American journal of physiology. Endocrinology and metabolism最新文献

Aerobic fitness is associated with greater skeletal muscle insulin sensitivity with regard to glucose uptake. Whether fitness is associated with an improvement in the insulin regulation of adipose tissue lipolysis is unknown. We collated adipose insulin sensitivity, body composition, and fitness data from six of our previously published and two of our unpublished protocols. Adipose tissue insulin resistance index of palmitate (ADIPO-IR_palmitate) data were available for 340 volunteers, and the insulin concentration resulting in a 50% suppression of palmitate rate of appearance (FFA_palmitate IC₅₀) measured using the insulin clamp technique was available for 108 volunteers. Pearson's correlation and multiple linear regression analysis were performed to assess the relationship between the independent variables of aerobic fitness [peak oxygen consumption (V̇o_2peak), mL kg·FFM^-1·min^-1], age, sex, body mass index (BMI), visceral adipose tissue (VAT), body fat, percent body fat, and the dependent variables ADIPO-IR_palmitate and FFA_palmitate IC₅₀. Factors that were univariately correlated (P < 0.001) with ADIPO-IR_palmitate and FFA_palmitate IC₅₀ were BMI, percent body fat, body fat, and VAT. Fitness correlated negatively with ADIPO-IR_palmitate and FFA_palmitate IC₅₀. Stepwise regression analysis showed that fitness independently predicted ADIPO-IR_palmitate and FFA_palmitate IC₅₀ after adjusting for the other significant factors. These findings suggest that aerobic fitness may promote metabolic health through positive effects on adipose tissue. Clinical Trial Registration: NCT00254371; the other protocols were not considered clinical trials at the time they were conducted.NEW & NOTEWORTHY Greater degrees of aerobic fitness are associated with greater insulin-mediated muscle glucose uptake. Insulin regulates adipose tissue lipolysis, whether aerobic fitness affects insulin's ability to regulate lipolysis is unknown. We found that greater fitness is associated with improved adipose tissue insulin responsiveness independent of age, sex, BMI, visceral adipose tissue, body fat (kg), percent body fat, and adipocyte size. This suggests that exercise, if it improves fitness, may improve both adipose tissue and muscle function.

Hashimoto's thyroiditis (HT) is a prevalent autoimmune disease marked by lymphocytic infiltration and progressive destruction of the thyroid gland. The pathogenesis involves cytotoxic T lymphocytes, whereas regulatory T cells (Tregs), identified by the transcription factor Forkhead box P3 (FOXP3), are crucial for maintaining self-tolerance. This study aimed to investigate the composition of HT' lymphocyte infiltrate and the expression of FOXP3 and PD-L1 within HT patients' thyroid tissue, aiming to clarify their roles in this chronically activated immune environment. This cross-sectional study analyzed surgical thyroid specimens from 18 patients with HT and 12 nonautoimmune controls. Immunohistochemistry was used to evaluate the expression of CD4⁺, CD8⁺, CD20⁺, FOXP3, and PD-L1 markers in the tissue. The HT group had significantly higher expression of CD4⁺, CD8⁺, and CD20⁺ lymphocytes. Although CD25⁺ expression was similar between groups, FOXP3 was positive in 100% of HT samples versus only 8.3% of controls. HT was associated with PD-L1 follicular cell expression in both the cytoplasm and cell membrane, a pattern distinct from the predominantly cytoplasmic expression in controls. In conclusion, this study demonstrates that HT involves a dense intrathyroidal infiltrate of effector T cells, B cells, and FOXP3⁺ Treg cells. The higher prevalence of FOXP3 without a corresponding higher prevalence of CD25⁺ suggests a population of chronically activated Tregs within the inflamed gland. The distinct expression pattern of PD-L1 in follicular cells indicates that the PD-1/PD-L1 pathway is actively engaged, possibly as a protective feedback mechanism against autoimmune destruction. These findings help clarify the local immunoregulatory network in HT and highlight Tregs and the PD-1/PD-L1 axis as promising targets for future therapeutic interventions.NEW & NOTEWORTHY This study provides insight into the local immune environment of Hashimoto's thyroiditis by analyzing the lymphocytic infiltrate in thyroid tissue directly. Key novel findings are the increased prevalence of FOXP3⁺ lymphocytes without a corresponding increase in CD25⁺ cells, suggesting a population of chronically activated regulatory T cells. It also identifies a distinct PD-L1 expression pattern in follicular cells (both membrane and cytoplasm), suggesting a protective feedback mechanism against autoimmune attack.

