American journal of physiology. Cell physiology最新文献

Very-low-carbohydrate diets (LCHF; <50 g/day) have been debated for their potential to lower pre-exercise muscle and liver glycogen stores and metabolic efficiency, risking premature fatigue. It is also hypothesized that carbohydrate ingestion during prolonged exercise delays fatigue by increasing carbohydrate oxidation, thereby sparing muscle glycogen. Leveraging a randomized crossover design, we evaluated performance during strenuous time-to-exhaustion (70% V̇o_2max) tests in trained triathletes following 6-wk high-carbohydrate (HCLF, 380 g/day) or very-low-carbohydrate (LCHF, 40 g/day) diets to determine 1) if adoption of the LCHF diet impairs time-to-exhaustion performance, 2) whether carbohydrate ingestion (10 g/h) 6-12× lower than current CHO fueling recommendations during low glycogen availability (>15-h pre-exercise overnight fast and/or LCHF diet) improves time to exhaustion by preventing exercise-induced hypoglycemia (EIH; <3.9 mmol/L; <70 mg/dL), and 3) the "keto-adaptation" time course through continuous substrate monitoring while caloric intake, physical activity, and fat-free mass are maintained. Time-to-exhaustion performance was similar across both dietary interventions. Minimal carbohydrate supplementation prevented EIH and significantly increased time to exhaustion equivalently in LCHF and HCLF interventions (22%). The LCHF diet significantly lowered 24-h glucose concentrations, which normalized after 4 wk, at the same timepoint peak blood ketone (R-β-hydroxybutyrate) concentrations normalized. These findings 1) demonstrate that an LCHF diet sustains strenuous endurance performance, 2) establish that minimal carbohydrate supplementation was sufficient to enhance exercise performance on LCHF and HCLF diets by mitigating EIH, and 3) indicate that a minimum 4-wk adaptation period to an LCHF diet is required to ensure normalization of metabolic homeostasis, glycemic control, and exercise performance.NEW & NOTEWORTHY This study examines the belief that very-low-carbohydrate diets (LCHF) impair prolonged exercise performance during strenuous exercise by comparing it with high-carbohydrate diets in competitive triathletes. After 6-wk diet adaptation, time-to-exhaustion (TTE) performance was similar across both diets. Minimal carbohydrate supplementation (10 g/h) during exercise eliminated exercise-induced hypoglycemia and improved TTE by 22% on both diets. These findings suggest that LCHF diets do not impair exercise performance and require a 4-wk adaptation period for metabolic homeostasis.

Over the past few decades, the primary cilium, an inconspicuous cell organelle, has increasingly become the focus of current research. The primary cilium is a microtubule-based, nonmotile, antenna-like structure that is present in almost all mammalian cells. The ciliary membrane incorporates a large number of receptor molecules, which further characterize this cellular organelle. These include receptors of the Sonic hedgehog (Shh)-, Wnt-, or platelet-derived growth factor (PDGF) signaling pathways. For this reason, as well as due to the fact that extracellular signaling molecules can bind to the ciliary membrane, primary cilia have been named "the antenna of the cell." In addition to their signaling function, the association of ciliary dysfunctions with a variety of diseases, so-called ciliopathies, underscores the importance of this functional cellular structure. Recent studies have also implicated primary cilia in the adaptation to low-oxygen conditions, which are characteristic of ischemia, such as in stroke or myocardial infarction, or tumor entities. The aim of this review is to provide an overview of these multiple facets and to take a closer look at the evolution of an inconspicuous cell organelle to a major player in hypoxia.

