Yunxia Zhu

Background Our group recently reported that a mutation of the novel Beclin1 K414R acetylation site impacts the stability of Beclin1 protein, which decreases autophagy in adipocytes and further impedes adipocyte differentiation and lipolysis. This study was to explore whether Beclin1 acetylation plays a role in the early renal injury induced by high glucose and to further investigate the K414R mutation site in podocytes. Methods Male Sprague–Dawley rats were randomized to con (control) and diabetic nephropathy (DN) groups. The DN group was induced by a single 55 mg/kg intraperitoneal injection of streptozotocin and fed a high-fat and high-sugar diet (the con group received an equal volume of the vehicle and fed a plain diet), after 3 days of induction, blood glucose levels were measured to confirm the onset of diabetes. Then, at weeks 0 and 4, the biochemical index was assayed and renal cortex tissues were harvested. MPC5 podocytes were cultured in vitro. Beclin1 (K414R)-pLVX-ZsGreen1-N1(wild-type or mutant) lentiviral plasmids were transfected into podocytes. Western blot or immunoprecipitation was used to test proteins or the acetylation levels respectively, and immunohistochemistry was used to analyze morphological changes of podocytes. Immunofluorescence was used to detect the aggregation of LC3 puncta. Results The acetylation level of Beclin1 was upregulated with podocyte injury exacerbated in high glucose at 24 h and that a mutation at K414R could inhibit hyperactivated autophagy, which ameliorated podocyte impairment. Conclusion These findings suggest that the acetylation site at K414 is a critical molecule and drug target and that further research into this area is warranted.

Background: Sarcopenia is a geriatric syndrome characterized by progressive loss of muscle mass, function and quality and associated with a range of adverse health outcomes including disability. Despite a negative correlation between muscle mass and follicle-stimulating hormone (FSH) levels in postmenopausal women, it is unclear if FSH is associated with sarcopenia and its poor outcomes, especially in older men.Methods: We used cross-sectional data from 360 men aged over 80 who participated in health check-ups to investigate correlations between serum FSH and sarcopenia, individual sarcopenia components, low physical performance (gait speed ≤ 0.8 m/s) and instrumental activities of daily living (IADL) disability. Sarcopenia and severe sarcopenia were diagnosed according to the revised definition of the European Working Group on Sarcopenia in Old People (EWGSOP2).Results: The prevalence of sarcopenia was 17.8% in this population. In binary logistic regression analysis, compared with higher FSH group, lower FSH group showed a significant reduction in the risk of low calf circumference (a surrogate for muscle mass; OR 0.308, 95% CI 0.109–0.868, P = 0.026) after adjusting potential confounders including age, waist circumference, education, exercise, associated biochemical parameters, other sex hormones and high-sensitivity C-reactive protein. The correlation between FSH and low handgrip strength was marginally significant (OR 0.390, 95% CI 0.151–1.005, P = 0.051). No associations were observed between FSH and sarcopenia, severe sarcopenia, and disability in adjusted models.Conclusion: In older men, circulating FSH was not associated with sarcopenia, sarcopenia severity, the majority of its components and adverse health outcome (IADL disability), with the exception of low calf circumference. Further work is needed to better elucidate the association of FSH and low muscle quantity by adopting more accurate measurement method of appendicular skeletal muscle mass such as DXA, CT or MRI.

Oxidative stress induced by free fatty acid overload in pancreatic β-cells is a potential contributory factor to dysfunction of insulin secretion and apoptotic cell death. Perilipin 5 (Plin5) has been reported to ameliorate oxidative stress-mediated damage in non-insulin-secreting tissues. We tested the hypothesis that Plin5 plays a similar role in pancreatic β-cells, which are extremely sensitive to oxidative stress. Here, our in vitro data showed that Plin5-mediated alleviation of palmitate-triggered apoptosis involves the mitochondrial pathway. And the protective role of Plin5 on β-cells was partially dependent on its modulation in oxidative stress. Upregulation of Plin5 in INS-1 cells decreased reactive oxygen species production, enhanced cellular glutathione levels, and induced expression of antioxidant enzymes glutamate-cysteine ligase catalytic subunit and heme oxygenase-1. However, knocking out of Plin5 abolished all of these beneficial effects. Furthermore, by using the O²⁻ scavenger MnTMPyP, we verified that altering Plin5 expression impacted lipotoxic cell death partially via modulating oxidative stress. Mechanistic experiments revealed that Plin5 induced Nrf2-ARE system, a master regulator in the cellular adaptive response to oxidative stress, by activating PI3K/Akt and ERK signal pathways, contributing to the increase of antioxidant defense and consequently improving β-cell function and survival in the presence of lipotoxic oxidative stress. Overall, our findings indicate that Plin5 abrogates oxidative damage in INS-1 β-cells during lipotoxic stress partially through the enhancement of antioxidant defense involving the PI3K/Akt and ERK mediated Nrf2-ARE system.

Chronic exposure of pancreatic β-cells to excess free fatty acids is thought to contribute to type 2 diabetes pathogenesis in obesity by impairing β-cell function and even leading to apoptosis. In β-cells, lipid droplet-associated protein perilipin 5 (PLIN5) has been shown to enhance insulin secretion by regulating intracellular lipid metabolism; the roles of PLIN5 in response to lipotoxicity remain poorly understood. INS-1 β-cells were transfected with PLIN5-overexpression adenovirus (Ad-PLIN5) and treated with palmitate. C57BL/6 J male mice were fed with high fat diet and tail intravenous injected with adeno-associated virus overexpressing PLIN5 (AAV-PLIN5) in β-cells. Our data showed that palmitate and PPAR agonists including WY14643 (PPARα), GW501516 (PPARβ/δ), rosiglitazone (PPARγ) in vitro all induced PLIN5 expression in INS-1 cells. Under palmitate overload, although upregulating PLIN5 promoted lipid droplet storage, it alleviated lipotoxicity in INS-1 β-cells with improved cell viability, cell apoptosis and β-cell function. The protection role of PLIN5 in β-cell function observed in cell experiments were further verified in in vivo study indicated by mitigated glucose intolerance in high fat diet fed mice with β-cell-specific overexpression of PLIN5. Mechanistic experiments revealed that enhanced FAO induced by elevation of PLIN5, followed by decreased ER stress may be a major mechanism responsible for alleviation of lipotoxicity observed in the present study. Our finding substantiated the important role of PLIN5 in protection against lipotoxicity in β-cells.

