Filamentous actin (F-actin) cytoskeletal remodeling is critical for glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells, and its dysregulation causes type 2 diabetes. The adaptor protein APPL1 promotes first-phase GSIS by up-regulating soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein expression. However, whether APPL2 (a close homology of APPL1 with the same domain organization) plays a role in β-cell functions is unknown. Here, we show that APPL2 enhances GSIS by promoting F-actin remodeling via the small GTPase Rac1 in pancreatic β-cells. β-cell specific abrogation of APPL2 impaired GSIS, leading to glucose intolerance in mice. APPL2 deficiency largely abolished glucose-induced first- and second-phase insulin secretion in pancreatic islets. Real-time live-cell imaging and phalloidin staining revealed that APPL2 deficiency abolished glucose-induced F-actin depolymerization in pancreatic islets. Likewise, knockdown of APPL2 expression impaired glucose-stimulated F-actin depolymerization and subsequent insulin secretion in INS-1E cells, which were attributable to the impairment of Ras-related C3 botulinum toxin substrate 1 (Rac1) activation. Treatment with the F-actin depolymerization chemical compounds or overexpression of gelsolin (a F-actin remodeling protein) rescued APPL2 deficiency-induced defective GSIS. In addition, APPL2 interacted with Rac GTPase activating protein 1 (RacGAP1) in a glucose-dependent manner via the bin/amphiphysin/rvs-pleckstrin homology (BAR-PH) domain of APPL2 in INS-1E cells and HEK293 cells. Concomitant knockdown of RacGAP1 expression reverted APPL2 deficiency-induced defective GSIS, F-actin remodeling, and Rac1 activation in INS-1E cells. Our data indicate that APPL2 interacts with RacGAP1 and suppresses its negative action on Rac1 activity and F-actin depolymerization thereby enhancing GSIS in pancreatic β-cells. Significance Dysregulation of cytoskeletal remodeling could result in defective GSIS and cause type 2 diabetes. Previous studies have reported the role of small GTPases including Rac1 and Cdc42 in the regulation of F-actin remodeling, whereas the upstream regulatory pathway remains poorly understood. Here, we identify the adaptor protein APPL2 as an upstream regulator of Rac1 activation. APPL2 promotes F-actin remodeling by antagonizing the inhibitory effect of RacGAP1 on Rac1 activation, which eventually enhances GSIS. Our findings fill the overall puzzle of F-actin remodeling with a crucial piece and provide insights into type 2 diabetes with disrupted actin dynamics.

Defective glucose-stimulated insulin secretion (GSIS) and β-cell senescence are hallmarks in diabetes. The mitochondrial enzyme pyruvate carboxylase (PC) has been shown to promote GSIS and β-cell proliferation in the clonal β-cell lines, yet its physiological relevance remains unknown. Here, we provide animal and human data showing a role of PC in protecting β-cells against senescence and maintaining GSIS under different physiological and pathological conditions. β-cell-specific deletion of PC impaired GSIS and induced β-cell senescence in the mouse models under either a standard chow diet or prolonged high-fat diet feeding. Transcriptomic analysis indicated that p53-related senescence and cell cycle arrest are activated in PC-deficient islets. Overexpression of PC inhibited hyperglycemia- and aging-induced p53-related senescence in human and mouse islets as well as INS-1E β-cells, whereas knockdown of PC provoked senescence. Mechanistically, PC interacted with MDM2 to prevent its degradation via the MDM2 binding motif, which in turn restricts the p53-dependent senescent program in β-cells. On the contrary, the regulatory effects of PC on GSIS and the tricarboxylic acid (TCA) anaplerotic flux are p53-independent. We illuminate a function of PC in controlling β-cell senescence through the MDM2–p53 axis.

Background: Pancreatic β‐cells function deteriorates during aging, leading to increased risk of type 2 diabetes. We and others previously demonstrated that p53 activation triggers β‐cell senescence and dysfunction in aging, but how its activity is controlled remains incompletely understood. Metabolites are not only by‐products of metabolic pathways but also function as messengers to regulate various biological pathways. Taurine, a non‐proteinogenic amino acid derived from cysteine, has demonstrated anti‐aging effects in multiple cell types and tissues. Nevertheless, its role in β‐cell senescence remains unclear.Methods: Untargeted metabolomic analysis was used to determine differential metabolites in pancreatic islets of mice during aging. In vitro, β‐cell lines MIN6 and INS‐1E were treated with taurine and its transporter inhibitor, followed by measurement of senescence‐related markers. Multiple experimental techniques, such as LC–MS/MS, co‐immunoprecipitation, DARTS analysis, and LiP‐MS, were used to study the mechanistic actions of taurine.Results: Untargeted metabolomic analysis showed that taurine and taurocholic acid were significantly upregulated in aged islets. Pretreatment with taurine inhibited naturally aging, chemically induced senescent and inflammatory program, oxidative stress, and defective insulin secretion in pancreatic β‐cells. SLC6A6 transporter was required to mediate exogenous taurine uptake, and inhibition of SLC6A6 abolished the anti‐senescent effects of taurine. Taurine bound with CKDN2AIP and inhibited its interaction with p53, thereby promoting p53 degradation and suppressing the p53‐dependent senescent program.Conclusion: Our findings suggest that increasing β‐cell taurine uptake might be a feasible approach to preserve β‐cell function by targeting the p53‐dependent senescent response.

Metabolic-dysfunction-associated steatotic liver disease (MASLD) encompasses a spectrum of pathogenic conditions ranging from steatosis, inflammation, and fibrosis with limited treatment options. We previously demonstrated an upregulation of hepatic murine double minute 2 (MDM2) in human subjects with MASLD. Genetic deletion of hepatic MDM2 and pharmacological inhibition of systemic MDM2 improves steatosis and fibrosis in MASLD mouse models. In this study, we further developed and investigated the therapeutic potential of a hepatocyte-specific triantennary N-acetylgalactosamine (GalNAc)-conjugated antisense oligonucleotide targeting MDM2 (GalNAc-Mdm2ASO) in two distinct dietary-induced mouse models of MASLD: a high-fat-high-cholesterol (HFHC) diet and a choline-deficient, L-amino-acid-defined, high-fat diet (CDAHFD). In the HFHC-induced MASLD model, GalNAc-Mdm2ASO not only alleviated liver injury, steatosis, and fibrosis but also improved obesity-related insulin resistance and hyperlipidemia. The hepatoprotective effects of GalNAc-Mdm2ASO treatment were associated with a reduced accumulation of hepatic cholesterol, diacylglycerol, and ceramide, which are known to trigger MASLD. In CDAHFD-induced MASLD mouse model, GalNAc-Mdm2ASO significantly mitigated hepatic inflammation, cholesterol accumulation, and fibrosis but not triglyceride accumulation. Overall, we prove hepatic inhibition of MDM2 using GalNAc-Mdm2ASO as a promising therapeutic agent for MASLD in two rodent models with distinct pathogenesis.