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E3 ligase substrate adaptor SPOP fine tunes the UPR of pancreatic beta cells

ABSTRACT: The Cullin-3 E3 ligase adaptor protein, SPOP, targets proteins for ubiquitination and proteasomal degradation. We previously established the β cell transcription factor (TF) and human diabetes gene PDX1 as an SPOP substrate, suggesting a functional role for SPOP in the β cell. Here, we generated a β cell specific Spop deletion mouse strain (SpopβKO) and found that Spop is necessary to prevent aberrant basal insulin secretion and for maintaining glucose- stimulated insulin secretion (GSIS) through impacts on glycolysis and glucose-stimulated calcium flux. Integration of proteomic, TF-regulatory gene network and biochemical analyses identified XBP1 as a functionally important SPOP substrate in pancreatic β cells. Further, loss of SPOP strengthened the IRE1α-XBP1 axis of unfolded protein response (UPR) signaling. ER stress promoted proteasomal degradation of SPOP, supporting a model whereby SPOP fine-tunes XBP1 activation during the UPR. These results position SPOP as a regulator of β cell function and proper UPR activation.

ORGANISM(S): Mus musculus

PROVIDER: GSE282084 | GEO | 2024/12/02

REPOSITORIES: GEO

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E3 ligase substrate adaptor SPOP fine tunes the UPR of pancreatic beta cells

Project description:The Cullin 3 E3 ligase adaptor protein, SPOP, targets proteins for ubiquitination and proteasomal degradation. We previously established the β cell transcription factor (TF) and human diabetes gene PDX1 as an SPOP substrate, suggesting a functional role for SPOP in the β cell. Here, we generated a β cell specific Spop deletion mouse strain (SpopβKO) and found that Spop is necessary to prevent aberrant basal insulin secretion and for maintaining glucose- stimulated insulin secretion (GSIS) through impacts on glycolysis and glucose-stimulated calcium flux. Integration of proteomic, TF-regulatory gene network and biochemical analyses identified XBP1 as a functionally important SPOP substrate in pancreatic β cells.Further, loss of SPOP strengthened the IRE1α-XBP1 axis of unfolded protein response (UPR) signaling. ER stress promoted proteasomal degradation of SPOP, supporting a model whereby SPOP fine-tunes XBP1 activation during the UPR. These results position SPOP as a regulatorof β cell function and proper UPR activation.

2024-11-12 | PXD052527 | Pride

Pancreas-specific Sirt1-deficiency in mice compromises beta-cell function without development of hyperglycemia

Project description:Sirtuin 1 (Sirt1) has been reported to be a critical positive regulator of glucose-stimulated insulin secretion in pancreatic beta-cells. The effects on islet cells and blood glucose levels when Sirt1 is deleted specifically in the pancreas are still unclear.This study examined islet glucose responsiveness, blood glucose levels, pancreatic islet histology and gene expression in Pdx1-Cre;Sirt1(ex4F/F) mice that have loss of function and loss of expression of Sirt1 specifically in the pancreas. We found that in the Pdx1-Cre;Sirt1(ex4F/F) mice, the relative insulin positive area and the islet size distribution were unchanged. However, beta-cells were functionally impaired, presenting with lower glucose-stimulated insulin secretion. This defect was not due to a reduced expression of insulin but was associated with a decreased expression of the glucose transporter Slc2A2/Glut2 and of the Glucagon like peptide-1 receptor (Glp1r) as well as with a marked down regulation of endoplasmic reticulum (ER) chaperones that participate in the Unfolded Protein Response (UPR) pathway. Counter intuitively, the Sirt1-deficient mice did not develop hyperglycemia. Pancreatic polypeptide (PP) cells were the only other islet cells affected, with reduced numbers in the Sirt1-deficient pancreas. This study provides new mechanistic insights showing that beta-cell function in Sirt1-deficient pancreas is affected due to altered glucose sensing and deregulation of the UPR pathway. Interestingly, we uncover a context in which impaired beta-cell function is not accompanied by increased glycemia. This points to a unique compensatory mechanism. Given the reduction in PP, investigation of its role in the control of blood glucose is warranted. To uncover other Sirt1-regulated mechanisms, we performed a gene expression microarray analysis comparing pancreata from the 6 month old Sirt1âdeficient mice to their controls (n=3 per group).

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β-cell-specific deletion of Zfp148 improves nutrient-stimulated β-cell Ca2+ responses

Project description:Insulin secretion from pancreatic β-cells is essential for glucose homeostasis. An insufficient response to the demand for insulin results in diabetes. We previously showed that β-cell-specific deletion of Zfp148 (β-Zfp148KO) improves glucose tolerance and insulin secretion in mice. These RNA sequencing data show pathways altered in the β-Zfp148KO consistent with altered PEP cycling and improved insulin secretion responses.

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Pancreas-specific Sirt1-deficiency in mice compromises beta-cell function without development of hyperglycemia

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E3 ligase substrate adaptor SPOP fine tunes the UPR of pancreatic beta cells

Project description:E3 ligase substrate adaptor SPOP fine tunes the UPR of pancreatic beta cells

| PRJNA1186973 | ENA

A Single-cell Transcriptomic Atlas of Primate Pancreatic Islet Aging

Project description:Aging-related degeneration of pancreatic islet cells contributes to impaired glucose tolerance and diabetes. Endocrine cells age heterogeneously, complicating the effort to unravel the molecular drives underlying endocrine aging. To overcome these obstacles, we undertook single-cell RNA sequencing of pancreatic islet cells obtained from young and aged non-diabetic cynomolgus monkeys. Despite sex differences and increased single-cell level transcriptional variations, aged β-cells showed increased unfolded protein response (UPR) along with the accumulation of protein aggregates. We observed transcriptomic dysregulation of UPR components linked to canonical ATF6 and IRE1 signaling, comprising adaptive UPR during pancreatic aging. Notably, we found age-related β-cell-specific upregulation of HSP90B1, an ER-located chaperone, impeded high glucose-induced insulin secretion. Our work decodes aging-associated transcriptomic changes that underlie pancreatic islet functional decay at the single-cell resolution and indicates that targeting UPR components may prevent loss of proteostasis, suggesting an avenue for therapies to delay β-cell aging and prevent aging-related diabetes.

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