Long non-coding RNAs (lncRNAs) are emerging as crucial regulators of beta cell function. Here, we show that an lncRNA-transcribed antisense to Pax6, annotated as Pax6os1/PAX6-AS1, was upregulated by high glucose concentrations in human as well as murine beta cell lines and islets. Elevated expression was also observed in islets from mice on a high-fat diet and patients with type 2 diabetes. Silencing Pax6os1/PAX6-AS1 in MIN6 or EndoC-βH1 cells increased several beta cell signature genes' expression. Pax6os1/PAX6-AS1 was shown to bind to EIF3D, indicating a role in translation of specific mRNAs, as well as histones H3 and H4, suggesting a role in histone modifications. Important interspecies differences were found, with a stronger phenotype in humans. Only female Pax6os1 null mice fed a high-fat diet showed slightly enhanced glucose clearance. In contrast, silencing PAX6-AS1 in human islets enhanced glucose-stimulated insulin secretion and increased calcium dynamics, whereas overexpression of the lncRNA resulted in the opposite phenotype.
© 2024 The Authors.

Summary Incretin mimetic drugs are in widespread use for the treatment of type 2 diabetes and obesity and more recently have been prescribed for weight loss in otherwise healthy individuals. These drugs are all agonists of the glucagon-like peptide 1 receptor (GLP-1R) and function by supplementing effects produced by the endogenous hormone agonist glucagon-like peptide 1 (GLP-1). The therapeutic benefits of these medications, including improved glucose control and weight loss, require continued usage and wane with time. The molecular mechanisms underlying this loss of effect to incretin drugs remain unknown. Following activation by agonist and signaling to G protein, the GLP-1R engages arrestins and is endocytosed. Here we investigated the role of G protein-coupled receptor associated sorting protein 1 (GASP1), a critical regulator of the post-endocytic trafficking of GLP-1R, on tolerance to GLP-1R agonist drug. We found that tolerance to incretin drug was prevented at the cellular, tissue and whole animal level in mice with a selective disruption of the GASP1 protein in beta cells of the pancreatic islet. These studies implicate post-endocytic sorting of the GLP-1R in the loss of effectiveness of incretin therapeutics with prolonged use. These findings also suggest a novel strategy to prevent tolerance by biasing incretin drugs for G protein and away from arrestin engagement.

The increase in bone mineral content (BMC) and density (BMD) measured by dual-energy x-ray absorptiometry (DXA) in obese children may not sustain the mechanical load associated with weight, and the factors influencing bone mineralization are not well known.
We described bone mineralization in boys with overweight/obesity and leanness in relation to body composition.
Cross-sectional study in the Pediatric Endocrinology Unit of Angers University Hospital with 249 overweight/obese boys aged 8-18 who underwent DXA and insulin, testosterone, and IGF-1 measurements. Bone mineralization was compared with data from 301 lean boys of similar age and height from NHANES 2011-2015, using the same DXA model. Path analyses were performed to evaluate factors associated with total body less head (TBLH) BMC.
The mean age- and height-adjusted difference in TBLH BMC between obese and lean boys was 241 ± 20 g/cm2. Each 1 kg/m2 increase in BMI was associated with +39 ± 6 g of TBLH BMC in lean subjects vs + 25 ± 3 g in obese subjects (P < .05). Each 1 kg/m2 increase in lean BMI (LBMI) was associated with +78 ± 5 g of TBLH BMC in lean and obese boys, and each 1 kg/m2 increase in fat mass index (FMI) was associated with a decrease of 9 ± 3 g of TBLH BMC. The TBLH BMC was directly positively influenced by LBMI and indirectly and positively influenced by IGF-1, testosterone, and insulin (mediated through height and LBMI). FMI indirectly influenced TBLH BMC, both positively through LBMI and negatively through its negative impact on IGF-1 and testosterone.
The increase in bone mineralization in obese children does not adapt to the increase in body mass.
© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society.

Aggregation of human islet amyloid polypeptide (hIAPP), a β-cell secretory product, leads to islet amyloid deposition, islet inflammation and β-cell loss in type 2 diabetes (T2D), but the mechanisms that underlie this process are incompletely understood. Receptor interacting protein kinase 3 (RIPK3) is a pro-death signaling molecule that has recently been implicated in amyloid-associated brain pathology and β-cell cytotoxicity. Here, we evaluated the role of RIPK3 in amyloid-induced β-cell loss using a humanized mouse model of T2D that expresses hIAPP and is prone to islet amyloid formation.
We quantified amyloid deposition, cell death and caspase 3/7 activity in islets isolated from WT, Ripk3-/-, hIAPP and hIAPP; Ripk3-/- mice in real time, and evaluated hIAPP-stimulated inflammation in WT and Ripk3-/- bone marrow derived macrophages (BMDMs) in vitro. We also characterized the role of RIPK3 in glucose stimulated insulin secretion (GSIS) in vitro and in vivo. Finally, we examined the role of RIPK3 in high fat diet (HFD)-induced islet amyloid deposition, β-cell loss and glucose homeostasis in vivo.
We found that amyloid-prone hIAPP mouse islets exhibited increased cell death and caspase 3/7 activity compared to amyloid-free WT islets in vitro, and this was associated with increased RIPK3 expression. hIAPP; Ripk3-/- islets were protected from amyloid-induced cell death compared to hIAPP islets in vitro, although amyloid deposition and caspase 3/7 activity were not different between genotypes. We observed that macrophages are a source of Ripk3 expression in isolated islets, and that Ripk3-/- BMDMs were protected from hIAPP-stimulated inflammatory gene expression (Tnf, Il1b, Nos2). Following 52 weeks of HFD feeding, islet amyloid-prone hIAPP mice exhibited impaired glucose tolerance and decreased β-cell area compared to WT mice in vivo, whereas hIAPP; Ripk3-/- mice were protected from these impairments.
In conclusion, loss of RIPK3 protects from amyloid-induced inflammation and islet cell death in vitro and amyloid-induced β-cell loss and glucose intolerance in vivo. We propose that therapies targeting RIPK3 may reduce islet inflammation and β-cell loss and improve glucose homeostasis in the pathogenesis of T2D.
Published by Elsevier GmbH.

The Rab27 effectors are known to play versatile roles in regulated exocytosis. In pancreatic beta cells, exophilin-8 anchors granules in the peripheral actin cortex, whereas granuphilin and melanophilin mediate granule fusion with and without stable docking to the plasma membrane, respectively. However, it is unknown whether these coexisting effectors function in parallel or in sequence to support the whole insulin secretory process. Here, we investigate their functional relationships by comparing the exocytic phenotypes in mouse beta cells simultaneously lacking two effectors with those lacking just one of them. Analyses of prefusion profiles by total internal reflection fluorescence microscopy suggest that melanophilin exclusively functions downstream of exophilin-8 to mobilize granules for fusion from the actin network to the plasma membrane after stimulation. The two effectors are physically linked via the exocyst complex. Downregulation of the exocyst component affects granule exocytosis only in the presence of exophilin-8. The exocyst and exophilin-8 also promote fusion of granules residing beneath the plasma membrane prior to stimulation, although they differentially act on freely diffusible granules and those stably docked to the plasma membrane by granuphilin, respectively. This is the first study to diagram the multiple intracellular pathways of granule exocytosis and the functional hierarchy among different Rab27 effectors within the same cell.
© 2023, Zhao et al.