CHL1 promotes insulin secretion and negatively regulates the proliferation of pancreatic β cells.

Cell adhesion molecule L1-like protein (CHL1) is a member of neural recognition molecules of immunoglobulin superfamily primarily expressing in the nervous system. CHL1 regulates neuronal migration, axonal growth, and dendritic projection. Downregulation of CHL1 has been reported in β cells of patients with type 2 diabetes (T2DM). However, the detailed role of CHL1 in β cells has not been characterized. In this study, Real-Time PCR and Western blot were applied to investigate the tissue/cell distribution and expression of CHL1. Gain- or loss-of function studies were conducted in MIN6 cells to determine the effects of CHL1 on cell proliferation, apoptosis, cell cycle, and insulin secretion. Following silencing of CHL1 in MIN6 cells (si-CHL1), insulin secretion and the number of insulin secretary granules <50 nm from the cell membrane decreased in response to 20 mM glucose. Besides, silencing of CHL1 induced cell proliferation, reduced apoptosis, and prolonged S phase and shortened G1 phase of the cell cycle, contrary to overexpressing of CHL1. The inhibitor of ERK1/2MAPK eliminated the effect of CHL1 deficiency on the proliferation of MIN6 cells. In addition, high-fat diet could result in increased islet volume and β cell proliferation, decreased CHL1 expression and activation of ERK pathway in mice islets. Consequently, CHL1 expression was decreased in islets of high-fat induced mice, which resulted in cell proliferation via ERK pathway and regulation of the cell cycle through p53 pathway. These mechanisms may contribute to pancreatic β cell compensatory hyperplasia in obesity-induced pre-diabetes.