Identification of a gene variant in the master regulator of lipid metabolism SREBP-1 in a family with a novel form of severe combined hypolipidemia.
Atherosclerosis 2011;
218:134-43. [PMID:
21645898 DOI:
10.1016/j.atherosclerosis.2011.05.008]
[Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Revised: 05/05/2011] [Accepted: 05/09/2011] [Indexed: 12/01/2022]
Abstract
OBJECTIVE
Alterations of lipid metabolism play a pivotal role in the development of atherosclerosis and its complications, today's major mortality risks. The predominant regulators controlling cholesterol- and fatty acids synthesis in liver are the sterol regulatory element-binding proteins (SREBPs), a family of transcription factors that were formerly identified as cholesterol sensor for LDLR gene expression. Variation of gene structure in these genes might therefore indicate a predisposition to develop complications like myocardial infarction and stroke.
METHODS
We investigated 190 unrelated German subjects, including 69 subjects with LDL-cholesterol <55mg/dl, for mutations in SREBP genes SREBF-1 and SREBF-2 by direct sequencing. The impact on SREBP functionality was analyzed by protein biochemical analyses, promoter reporter gene assays and gene expression studies.
RESULTS
A missense mutation in SREBF-1 (c.332 C>T; P111L) was identified in a subject with LDL-cholesterol <5mg/dl. Examination of the subject's family confirmed the mutation in two of three siblings. Detailed clinical evaluation of these subjects disclose a novel form of primary combined hypolipidemia only in SREBP-1a P111L carriers, characterized by low levels of apoB and apoA1, low triglyceride, LDL-cholesterol and HDL-cholesterol levels. Functional analyses indicated that the mutation abolishes phosphorylation of SREBP-1. As a consequence transcriptional activation of classical target genes, i.e. LDLR, HMG-CoAR, FAS, ABCA1, but also MTTP, was dramatically reduced.
CONCLUSIONS
Phosphorylation of SREBP-1, the master regulator of genes for central rate limiting enzymes of cholesterol and lipid metabolism, appears to be a biological principle with clinical implications.
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