gene expression in adipose tissue in a dose-dependent manner. However, repeated daily PTH administration failed to sustain adipose browning or improve insulin resistance and hyperglycemia; instead, it exacerbated weight gain, primarily due to increased food intake. Mechanistically, PTH enhanced gastric ghrelin production and upregulated hypothalamic AgRP expression, suggesting a central orexigenic effect. In pair-feeding experiments, PTH-treated mice showed no significant improvements in adiposity or metabolic parameters, even when caloric intake was matched. Although PTH transiently promotes thermogenesis in adipose tissue in ob/ob mice, sustained exposure exacerbates hyperphagia without meaningful metabolic benefit. These findings highlight the challenges of targeting PTH signaling for treating obesity-related diabetes.
Sex differences in vascular adrenergic responsiveness contribute to differential regulation of vascular tone. Female vessels exhibit enhanced β-adrenergic relaxation compared with males, but the role of oestrogen receptors in maintaining this phenotype and the capacity of sex hormone exposure to reprogram vascular β-adrenoceptor expression remain incompletely understood. Thoracic aorta and mesenteric arteries from Wistar Kyoto rats were examined following pharmacological oestrogen receptor inhibition or cross-sex hormone treatment. Vascular reactivity was assessed using wire myography, and β₁-, β₂-, and β₃-adrenoceptor mRNA expression was quantified by qPCR. Oestrogen receptor blockade with fulvestrant enhanced norepinephrine-induced vasoconstriction and reduced β-adrenergic relaxation in both conduit and resistance arteries. These functional alterations were accompanied by an approximately 50
