Role of TRPV channels in regulating various pancreatic β-cell functions: Lessons from <i>in vitro</i> studies

Background/Aims: Intermittent hypoxia (IH) causes apoptosis in pancreatic β-cells, but the potential mechanisms remain unclear. Endoplasmic reticulum (ER) stress, autophagy, and apoptosis are interlocked in an extensive crosstalk. Thus, this study aimed to investigate the contributions of ER stress and autophagy to IH-induced pancreatic β-cell apoptosis. Methods: We established animal and cell models of IH, and then inhibited autophagy and ER stress by pharmacology and small interfering RNA (siRNA) in INS-1 cells and rats. The levels of biomarkers for autophagy, ER stress, and apoptosis were evaluated by immunoblotting and immunofluorescence. The number of autophagic vacuoles was observed by transmission electron microscopy. Results: IH induced autophagy activation both in vivo and in vitro, as evidenced by increased autophagic vacuole formation and LC3 turnover, and decreased SQSTM1 level. The levels of ER-stress-related proteins, including GRP78, CHOP, caspase 12, phosphorylated (p)-protein kinase RNA-like ER kinase (PERK), p-eIF2α, and activating transcription factor 4 (ATF4) were increased under IH conditions. Inhibition of ER stress with tauroursodeoxycholic acid or 4-phenylbutyrate partially blocked IH-induced autophagy in INS-1 cells. Furthermore, inhibition of PERK with GSK2606414 or siRNA blocked the ERstress-related PERK/eIF2α/ATF4 signaling pathway and inhibited autophagy induced by IH, which indicates that IH-induced autophagy activation is dependent on this signaling pathway. Promoting autophagy with rapamycin alleviated IH-induced apoptosis, whereas inhibition of autophagy with chloroquine or autophagy-related gene (Atg5 and Atg7) siRNA aggravated pancreatic β-cell apoptosis caused by IH. Conclusion: IH induces autophagy activation through the ER-stress-related PERK/eIF2α/ATF4 signaling pathway, which is a protective response to pancreatic β-cell apoptosis caused by IH.

Download Full-text

Honokiol protects pancreatic β cell against high glucose and intermittent hypoxia-induced injury by activating Nrf2/ARE pathway in vitro and in vivo

Biomedicine & Pharmacotherapy ◽

10.1016/j.biopha.2017.11.063 ◽

2018 ◽

Vol 97 ◽

pp. 1229-1237 ◽

Cited By ~ 13

Author(s):

Chen-guang Li ◽

Chang-lin Ni ◽

Min Yang ◽

Yun-zhao Tang ◽

Zhu Li ◽

...

Keyword(s):

High Glucose ◽

Intermittent Hypoxia ◽

Pancreatic Β Cell ◽

Β Cell

Download Full-text

SAD-A, a downstream mediator of GLP-1 signaling, promotes the phosphorylation of Bad S155 to regulate in vitro β-cell functions

Biochemical and Biophysical Research Communications ◽

10.1016/j.bbrc.2018.12.063 ◽

2019 ◽

Vol 509 (1) ◽

pp. 76-81 ◽

Cited By ~ 3

Author(s):

Kai Wang ◽

Dechen Liu ◽

Yaqin Zhang ◽

Xiaoai Chang ◽

Rufeng Xu ◽

...

Keyword(s):

Β Cell ◽

Cell Functions ◽

Downstream Mediator

Download Full-text

Differential activation of ER stress and apoptosis in response to chronically elevated free fatty acids in pancreatic β-cells

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00478.2007 ◽

2008 ◽

Vol 294 (3) ◽

pp. E540-E550 ◽

Cited By ~ 108

Author(s):

Elida Lai ◽

George Bikopoulos ◽

Michael B. Wheeler ◽

Maria Rozakis-Adcock ◽

Allen Volchuk

Keyword(s):

Er Stress ◽

Cell Lines ◽

Cell Apoptosis ◽

Human Islets ◽

Pancreatic Β Cell ◽

Β Cell ◽

Min6 Cells ◽

Relative Contribution ◽

Induced Apoptosis

Chronic exposure to elevated saturated free fatty acid (FFA) levels has been shown to induce endoplasmic reticulum (ER) stress that may contribute to promoting pancreatic β-cell apoptosis. Here, we compared the effects of FFAs on apoptosis and ER stress in human islets and two pancreatic β-cell lines, rat INS-1 and mouse MIN6 cells. Isolated human islets cultured in vitro underwent apoptosis, and markers of ER stress pathways were elevated by chronic palmitate exposure. Palmitate also induced apoptosis in MIN6 and INS-1 cells, although the former were more resistant to both apoptosis and ER stress. MIN6 cells were found to express significantly higher levels of ER chaperone proteins than INS-1 cells, which likely accounts for the ER stress resistance. We attempted to determine the relative contribution that ER stress plays in palmitate-induced β-cell apoptosis. Although overexpressing GRP78 in INS-1 cells partially reduced susceptibility to thapsigargin, this failed to reduce palmitate-induced ER stress or apoptosis. In INS-1 cells, palmitate induced apoptosis at concentrations that did not result in significant ER stress. Finally, MIN6 cells depleted of GRP78 were more susceptible to tunicamycin-induced apoptosis but not to palmitate-induced apoptosis compared with control cells. These results suggest that ER stress is likely not the main mechanism involved in palmitate-induced apoptosis in β-cell lines. Human islets and MIN6 cells were found to express high levels of stearoyl-CoA desaturase-1 compared with INS-1 cells, which may account for the decreased susceptibility of these cells to the cytotoxic effects of palmitate.

Download Full-text

Role of AKT/mTORC1 pathway in pancreatic β-cell proliferation

Colombia Medica ◽

10.25100/cm.v43i3.783 ◽

2012 ◽

pp. 235-243 ◽

Cited By ~ 9

Author(s):

Norman Balcazar Morales ◽

Cecilia Aguilar de Plata

Keyword(s):

Cell Cycle ◽

Growth Factors ◽

Cell Cycle Progression ◽

Cell Mass ◽

Pancreatic Β Cell ◽

Β Cell ◽

Cycle Progression ◽

Mtorc1 Signaling

Growth factors, insulin signaling and nutrients are important regulators of β-cell mass and function. The events linking these signals to regulation of β-cell mass are not completely understood. Recent findings indicate that mTOR pathway integrates signals from growth factors and nutrients with transcription, translation, cell size, cytoskeleton remodeling and mitochondrial metabolism. mTOR is a part of two distinct complexes; mTORC1 and mTORC2. The mammalian TORC1 is sensitive to rapamycin and contains Raptor, deptor, PRAS40 and the G protein β-subunit-like protein (GβL). mTORC1 activates key regulators of protein translation; ribosomal S6 kinase (S6K) and eukaryote initiation factor 4E-binding protein 1. This review summarizes current findings about the role of AKT/mTORC1 signaling in regulation of pancreatic β cell mass and proliferation. mTORC1 is a major regulator of β-cell cycle progression by modulation of cyclins D2, D3 and cdk4/cyclin D activity. These studies uncovered key novel pathways controlling cell cycle progression in β-cells in vivo. This information can be used to develop alternative approaches to expand β-cell mass in vivo and in vitro without the risk of oncogenic transformation. The acquisition of such knowledge is critical for the design of improved therapeutic strategies for the treatment and cure of diabetes as well as to understand the effects of mTOR inhibitors in β-cell function.

Download Full-text