The effects of Roux-en-Y gastric bypass (RYGB) on the gut-brain axis remain poorly understood. This study specifically explores phenotypic changes in vagal afferent neurons in male obese C57BL/6J mice following RYGB. Our results show that RYGB induced the expression of activating transcription factor 3 (Atf3) mRNA-a well-established marker of axonal injury-in a subset of vagal sensory neurons. In addition, RYGB led to a significant reduction in both the proportion of vagal afferents expressing the glucagon-like peptide 1 receptor (GLP1R) and the overall Glp1r mRNA levels in the nodose ganglion. Nerve transection experiments replicated these changes, suggesting that axonal injury alone may account for the observed phenotypic alterations in vagal afferent neurons following RYGB. Electrophysiological recordings further revealed that acute administration of exendin-4, a GLP1R agonist, significantly enhanced afferent vagus nerve firing. Interestingly, this response was notably exaggerated in RYGB animals and those with injured gastric vagus nerves. Collectively, these findings provide both molecular and electrophysiological evidence that RYGB induces vagal neuropathy, characterized by reduced Glp1r expression and heightened sensitivity to GLP1.NEW & NOTEWORTHY Roux-en-Y gastric bypass in obese mice triggered markers of vagal nerve injury, reduced Glp1r-expressing vagal afferents, and lowered Glp1r mRNA in the nodose ganglion. Nerve injury experiments reproduced these effects. Despite reduced receptor expression, GLP1R agonist-evoked vagal firing was exaggerated after RYGB or vagal injury. Overall, the findings indicate RYGB causes vagal neuropathy with diminished Glp1r expression but heightened GLP1 sensitivity.

Enteroendocrine cells (EECs) are specialized cells located throughout the gastrointestinal (GI) tract, where they have an essential role in regulating various physiological processes related to digestion, metabolism, and gut physiology. EECs secrete different hormones in response to food intake and the presence of nutrients in the gut, which regulate digestion, appetite, insulin secretion, and energy balance. One of the most well-studied hormones is glucagon-like peptide-1 (GLP-1), which is produced by L cells in both the small intestine and the colon. Colonic GLP-1-secreting L cells are not immediately exposed to food and are thus less likely to be responsible for the release of GLP-1 that occurs shortly after ingestion of a meal. Here we sought to determine the role of GLP-1 produced from the distal gut, by generating mice with a deletion of the gene encoding proglucagon (Gcg) in the distal gut and analyzed the effects on body weight, glucose metabolism, and gut transit. Deletion of Gcg in the distal gut reduced circulating levels of GLP-1 but did not affect glucose metabolism or insulin levels on a chow diet or body weight gain or glucose metabolism on a Western-style diet. However, we observed that deletion of distal gut GLP-1 resulted in faster small intestinal transit in female but not male mice. We successfully developed a mouse model that can target L cells in the distal gut and demonstrate that GLP-1 from the distal gut is dispensable for weight and glucose regulation, whereas it regulates gut motility in female mice.NEW & NOTEWORTHY Previous studies have suggested that GLP-1 from the distal gut may be of importance for regulation of glucose metabolism although the contribution from ileal and colonic GLP-1 has not been separated. In this study, we established a mouse model to more specifically dissect the role of colonic GLP-1 and demonstrate that the physiological role of GLP-1 from the colon does not include the well-established metabolic functions but rather slows small intestinal transit.

Insulin released in response to a stepwise increase in glucose (square wave) is biphasic with a transient 5-10 min first-phase peak and a more sustained second phase. Although the first phase is generally assumed to be rate-dependent and the second concentration-dependent, detailed studies of first-phase rate sensitivity are lacking. We performed dynamic perifusion studies with human islets using customizable glucose ramps and established the corresponding insulin secretion time profiles. First-phase release was defined as the excess insulin above that expected from the concentration-dependent second phase, and its dependence on the glucose gradient (rate of increase) was examined. The first-phase insulin release rate calculated this way increased with the gradient and fit well to a Hill-type sigmoid function with a half-maximal value around 1.25 mM/min (n_Hill = 1.8, r² = 0.96). This aligns with our previously introduced glucose-insulin control system built on a general framework of a sigmoid proportional-integral-derivative (σPID) controller, a generalized PID controller more suitable for biological systems than linear ones as responses are bounded between zero and a maximum. Experimental results were used to slightly recalibrate this local glucose concentration-based computational model resulting in predictions in good agreement with measured first- and second-phase insulin secretions (r² > 0.90). Thus, glucose-stimulated insulin secretion of perifused human islets can be described well as the sum of a mainly rate-sensitive first phase, which is a sigmoid function of the glucose gradient with half-maximal activation around 1.25 mM/min, and a concentration-sensitive second phase, which is a sigmoid function of the glucose concentration with half-maximal activation near 8 mM.NEW & NOTEWORTHY We performed dynamic perifusion studies of human pancreatic islets with customizable glucose ramps that confirmed that the first phase of glucose-stimulated insulin secretion (GSIS) is rate-sensitive. Overall, we found that GSIS of isolated human islets can be described well as the sum of a rate-dependent first phase and a concentration-dependent second phase characterized by Hill-type sigmoid functions with half-maximal activations at a gradient of 1.25 mM/min and a glucose concentration of 8 mM, respectively.

