a b s t r a c tProprotein convertase subtilisin/kexin type 9 (PCSK9), a liver-secreted plasma enzyme, restricts hepatic uptake of low-density lipoprotein (LDL) cholesterol by promoting the degradation of LDL receptors (LDLR). PCSK9 and LDLR are also expressed in insulin-producing pancreatic islet b cells, possibly affecting the function of these cells. Here we show that, compared to control mice, PCSK9-null male mice over 4 months of age carried more LDLR and less insulin in their pancreas; they were hypoinsulinemic, hyperglycemic and glucose-intolerant; their islets exhibited signs of malformation, apoptosis and inflammation. Collectively, these observations suggest that PCSK9 may be necessary for the normal function of pancreatic islets.

Summary Proprotein convertases mediate the production of a variety of peptidic mitogens by limited proteolysis of their precursors. These proteases may also participate in the autocrine production of such mitogens by cancer cells and thus contribute to the unchecked proliferation of these cells. As a step towards defining this contribution, we have examined the levels of four convertase mRNAs in human lung neoplasms using semiquantitative Northern blot analysis. Furin mRNA was expressed in all the tumours; its level in squamous cell carcinomas and adenocarcinomas was on average about threefold higher than in small-cell lung carcinomas (SCLCs). PACE4 transcripts were detected in eight of 14 adenocarcinomas and in seven of 17 squamous cell carcinomas; they were detectable in only two of seven SCLCs. PC1 mRNA was undetected in squamous cell carcinomas and in all but two adenocarcinomas; it was present in four of six SCLCs. PC2 mRNA was found in two adenocarcinomas, in one squamous cell carcinoma and in five of seven SCLCs. This preliminary survey indicates that SCLCs often carry more mRNA for the endocrine convertases PC1 and PC2 and less mRNA for the more ubiquitous furin and PACE4, suggesting inverse roles of these convertases in the development of this neoplasm.

HighlightsQuercetin-3-glucoside can increase LDLR expression by hepatocytes.Quercetin-3-glucoside can reduce PCSK9 secretion by hepatocytes.Quercetin-3-glucoside can down regulate sortilin expression.Quercetin-3-glucoside can increase LDL uptake by hepatocytes.Quercetin-3-glucoside is a potential anti-cholesterolemic agent.

ObjectivesVariants of the secreted glycoprotein, proprotein convertase subtilisin/kexin 9 (PCSK9), associate with both hypo- and hyper-cholesterolemic phenotypes. Herein, we carried out full exonic sequencing of PCSK9 documenting the frequency of single and multiple PCSK9 variations and their effects on serum lipoprotein and PCSK9 levels in Caucasian Canadians.MethodsThe 12 exons of PCSK9 were sequenced in 207 unrelated Caucasian Canadians. Minor allele frequencies of PCSK9 variants were compared amongst LDL cholesterol (LDLC) quintiles. Serum PCSK9 levels were measured by ELISA and lipoproteins by enzymatic methods. Comparisons were made with a Caucasian family cohort (n = 51) and first generation African Canadians (n = 31).ResultsIn Caucasians, but not African Canadians, the c.61_63insCTG (denoted L10Ins) and A53V PCSK9 variations were linked and their frequency was significantly higher among Caucasian Canadians with LDLC levels in the <25th percentile. In both the unrelated and family Caucasian cohorts those carrying the L10A53V PCSK9 variant had significantly lower LDLC without reduction in plasma PCSK9. The I474V PCSK9 variant associated with significantly lower serum PCSK9 and LDLC. A novel PCSK9 variant was identified; E206K. We found that the frequency of multiple PCSK9 variations was higher in first generation African Canadians.ConclusionsWe showed that the L10A53V and I474V PCSK9 variants were significantly associated with lower LDLC levels in Caucasian Canadians but differed in their effect on serum PCSK9 concentrations, illuminating differences in their mechanism of inaction and indicating that that PCSK9 measurement alone may not always be a good indicator of PCSK9 function.Full exonic sequencing of PCSK9 pointed to factors that may contribute to L10Ins PCSK9 variant loss of function in Canadians of Caucasian but not those of African descent. These included; (1) its tight linkage with the A53V variant in Caucasians and/or (2) for both the L10 and I474V, the combined (and negating) effect of multiple, differing phenotypic PCSK9 variants within individuals of African ancestry for which combinations of PCSK9 variations and their overall frequency was higher. No population studies, to our knowledge, have addressed or accessed the effect of multiple PCSK9 variants on cholesterol profiles. Our results indicate that this should be considered.

In mice, dietary Q3G could counter HCD-induced hyperlipidemia and hyperinsulinemia, in part by oppositely modulating hepatic and pancreatic PCSK9 secretion.

Proprotein convertase 1 (PC1) is a neuroendocrine proteinase involved in the proteolytic activation of precursors to hormones and neuropeptides. To determine the physiological importance of PC1, we produced a mutant mouse from embryonic stem cells in which its locus (Pcsk1) had been inactivated by homologous recombination. The inactivating mutation consisted of a 32.7-kb internal deletion and a 1.8 kb insertion of the bacterial neomycin resistance gene (neo) under the mouse phosphoglycerate kinase 1 protein (PGKneo). Intercross of Pcsk1(+/-) mice produced no Pcsk1(-/-) offspring or blastocysts; in addition, more than 80% of the offspring were Pcsk1(+/-). These observations suggested that the mutation caused preimplantation lethality of homozygous embryos and preferential transmission of the mutant allele. Interestingly, RT-PCR analysis on RNA from endocrine tissues from Pcsk1(+/-) mice revealed the presence of aberrant transcripts specifying the N-terminal half of the PC1 propeptide fused to neo gene product. Mass spectrometric profiles of proopiomelanocortin-derived peptides in the anterior pituitary were similar between Pcsk1(+/-) and Pcsk1(+/+) mice, but significantly different between male and female mice of the same genotype. Relative to their wild-type counterparts, female mutant mice exhibited stunted growth under a low fat diet, and catch-up growth under a high-fat diet. The complex phenotype exhibited by this Pcsk1 mutant mouse model may be due to PC1 deficiency aggravated by expression of aberrant gene products from the mutant allele.

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Lower LDL-C and impaired GSIS are two major phenotypes in aged PCSK9-deficient C57BL/6 mice. These phenotypes are modulated by gender and diet.