Involvement of senescence marker protein-30 in glucose metabolism disorder and non-alcoholic fatty liver disease.

Senescence marker protein-30 (SMP30) was found to decrease in the liver, kidneys and lungs of mice during aging. SMP30 is a pleiotropic protein that acts to protect cells from apoptosis by enhancing plasma membrane Ca(2+) -pump activity and is bona fide gluconolactonase (EC 3.1.1.17) that participates in the penultimate step of the vitamin C biosynthetic pathway. For the past several years, we have obtained strong evidence showing the close relationship between SMP30, glucose metabolism disorder and non-alchoholic fatty liver disease in experiments with SMP30 knockout mice. Emerging proof links the following abnormalities: (i) the reduction of SMP30 by aging and/or excessive dietary fat or genetic deficiency causes a loss of Ca(2+) pumping activity, which impairs acute insulin release in pancreatic β-cells, initiates inflammatory responses with oxidative stress and endoplasmic reticulum stress in non-alchoholic steatohepatitis, exacerbates renal tubule damage, and introduces tubulointerstitial inflammation and fibrosis in diabetic nephropathy; (ii) vitamin C insufficiency also impairs acute insulin secretion in pancreatic β-cells by a mechanism distinct from that of the SMP30 deficiency; and (iii) the increased oxidative stress by concomitant deficiencies of SMP30, superoxide dismutase 1 and vitamin C similarly causes hepatic steatosis. Here, we review recent advances in our understanding of SMP30 in glucose metabolism disorder and non-alchoholic fatty liver disease.