Although it is well established that animals adapted to a high-protein, carbohydrate-free (HP) diet maintain glycemia through enhanced hepatic gluconeogenesis, the regulatory factors and molecular mechanisms underlying this adaptation remain incompletely understood. Given the chronically elevated glucagon levels observed in these animals, we hypothesized that the cAMP/PKA/CREB signaling pathway might contribute to the enhanced gluconeogenic capacity observed in HP-fed mice. Although CREB activity was transiently increased during early HP feeding, it became attenuated upon prolonged exposure. This attenuation correlated with elevated hepatic GRK2 content, likely driven by increased circulating branched-chain amino acids (BCAAs) and suppression of hepatic autophagy. Exploring alternative regulatory pathways, we identified impaired insulin signaling and reduced phosphorylation and acetylation of hepatic FoxO1 in HP-adapted mice, supporting a central role for FoxO1 in sustaining gluconeogenesis. Consistently, pharmacological inhibition of FoxO1 reduced hepatic gluconeogenesis and glycemia, and suppressed the liver expression of Ppargc1a, Nr4a1, and Hnf4a, key transcriptional coactivators associated with long-term gluconeogenic regulation. Furthermore, we found that elevated corticosterone levels in HP-adapted animals were essential for maintaining hepatic gluconeogenesis and its fasting glycemia. Together, our findings reveal a shift in the regulatory landscape of hepatic gluconeogenesis during HP feeding, transitioning from early CREB activation to a sustained FoxO1-driven transcriptional program.NEW & NOTEWORTHY The regulation of hepatic glucose production under a high-protein (HP) diet remains unclear. We show that gluconeogenesis in HP-fed mice is initially driven by CREB but shifts to FoxO1 dependence over time. Notably, FoxO1 is essential for maintaining gluconeogenesis and glycemia in HP-adapted animals. We also reveal a key role for corticosterone in preserving gluconeogenic capacity and fasting glycemia. These findings provide insights into hepatic metabolic adaptation and into molecular mechanisms governing glycemic homeostasis.

Regulated secretion of insulin from β-cells, glucagon from α-cells, and somatostatin from δ-cells is necessary for the maintenance of glucose homeostasis. The release of these hormones from pancreatic islets requires the assembly and disassembly of the SNARE protein complex to control vesicle fusion. Complexin 2 (Cplx 2) is a small soluble synaptic protein that participates in the priming and release of vesicles. It plays a dual role as a molecular switch that clamps and prevents fusion pore opening, which subsequently undergoes a conformational change upon Ca²⁺ binding to synaptotagmin to facilitate exocytosis. Using a Cplx 2 knockout (KO) mouse model, we show a direct inhibitory role of Cplx 2 for glucagon and somatostatin secretion, along with an indirect role in the paracrine inhibition of insulin secretion by somatostatin. Deletion of Cplx 2 increases glucagon and somatostatin secretion from intact mouse islets, whereas there is no effect on insulin secretion. The normal paracrine inhibition of insulin secretion by somatostatin is disrupted in Cplx 2 KO islets. On the contrary, deletion of Cplx 2 did not affect the paracrine inhibition of glucagon by somatostatin at elevated glucose levels. In both β- and α-cells, the secretion profiles are parallel to Ca²⁺ activity changes following somatostatin treatment of wild-type (WT) and Cplx 2 KO islets. The loss of paracrine inhibition of insulin secretion is substantiated by direct measurements of insulin vesicle fusion events in Cplx 2 KO islets. Together, these data show a differential role for Cplx 2 in regulating hormone secretion from pancreatic islets.NEW & NOTEWORTHY Complexin 2 (Cplx 2) is a small synaptic protein that functions to clamp and release the SNARE protein complex during exocytosis. We show that Cplx 2 has a direct inhibitory role in glucagon and somatostatin secretion from intact mouse islets. Furthermore, the deletion of Cplx 2 leads to disrupted inhibition of β-cell Ca²⁺ activity and insulin secretion by somatostatin. These findings highlight a differential regulatory role of Cplx 2 in hormone secretion from pancreatic islets.

