ApoA-I Protects Pancreatic β-Cells From Cholesterol-Induced Mitochondrial Damage and Restores Their Ability to Secrete Insulin

Abstract

Background: High cholesterol levels in pancreatic β-cells cause oxidative stress and decrease insulin secretion. β-cells can internalize apo (apolipoprotein) A-I, which increases insulin secretion. This study asks whether internalization of apoA-I improves β-cell insulin secretion by reducing oxidative stress. Methods: Ins-1E cells were cholesterol-loaded by incubation with cholesterol-methyl-β-cyclodextrin. Insulin secretion in the presence of 2.8 or 25 mmol/L glucose was quantified by radioimmunoassay. Internalization of fluorescently labeled apoA-I by β-cells was monitored by flow cytometry. The effects of apoA-I internalization on β-cell gene expression were evaluated by RNA sequencing. ApoA-I-binding partners on the β-cell surface were identified by mass spectrometry. Mitochondrial oxidative stress was quantified in β-cells and isolated islets with MitoSOX and confocal microscopy. Results: An F 1 -ATPase β-subunit on the β-cell surface was identified as the main apoA-I-binding partner. β-cell internalization of apoA-I was time-, concentration-, temperature-, cholesterol-, and F 1 -ATPase β-subunit-dependent. β-cells with internalized apoA-I (apoA-I + cells) had higher cholesterol and cell surface F 1 -ATPase β-subunit levels than β-cells without internalized apoA-I (apoA-I − cells). The internalized apoA-I colocalized with mitochondria and was associated with reduced oxidative stress and increased insulin secretion. The IF 1 (ATPase inhibitory factor 1) attenuated apoA-I internalization and increased oxidative stress in Ins-1E β-cells and isolated mouse islets. Differentially expressed genes in apoA-I + and apoA-I − Ins-1E cells were related to protein synthesis, the unfolded protein response, insulin secretion, and mitochondrial function. Conclusions: These results establish that β-cells are functionally heterogeneous, and apoA-I restores insulin secretion in β-cells with elevated cholesterol levels by improving mitochondrial redox balance.

Anti-inflammatory mechanism of Apolipoprotein A-I

“…Based on the available research, the regulation of the anti-inflammatory function of immune cells by ApoA-I may be achieved through the following molecular mechanisms: First, ApoA-I causes cholesterol efflux from immune cells to affect the expression of related factors. ApoA-I has a powerful cholesterol transporter function, it can modulate cellular biological functions by altering the cholesterol in cells, as previously demonstrated, the regulation of cholesterol in arterial vascular endothelial cells ( 60 ), and the recently discovered of regulation in pancreatic islet cells ( 61 ). ApoA-I has the same cholesterol-transporting effect in immune cells ( 62 ).…”

New Player in an Old Field? Ecto-F 1 -ATPase in Antidiabetic Actions of HDL in Pancreatic β-Cells

“…The article by Manandhar et al 24 published in this issue of Arteriosclerosis, Thrombosis, and Vascular Biology provides new insights into the mechanisms of action of HDL and apoA-I in β-cells. This work is relevant to T2D, a disorder that is characterized by progressive β-cell dysfunction and the loss of β-cell mass.…”