Long noncoding RNA (lncRNA) and N6-methyladenosine (m6A) methylation modification have recently been suggested as potential functional modulators in ovarian endometriosis, however, the function and mechanism of m6A-modified lncRNA in ovarian endometriosis remain poorly understood. In this study, we demonstrated that lncRNA UBOX5-AS1 expression was significantly elevated in ovarian endometriosis tissue and primary ectopic endometrial stromal cells. The expression of lncRNA UBOX5-AS1, which has m6A modifications, was highly positively correlated with demethylase Alk B homologous protein 5 (ALKBH5) expression and autophagy. Functional studies revealed that increased ALKBH5 and lncRNA UBOX5-AS1 expression promoted cell autophagy, proliferation, and invasion in endometriosis in vitro. LncRNA UBOX5-AS1 mediates ALKBH5-regulated autophagy, proliferation, and invasion. ALKBH5-mediated autophagy facilitates cell proliferation, migration, and invasion. In vivo, the knockdown of ALKBH5 inhibited endometriotic lesion growth. Mechanistically, we observed that ALKBH5 mediated the m6A demethylation of lncRNA UBOX5-AS1 and promoted its expression. Thus, our findings highlight that ALKBH5/lncRNA UBOX5-AS1 might serve as potential targets for ovarian endometriosis therapy in the future.NEW & NOTEWORTHY In the present study, we investigated the role and potential molecular mechanism of long noncoding RNA (lncRNA) UBOX5-AS1 in ovarian endometriosis progression. Combined with the aforementioned, we proposed the hypothesis that lncRNA UBOX5-AS1 regulated by Alk B homologous protein 5 (ALKBH5)-mediated N6-methyladenosine (m6A) modification contributes to the progression of ovarian endometriosis progression.

The optimum length for force generation (L₀) increases as activation is reduced, challenging classic theories of muscle contraction. Although the activation dependence of L₀ is seemingly consistent with length-dependent Ca²⁺ sensitivity, this mechanism cannot explain the apparent force dependence of L₀ or the effect of series compliance on activation-related shifts in L₀. We have tested a theory proposing that the activation dependence of L₀ relates to force depression resulting from shortening against series elasticity. This theory predicts that significant series compliance would cause tetanic L₀ to be shorter than the length corresponding to optimal filament overlap, thereby increasing the activation dependence of L₀. We tested this prediction by determining L₀ and maximum tetanic force (P₀) with (L_{0_spring}, P_{0_spring}) and without added compliance in bullfrog semitendinosus muscles. The activation dependence of L₀ was characterized with the addition of twitch and doublet contractions. Springs attached to muscles gave added fixed-end compliances of 11%-39% and induced force depression for tetanic fixed-end contractions (P_{0_spring} < P₀). We found strong, negative correlations between spring compliance and both P_{0_spring} (r² = 0.89-0.91) and L_{0_spring} (r² = 0.60-0.63; P < 0.001), whereas the activation dependence of L₀ was positively correlated to added compliance (r² = 0.45, P = 0.011). However, since the compliance-mediated reduction in L₀ was modest relative to the activation-related shift reported for the bullfrog plantaris muscle, additional factors must be considered. Our demonstration of force depression under novel conditions adds support to the involvement of a stress-induced inhibition of cross-bridge binding.NEW & NOTEWORTHY Length-dependent Ca²⁺ sensitivity does not fully explain the activation dependence of optimum length (L₀). We demonstrate using an isolated muscle preparation and added series compliance that substantial force depression can arise during an isometric contraction, causing tetanic L₀ to shift to a shorter length. Our findings illustrate that series compliance, via the work and length dependencies of force depression, partially uncouples force generation from myofilament overlap, which ultimately increases the activation (or force) dependence of L₀.

Evidence suggests that the progression of acute kidney injury (AKI) is driven by tubular epithelial cell (TEC) injury. However, the role of ferroptosis during the regulatory process remains unclear. Fifty-three patients with AKI were included to examine the expressions of Rab7, glutathione peroxidase 4 (GPX4), and Hif-1α by immunohistochemistry. The relationship between these expressions and serum creatinine (Scr) and blood urea nitrogen (BUN) levels was analyzed. After inducing AKI and ferroptosis through bilateral renal artery ischemia-reperfusion injury (I/R) in vivo and hypoxia in vitro, we examined the expression of Rab7. The injury and ferroptosis were observed following the administration of erastin or ferrostatin-1 (Fer-1), as well as the downregulation of Rab7. In addition, we investigated the degradation of GPX4 and chaperone-mediated autophagy (CMA). Finally, we assessed the injury and ferroptosis after the combination of RAS-selective lethal 3 (RSL3) and downregulation of Rab7. GPX4 exhibited an inverse correlation with Hif-1α, Scr, BUN, and Rab7. Conversely, Rab7 was positively correlated with Scr and BUN. Both in vivo and in vitro models resulted in elevated levels of ferroptosis and Rab7. Erastin exacerbated ferroptosis and injury, but this effect was mitigated by Fer-1. Downregulation of Rab7 reversed the increased ferroptosis and injury. Hypoxia enhanced lysosomal transport and degradation of GPX4 through activation of CMA. Furthermore, the reversal of these effects was observed upon the downregulation of Rab7. However, the results obtained from Rab7 downregulation were subsequently reversed by RSL3. Ferroptosis is important in TEC injury during AKI and Rab7 promotes tubular ferroptosis by facilitating CMA-mediated degradation of GPX4.NEW & NOTEWORTHY To explore the mechanism underlying ferroptosis in I/R-induced renal injury and to confirm the effect of Rab7, we first evaluated ferroptosis in renal biopsy samples, and then examined Rab7 expression and renal tubular injury during AKI in vivo and in vitro. Finally, we performed in vitro experiments to investigate the specific role of Rab7 in the regulation of ferroptosis and showed that the regulatory mechanism was related to CMA-mediated GPX4 degradation in renal TECs.