Peroxisome proliferator-activated receptor (PPAR) agonists are used for treating hyperglycemia and type 2 diabetes. However, the mechanism of action of these agonists is still under investigation. The lipid droplet-associated proteins FSP27/CIDEC and LSDP5, regulated directly by PPARγand PPARα, are associated with hepatic steatosis and insulin sensitivity. Here, we evaluated the expression levels of FSP27/CIDEC and LSDP5 and the regulation of these proteins by consumption of a high-fat diet (HFD) or administration of PPAR agonists. Mice with diet-induced obesity were treated with the PPARγor PPARαagonist, pioglitazone or fenofibrate, respectively. Liver tissues fromdb/dbdiabetic mice and human were also collected. Interestingly, FSP27/CIEDC was expressed in mouse and human livers and was upregulated in obese C57BL/6J mice. Fenofibrate treatment decreased hepatic triglyceride (TG) content and FSP27/CIDEC protein expression in mice fed an HFD diet. In mice, LSDP5 was not detected, even in the context of insulin resistance or treatment with PPAR agonists. However, LSDP5 was highly expressed in humans, with elevated expression observed in the fatty liver. We concluded that fenofibrate greatly decreased hepatic TG content and FSP27/CIDEC protein expression in mice fed an HFD, suggesting a potential regulatory role for fenofibrate in the amelioration of hepatic steatosis.

Aims/hypothesis Adaptor protein, phosphotyrosine interaction, pleckstrin homology domain and leucine zipper containing 1 (APPL1) is an adapter protein that positively mediates adiponectin signalling. Deficiency of APPL1 in the target tissues of insulin induces insulin resistance. We therefore aimed, in the present study, to determine its role in regulating pancreatic beta cell function. Methods A hyperglycaemic clamp test was performed to determine insulin secretion in APPL1 knockout (KO) mice. Glucose- and adiponectin-induced insulin release was measured in islets from APPL1 KO mice or INS-1(832/13) cells with either APPL1 knockdown or overproduction. RT-PCR and western blotting were conducted to analyse gene expression and protein abundance. Oxygen consumption rate (OCR), ATP production and mitochondrial membrane potential were assayed to evaluate mitochondrial function. Results APPL1 is highly expressed in pancreatic islets, but its levels are decreased in mice fed a high-fat diet and db/db mice compared with controls. Deletion of the Appl1 gene leads to impairment of both the first and second phases of insulin secretion during hyperglycaemic clamp tests. In addition, glucose-stimulated insulin secretion (GSIS) is significantly decreased in islets from APPL1 KO mice. Conversely, overproduction of APPL1 leads to an increase in GSIS in beta cells. In addition, expression levels of several genes involved in insulin production, mitochondrial biogenesis and mitochondrial OCR, ATP production and mitochondrial membrane potential are reduced significantly in APPL1-knockdown beta cells. Moreover, suppression or overexproduction of APPL1 inhibits or stimulates adiponectin-potentiated GSIS in beta cells, respectively. Conclusions/interpretation Our study demonstrates the roles of APPL1 in regulating GSIS and mitochondrial function in pancreatic beta cells, which implicates APPL1 as a therapeutic target in the treatment of type 2 diabetes.

To determine whether smoking increases the risk for developing metabolic syndrome (MetS) in Chinese men.

Background and Aim:  Non‐alcoholic fatty liver disease (NAFLD) is becoming a major public health hazard in China. The present study aimed to estimate the prevalence of NAFLD, NAFLD with abnormal serum alanine aminotransferase (ALT) levels, and determine the potential associations of ALT levels with the components of metabolic syndrome (MetS) in the absence or presence of NAFLD in Chinese adults.Methods:  A population‐based cross‐sectional survey was conducted with 2226 participants. Physical examinations, laboratory tests and hepatic ultrasounds were performed. Individuals were further stratified into higher or lower ALT subgroups with the upper quartiles of ALT in this population. The MetS was identified according to the criteria of the Chinese Joint Committee for Developing Chinese Guidelines (JCDCG).Results:  The standardized prevalence of NAFLD was 23.3% (NAFLD with abnormal ALT levels, 3.1%), 26.5% (NAFLD with abnormal ALT levels, 5.1%) in males, and 19.7% (NAFLD with abnormal ALT levels, 0.9%) in females. Multivariate logistic analysis revealed that higher ALT was significantly associated with elevated triglyceride (TG) in the non‐NAFLD participants, independent of age, smoking status, drinking status, and other MetS‐related measures with odds ratios (95% confidence intervals) of 3.4 (1.6–7.1) and 2.3 (1.4–3.7) in males and females, respectively. On the other hand, the higher ALT was statistically associated with elevated TG and hyperglycemia in the NAFLD cases with odds ratios of 2.2 to 2.5 (P < 0.05).Conclusions:  The prevalence of NAFLD has become epidemic in Shanghai adults. NAFLD combined with ALT levels may be used to identify the individuals at the different risk levels of metabolic disorders.