The cyclic adenosine monophosphate (cAMP)-phosphodiesterase 4 (PDE4) family comprises four genes that together are expressed as ∼25 protein variants. Nonselective PAN-PDE4 inhibition exerts various metabolic benefits, including reduced body weight and adiposity in humans and animals, but the role of individual PDE4s in mediating these effects remains ill-defined. We noticed that the hormonal induction of adipogenesis in 3T3-L1 preadipocytes increased the mRNA and protein expression of a single PDE4 variant, PDE4B2. Conversely, its siRNA-mediated knockdown markedly suppressed adipogenic differentiation and lipid accumulation, suggesting a critical role for PDE4B2 in adipogenesis. The onset of adipogenesis is well understood and involves the consecutive upregulation of proadipogenic transcription factors CCAAT-enhancer-binding proteins (C/EBPs) C/EBPδ, C/EBPβ, and C/EBPα, which ultimately induce peroxisome proliferator-activated receptor γ (PPARγ) as the master regulator of adipogenesis. PDE4B knockdown potently suppressed the upregulation of C/EBPα and PPARγ expression, thereby curbing the early steps in adipogenic differentiation. Mirroring its antiadipogenic effects in 3T3-L1 cells, PDE4B ablation in mice produces a lean phenotype characterized by reduced adipose tissue weight and reduced expression of C/EBPα and PPARγ. Although PPARγ agonists promote weight gain, they are also effective insulin sensitizers and are used therapeutically to treat type 2 diabetes. Conversely, despite reducing PPARγ expression and adiposity, PDE4B knockout mice exhibit slightly improved glucose homeostasis. Taken together, we show that a PDE4B-dependent regulation of C/EBPα and PPARγ expression is conserved between cell and animal models. To what extent this mechanism contributes to the overall metabolic phenotypes of targeting PDE4B or PPARγ in vivo remains to be elucidated.NEW & NOTEWORTHY PAN-PDE4 inhibitors exert various metabolic benefits, but gastrointestinal adverse effects have hampered their clinical utility. Targeting individual PDE4 isoforms may lead to drugs with an improved safety profile. Here, we reveal the critical role of one PDE4 isoform, PDE4B2, in the induction of adipogenesis in 3T3-L1 preadipocytes and the regulation of PPARγ expression. The PDE4B-dependent regulation of PPARγ is conserved between cell and animal models and may contribute to the lean phenotype of PDE4B-KO mice.

The Western diet, rich in fats and sugars such as fructose, contributes significantly to the global rise in obesity and type 2 diabetes mellitus. Although both high-fat diets (HFD) and high-fructose diets (HFrD) are known to impair hepatic insulin signaling, the specific mechanisms and potential sex-specific differences remain underexplored. Moreover, the role of hepatic androgen receptor (AR) in modulating these effects, particularly in females, has not been fully elucidated. Here, we investigated the contribution of hepatic AR to HFrD-induced metabolic dysfunction using liver-specific AR knockout (LivARKO) mice of both sexes. Male and female LivARKO and wild-type (WT) littermates were subjected to either a HFrD or calorie-matched control diet from 4 to 12 wk of age and underwent several metabolic tests during months 1 and 2. Glucose tolerance tests (GTT) conducted during month 1 revealed that WT-HFrD females developed significant glucose intolerance, whereas LivARKO-HFrD females exhibited partial protection, demonstrating improved glucose clearance relative to their WT counterparts. These effects appeared sex-specific, as male LivARKO mice did not exhibit similar protective effects under HFrD conditions. Our findings suggest that hepatic AR plays a sex-specific role in mediating fructose-induced insulin resistance, and its deletion in females confers partial protection against diet-induced metabolic impairments by improving hepatic insulin signaling and regulating gluconeogenic genes. This highlights the importance of considering sex and hepatic androgen signaling in the development of targeted therapies for diet-induced metabolic disorders.NEW & NOTEWORTHY To our knowledge, this study is the first to demonstrate that liver-specific androgen receptor (AR) deletion in female mice provides selective protection against fructose-induced insulin resistance. Although hepatic AR loss improves insulin sensitivity, it does not fully preserve insulin secretion or gluconeogenic control, revealing a sex-specific, dichotomous role of hepatic AR in metabolic regulation. These findings highlight hepatic AR as a potential therapeutic target for diet- and androgen-related metabolic dysfunction in females.