Diurnal Regulation of MTP and Plasma Triglyceride by CLOCK Is Mediated by SHP

SummaryWe examined the role of clock genes in the diurnal regulation of plasma triglyceride-rich apolipoprotein B-lipoproteins and their biosynthetic chaperone, microsomal triglyceride transfer protein (MTP). Clockmt/mt mice showed sustained hypertriglyceridemia and high MTP expression. CLOCK knockdown activated MTP promoter and reduced small heterodimer partner (SHP, NROB2). CLOCK upregulated SHP by binding to its E box. SHP suppressed MTP expression by binding to the HNF4α/LRH-1 at the MTP promoter. Cyclic expression of MTP after serum shock was abrogated by siCLOCK and siSHP. Plasma triglyceride and MTP showed reduced diurnal variations in Shp−/− mice. Whereas peaks and nadirs in SHP expression were inversely correlated with those of MTP, these changes were reduced in Clockmt/mt mice. Expression of Shp abrogated hypertriglyceridemia in Clockmt/mt mice. Together, these studies describe a role of Clock/Shp in the diurnal regulation of MTP and plasma triglyceride and indicate that disruptions in circadian regulation might cause hyperlipidemia.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (98 K)Download as PowerPoint slideHighlights► Plasma triglyceride and tissue MTP activity show circadian changes ► These circadian changes are absent in Clock mutant mice ► Clock regulates MTP and plasma triglyceride via SHP ► Overexpression of SHP avoids hypertriglyceridemia in Clock mutant mice