Most patients with lung cancer experience cancer cachexia (CC), a syndrome of skeletal muscle and adipose tissue wasting. Knowledge of body composition changes in patients is limited, however, because most studies have been cross-sectional, comparing patients with non-cancer controls or patients with and without CC. Few studies, in contrast, have evaluated body composition in patients with lung cancer over time. This review examines our current understanding of longitudinal body composition changes in patients with lung cancer and identifies modifying factors contributing to variation in muscle and adipose tissue wasting, focusing on biological sex. We identified 32 studies conducting longitudinal measurements of body composition by computed tomography, bioelectrical impedance, dual x-ray absorptiometry or total body nitrogen, with a total of n=3,951 patients (35% female). All studies evaluated changes following diagnosis while patients were receiving treatment. Most studies reporting muscle-specific outcomes show decreased skeletal muscle mass, with more pronounced muscle wasting in males and male-enriched populations. In a small number of studies reporting muscle density, the majority show increased myosteatosis. Adiposity changes are less frequently reported, although wasting appears more prevalent in late-stage disease. Further studies are needed to define adipose changes along the lung cancer continuum. Our review emphasizes the need for balanced recruitment based on biological sex and sex-based analyses. Additionally, consensus reporting of relevant patient data and outcomes in future studies will allow for meta-analysis and assist in the development of effective treatments for lung CC.

O-GlcNAcylation is a post-translational modification characterized by the covalent attachment of a single moiety of GlcNAc on serine/threonine residues in proteins. Tyrosine hydroxylase (TH), the rate-limiting step enzyme in the catecholamine synthesis pathway and responsible for production of the dopamine precursor, L-DOPA, has its activity regulated by phosphorylation. Here, we show an inverse feedback mechanism between O-GlcNAcylation and phosphorylation of TH at serine 40 (TH pSer40). First, we showed that, during PC12 cells neuritogenesis, TH O-GlcNAcylation decreases concurrently with the increase of pSer40. In addition, an increase in O-GlcNAcylation induces a decrease in TH pSer40 only in undifferentiated PC12 cells, while the decrease in O-GlcNAcylation leads to an increase in TH pSer40 levels in both undifferentiated and differentiated PC12 cells. We further show that this feedback culminates on the regulation of L-DOPA intracellular levels. Interestingly, it is noteworthy that decreasing O-GlcNAcylation is much more effective on TH pSer40 regulation than increasing its levels. Finally, ex vivo analysis confirmed the upregulation of TH pSer40 when O-GlcNAcylation levels are reduced in dopaminergic neurons from C57Bl/6 mice. Taken together, these findings demonstrate a dynamic control of L-DOPA production by a molecular crosstalk between O-GlcNAcylation and phosphorylation at Ser40 in tyrosine hydroxylase.

