Residual cholesterol synthesis and simvastatin induction of cholesterol synthesis in Smith–Lemli–Opitz syndrome fibroblasts

Abstract

Smith-Lemli-Opitz syndrome (RSH/SLOS) is an autosomal recessive, malformation syndrome caused by mutations in the 3b-hydroxysterol D 7-reductase gene (DHCR7). DHCR7 catalyzes the reduction of 7-dehydrocholesterol (7DHC) to cholesterol. We report the mutation analysis and determination of residual cholesterol synthesis in 47 SLOS patients, and the effects of treatment of SLOS skin fibroblasts with simvastatin. Using deuterium labeling we have quantified the amount of synthesized cholesterol and 7DHC in homozygote, heterozygote, and control fibroblast cell lines. In SLOS fibroblasts, the fraction of synthesized cholesterol to total sterol synthesis ranged from undetectable to over 50%. This establishes that different mutant alleles encode enzymes with varying degrees of residual activity. There was a correlation between increased phenotypic severity and decreased residual cholesterol synthesis (r 2 = 0.45, p < 0.0001). Simvastatin treatment of SLOS fibroblasts with residual DHCR7 enzymatic activity decreased 7DHC levels and increased cholesterol synthesis. This increase in cholesterol synthesis is due to increased expression of a mutant allele with residual function. Determination of residual enzymatic activity for specific DHCR7 mutant alleles will help in understanding the processes underlying the broad phenotypic spectrum found in this disorder and will be useful in identifying patients who may benefit from simvastatin therapy. Published by Elsevier Inc.

Mutations in the human SC4MOL gene encoding a methyl sterol oxidase cause psoriasiform dermatitis, microcephaly, and developmental delay

“…In agreement with these findings, statins have been reported to suppress Th1-biased cytokine production in both cultured microglia and a mouse model (22). To investigate a possible association between the defect in cholesterologenesis and cytokine production, we treated control and patient fibroblasts with simvastatin, which reduces cholesterol biosynthesis intermediates including methylsterols (23,24). After 24 hours, IL-6 production by patient fibroblasts was significantly decreased even in the presence of exogenous TNF-α ( Figure 4D), suggesting that the abnormal cytokine production is likely associated with cholesterologenesis.…”

Malformation syndromes caused by disorders of cholesterol synthesis

“…If increased expression of a hypomorphic DHCR7 allele increases cholesterol synthesis, then, because it crosses the blood-brain barrier, simvastatin might be effective in increasing brain cholesterol synthesis. This hypothesis is supported by both in vitro ( 66 ) and in vivo experiments utilizing a hypomorphic mouse model ( 39 ). However, to date, a paradoxical increase in serum cholesterol levels in response to simvastatin therapy has not been confi rmed.…”

“…The most common mutation, c.964-1G>C (IVS8-1G>C), is a splice acceptor mutation that accounts for approximately onethird of all reported mutant alleles. Inappropriate splicing of the IVS8-1G>C allele leads to the insertion of 134 bp of intronic sequence into the mRNA transcript ( 62 ) and is a null allele ( 66 ). Other common (5-10% allele frequency) mutations are p.T93M, p.W151X, p.V326L, and p.R404C.…”

“…Genotype-phenotype correlations in SLOS are poor ( 67 ). Many of the missense mutations result in residual enzymatic activity, and, in general, residual DHCR7 activity is associated with less severe SLOS phenotypes ( 66 ). However, factors other than genotype and residual activity appear to signifi cantly infl uence subject phenotype ( 67 ).…”

The novel p53 target TNFAIP8 variant 2 is increased in cancer and offsets p53-dependent tumor suppression

“…49 DOX, staurosporine, and nutlin-3 (Sigma-Aldrich, St. Louis, MO, USA) were used at 0.3 μg/ml, 2.5 μM, or 10 μM, respectively. Lentiviral transduction and plasmid transfection.…”