Exendin-4 stimulates autophagy in pancreatic β-cells via the RAPGEF/EPAC-Ca²⁺-PPP3/calcineurin-TFEB axis

Abstract

Macroautophagy/autophagy is critical for the regulation of pancreatic β-cell mass and its deregulation has been implicated in the pathogenesis of type 2 diabetes (T2D). We have previously shown that treatment of pancreatic β-cells with the GLP1R (glucagon like peptide 1 receptor) agonist exendin-4 stimulates autophagic flux in a setting of chronic nutrient excess. The aim of this study was to identify the underlying pathways contributing to enhanced autophagic flux.Pancreatic β-cells (INS-1E),mouse and human islets were treated with glucolipotoxic stress (0.5 mM palmitate and 25 mM glucose) in the presence of exendin-4. Consistent with our previous work, exendin-4 stimulated autophagic flux. Using chemical inhibitors and siRNA knockdown, we identified RAPGEF4/EPAC2 (Rap guanine nucleotide exchange factor 4) and downstream calcium signaling to be essential for regulation of autophagic flux by exendin-4. This pathway was independent of AMPK and MTOR signaling. Further analysis identified PPP3/calcineurin and its downstream regulator TFEB (transcription factor EB) as key proteins mediating exendin-4 induced autophagy. Importantly, inhibition of this pathway prevented exendin-4-mediated cell survival and overexpression of TFEB mimicked the cell protective effects of exendin-4 in INS-1E and human islets. Moreover, treatment of db/db mice with exendin-4 for 21 days increased the expression of lysosomal markers within the pancreatic islets. Collectively our data identify the RAPGEF4/EPAC2-calcium-PPP3/calcineurin-TFEB axis as a key mediator of autophagic flux, lysosomal function and cell survival in pancreatic β-cells. Pharmacological modulation of this axis may offer a novel therapeutic target for the treatment of T2D.

Exendin-4 Attenuates Hepatic Steatosis by Promoting the Autophagy-Lysosomal Pathway

“…Exendin-4 has been shown to induce autophagy in many type of cells, including cardiomyocytes [31], pancreatic βcells [32], and ovarian cancer cells [33]. In this study, we found that exendin-4 also induces autophagy in HepG2 cells (Figures 1 and 2); however, the underlying mechanisms remain to be determined.…”

“…In this study, we found that exendin-4 also induces autophagy in HepG2 cells (Figures 1 and 2); however, the underlying mechanisms remain to be determined. Based on other reports, exendin-4 might induce autophagy via mTOR-dependent or mTOR-independent pathways [31,32].…”

Mitophagy and mitochondrial dynamics in type 2 diabetes mellitus treatment

“…Research revealed that a lysosomal associated membrane protein-1 (LAMP1) deficient mice impaired autophagic flux. The impaired autophagy flux triggered aggregations of damaged mitochondria and oxidative stress, and eventually causing progressive beta-cell apoptosis and failure [ 108 , 109 ]. Besides, the regulator of lysosomal genes, TFEB also activated the downstream antioxidant pathway such as nuclear factor E2-related factor 2 (Nrf 2) [ 110 ].…”

Sex-specific transcriptional rewiring in the brain of Alzheimer’s disease patients

“…Another switch gene, LAMA2, is a serum protein biomarker for pre-diabetes ( Yang et al, 2021 ) and is implicated in high-fat diet-induced obesity ( Chen H. J. et al, 2022 ). ADCY1, RAB3A, and RAPGEF4 switch genes identified in F-asymAD play a key role in pancreatic β-cell insulin secretion ( Arora et al, 2012 ; Kitaguchi et al, 2013 ; Gucek et al, 2019 ; Zummo et al, 2022 ). Mutations in ABCC8 are associated with maturity-onset diabetes of the young (MODY) ( Zhang Y. et al, 2022 ), neonatal diabetes ( Lyra et al, 2022 ), and severe congenital hyperinsulinism ( Reyes Diaz et al, 2022 ).…”