During acute myocardial infarction, the composition of the extracellular matrix changes remarkably. One of the most notable changes in the extracellular matrix is in the accumulation of collagen; however, hyaluronan rivals collagen in its abundance. Yet, the extent to which specific cells and enzymes may contribute to such accumulation has been largely unexplored. Here, we hypothesized that activated cardiac fibroblasts produce hyaluronan via hyaluronan synthase 2 (HAS2). We show that hyaluronan accumulates following myocardial infarction and persists through at least four weeks. Our analyses of failing heart RNA sequencing data suggest fibroblasts are the cells most changed in the expression of HAS2. Given these insights, we used HAS2 gain- and loss-of-function approaches to examine the extent to which activated cardiac fibroblasts produce hyaluronan. TGFβ-induced activation of fibroblasts caused a significant increase in Has2 mRNA and concomitant accumulation of hyaluronan greater than 1 MDa in size. Deletion of Has2 abrogated TGFβ-induced production of hyaluronan. In addition, overexpression of Has2 was sufficient to cause an increase in hyaluronan accumulation in the absence of TGFβ-induced activation. Our data indicated negligible impacts of Has2 on proliferation, migration, and collagen production. Exposing fibroblasts to exogenous hyaluronan also had minimal impact on fibroblasts. We also assessed whether fibroblast-borne Hyal2 plays a role in the degradation of hyaluronan, and our data indicated little impact of Hyal2 on hyaluronan accumulation (or even any impacts on the transcriptional profile of fibroblasts). Activated fibroblasts produce high molecular weight hyaluronan via Has2, which occurs independent of other fibroblast functions.

The activation of hepatic stellate cells (HSCs) from a quiescent state is a cause of liver fibrosis and a therapeutic target. HSCs are resident mesenchymal cells located in the space of Disse, exhibiting specialized morphological characteristics such as a stellate shape, large lipid droplets, and direct adhesions to hepatocytes via microprojections called HSC spines. Morphological alterations in HSCs play a crucial role in initiating their activation. However, the mechanisms regulating these changes remain unexplored. In this study, we analyzed the morphological alterations associated with HSC activation in vivo using carbon tetrachloride treatment and identified the key factors regulating these changes in vitro. Following carbon tetrachloride treatment, HSCs exhibited shortened cell processes and HSC spines, adopting an oval shape. Subsequently, the HSCs underwent further morphological changes into two activated forms: flattened and complex shapes. In vitro, activation of cell division cycle 42 (Cdc42) maintained the morphological characteristics of quiescent HSCs. Cdc42 activation in HSC cell lines inhibited the expression of markers associated with activated HSCs. Cdc42 inhibitor treatment in vivo prevented quiescent HSCs from maintaining their morphological characteristics and hindered activated HSCs from reverting to the quiescent state. Additionally, HSCs around fibrotic areas in the human liver exhibited morphological alterations indicative of early activation. These findings demonstrate that Cdc42 is a crucial regulator of morphological and molecular alterations associated with HSC activation, identifying it as a novel target for the development of therapeutic agents against liver fibrosis.

Hepatic lipotoxicity, resulting from excessive lipid accumulation in hepatocytes, plays a central role in the pathogenesis of various metabolic liver diseases. Despite recent progress, the precise mechanisms remain incompletely understood. Employing excessive exposure to palmitate in hepatocytes as our primary experimental model and mice studies, we aimed to uncover the mechanisms behind hepatic lipotoxicity, thereby developing potential treatments. Our data reveal for the first time that exposure to palmitate leads to downregulated expression of poly(ADP-ribose) polymerase 1 (PARP-1) in hepatocytes, inhibiting its enzymatic activity. While inhibiting PARP-1 worsens palmitate-induced hepatotoxicity, preventing PARP-1 suppression, using NAD⁺ precursors, nicotinamide N-methyltransferase (NNMT) inhibitors, or a poly(ADP-ribose) glycohydrolase (PARG) inhibitor, prevents it. Moreover, we uncover that PARP-1 suppression contributes to palmitate-triggered mTORC1 activation, which has been previously reported by us to contribute to palmitate-induced hepatocyte cell death. Furthermore, our results identify p300 as a downstream target of mTORC1 activation upon palmitate exposure. Importantly, p300 inhibition via either pharmacological or genetic approaches protects against palmitate hepatotoxicity. Additionally, we provide evidence that the TLR4-NF-κB pathway activation in response to palmitate plays a mechanistic role in mediating palmitate-induced PARP-1 downregulation in that both TLR4 antagonist and NF-κB inhibitors prevent palmitate induced PARP-1 reduction and protect against hepatocyte cell death. In conclusion, our study presents new evidence that the PARP-1-mTORC1-p300 pathway serves as a novel molecular mechanism underlying palmitate-induced hepatic lipotoxicity. Targeting the PARP-1 pathway by increasing cellular NAD⁺ availability either through its precursor supplementation or by inhibiting its degradation represents a promising therapeutic approach for treating hepatic lipotoxicity.