American journal of physiology. Endocrinology and metabolism最新文献

The Nr4a family of transcription factors control expression of genes essential for fuel metabolism and cellular proliferation. The loss of Nr4a1 in the 832/13 INS-1 β-cell line diminishes mitochondrial respiration, decreases ATP production, and impairs glucose stimulated insulin secretion. Nr4a1 overexpression increases β-cell proliferation, and full body Nr4a1 knock out mice have decreased β-cell area. Thus we hypothesize that β-cell Nr4a1 expression plays a critical role in diabetes disease progression. Here we report the effects of β-cell specific Nr4a1 deletion in mice beginning at 3-months of age. While Nr4a1 β-cell specific deletion has no deleterious effect on male mice fed a standard or high fat diet, or on female mice fed a standard chow diet, female mice fed a high fat diet have decreased glucose tolerance, impaired insulin secretion, impaired expression of key glycolytic genes and decreased pancreatic β-cell area. We demonstrate that estrogen is sufficient to induce β-cell Nr4a1 expression.Our data suggest that Nr4a1 is critical for maintaining functional β-cell mass in females as a response to the stress of increased adiposity.

Type 2 diabetes (T2D) involves progressive loss of functional β-cell mass. In a zebrafish insulin-resistant model (zMIR), overnutrition triggers islet inflammation and nocturnal β-cell death. The cell death is prevented by the cyclophilin D (Ppid) inhibitor, cyclosporin A (CsA). Reducing mitochondrial ROS with mito-TEMPO or mitochondrial calcium with Ru360 protects β cells, further implicating the mitochondrial permeability transition pore (mPTP) in β-cell loss. The timing of β-cell death coincides with lower mitochondrial antioxidant gene expression, indicating diurnal mitochondrial vulnerability. Global ppid-/- preserves β-cell mass without altering islet inflammation or macrophage recruitment. Conversely, β-cell-specific PPID re-expression restores-and exacerbates-β-cell loss, which remains CsA-sensitive. These findings identify Ppid as a β-cell-intrinsic mediator of overnutrition-induced β-cell loss.

Dysregulation of glucose and lipid metabolism is closely linked to metabolic diseases such as obesity, diabetes, and diabetic nephropathy, posing serious threats to human health. Orosomucoid (ORM), an acute-phase protein, exhibits diverse biological functions such as immunomodulation, drug transport, and barrier maintenance. Accumulating evidence has recently revealed ORM's critical regulatory role in metabolic processes. Studies indicate that ORM modulates glucose and lipid metabolism through multiple mechanisms, including regulating food intake, attenuating adipose tissue inflammation and fibrosis, inhibiting adipocyte differentiation and hepatic steatosis, and promoting glycogen synthesis. This review systematically examines the regulatory mechanisms of ORM expression under inflammatory and metabolic stress conditions, the effects of ORM on glucose and lipid homeostasis, and its clinical associations with metabolic diseases. These insights could inform innovative strategies for preventing and treating metabolic diseases.

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.

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.

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 activation of nonshivering thermogenesis (NST) in brown adipose tissue (BAT) by environmental cold challenge yields strong metabolic benefit in the face of diet-induced obesity (DIO). Yet, a critical barrier to leveraging brown fat NST for therapeutic use against metabolic disease is that BAT is silenced and inactive at physiological ambient temperature conditions in humans. The mechanisms that govern this silencing process remain poorly understood. Here, we identified a putative BAT-silencing factor, aquaporin-1 (AQP1), in brown fat from wild-type (WT) mice via proteomics analysis. We generated the first BAT-specific AQP1 knockout mice (AQP1-KO) and revealed that AQP1-KO could activate NST under BAT-silencing environmental conditions and that the AQP1-KO mice were significantly protected against DIO and metabolic dysfunction compared with Flox controls. We found that AQP1-KO mice on a high-fat diet (HFD) had reduced weight gain through reductions in fat mass, improved glucose tolerance, and increased whole body energy expenditure compared with Flox control mice. Mechanistically, we show that AQP1 ablation in mice had upregulated gene expression related to the electron transport chain (ETC) and mitochondrial translation contributing to the activation of NST under BAT environmental silenced conditions.NEW & NOTEWORTHY BAT activation is strongly associated with improved metabolic health such as enhanced cardiometabolic profiles. However, the mechanisms that restrict BAT in this state are unknown. We have identified a putative BAT silencer called AQP1 and through the creation of the first BAT-specific AQP1-KO mouse model, demonstrated that these mice have increased energy expenditure and protection against DIO. Thus, AQP1 is a promising therapeutic target for metabolic dysfunction.

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.