Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a member of the proteinase K subfamily of subtilases that reduces the number of LDL receptors (LDLRs) in liver through an undefined posttranscriptional mechanism. We show that purified PCSK9 added to the medium of HepG2 cells reduces the number of cellsurface LDLRs in a dose-and time-dependent manner. This activity was approximately 10-fold greater for a gain-of-function mutant, PCSK9(D374Y), that causes hypercholesterolemia. Binding and uptake of PCSK9 were largely dependent on the presence of LDLRs. Coimmunoprecipitation and ligand blotting studies indicated that PCSK9 and LDLR directly associate; both proteins colocalized to late endocytic compartments. Purified PCSK9 had no effect on cell-surface LDLRs in hepatocytes lacking autosomal recessive hypercholesterolemia (ARH), an adaptor protein required for endocytosis of the receptor. Transgenic mice overexpressing human PCSK9 in liver secreted large amounts of the protein into plasma, which increased plasma LDL cholesterol concentrations to levels similar to those of LDLR-knockout mice. To determine whether PCSK9 was active in plasma, transgenic PCSK9 mice were parabiosed with wild-type littermates. After parabiosis, secreted PCSK9 was transferred to the circulation of wild-type mice and reduced the number of hepatic LDLRs to nearly undetectable levels. We conclude that secreted PCSK9 associates with the LDLR and reduces hepatic LDLR protein levels.

PCSK9 encodes proprotein convertase subtilisin͞kexin type 9a (PCSK9), a member of the proteinase K subfamily of subtilases. Missense mutations in PCSK9 cause an autosomal dominant form of hypercholesterolemia in humans, likely due to a gain-of-function mechanism because overexpression of either WT or mutant PCSK9 reduces hepatic LDL receptor protein (LDLR) in mice. Here, we show that livers of knockout mice lacking PCSK9 manifest increased LDLR protein but not mRNA. Increased LDLR protein led to increased clearance of circulating lipoproteins and decreased plasma cholesterol levels (46 mg͞dl in Pcsk9 ؊/؊ mice versus 96 mg͞dl in WT mice). Statins, a class of drugs that inhibit cholesterol synthesis, increase expression of sterol regulatory element-binding protein-2 (SREBP-2), a transcription factor that activates both the Ldlr and Pcsk9 genes. Statin administration to Pcsk9 ؊/؊ mice produced an exaggerated increase in LDLRs in liver and enhanced LDL clearance from plasma. These data demonstrate that PCSK9 regulates the amount of LDLR protein in liver and suggest that inhibitors of PCSK9 may act synergistically with statins to enhance LDLRs and reduce plasma cholesterol.low-density lipoprotein receptor ͉ lipoproteins ͉ proteinase ͉ sterol regulatory element-binding protein

SUMMARY Mutations in 1-acylglycerol-3-phosphate-O-acyltransferase 2 (AGPAT2) cause congenital generalized lipodystrophy. To understand the molecular mechanisms underlying the metabolic complications associated with AGPAT2 deficiency, Agpat2 null mice were generated. Agpat2−/− mice develop severe lipodystrophy affecting both white and brown adipose tissue, severe insulin resistance, diabetes, and hepatic steatosis. The expression of lipogenic genes and rates of de novo fatty acid biosynthesis were increased ~4-fold in Agpat2−/− mouse livers. The mRNA and protein levels of monoacylglycerol acyltransferase isoform 1 were markedly increased in the livers of Agpat2−/− mice suggesting that the alternative monoacylglycerol pathway for triglyceride biosynthesis is activated in the absence of AGPAT2. Feeding a fat-free diet reduced liver triglycerides by ~50% in Agpat2−/− mice. These observations suggest that both dietary fat and hepatic triglyceride biosynthesis via a novel monoacylglycerol pathway may contribute to hepatic steatosis in Agpat2−/− mice.

A team-based approach to minimally invasive esophagectomy can be used that will meet or exceed reported benchmarks.

The technique suggests an approach of managing the gastric remnant and preventing delayed gastric emptying which resulted in a decreased length of hospital stay.