Alterations in membrane caveolae and BKCa channel activity in skin fibroblasts in Smith–Lemli–Opitz syndrome

Abstract

The Smith-Lemli-Opitz syndrome (SLOS) is an inherited disorder of cholesterol synthesis caused by mutations in DHCR7 which encodes the final enzyme in the cholesterol synthesis pathway. The immediate precursor to cholesterol synthesis, 7-dehydrocholesterol (7-DHC) accumulates in the plasma and cells of SLOS patients which has led to the idea that the accumulation of abnormal sterols and/or reduction in cholesterol underlies the phenotypic abnormalities of SLOS. We tested the hypothesis that 7-DHC accumulates in membrane caveolae where it disturbs caveolar bilayer structure-function. Membrane caveolae from skin fibroblasts obtained from SLOS patients were isolated and found to accumulate 7-DHC. In caveolar-like model membranes containing 7-DHC, subtle, but complex alterations in intermolecular packing, lipid order and membrane width were observed. In addition, the BKCa K+ channel, which co-migrates with caveolin-1 in a membrane fraction enriched with cholesterol, was impaired in SLOS cells as reflected by reduced single channel conductance and a 50 mV rightward shift in the channel activation voltage. In addition, a marked decrease in BKCa protein but not mRNA expression levels were seen suggesting post-translational alterations. Accompanying these changes was a reduction in caveolin-1 protein and mRNA levels, but membrane caveolar structure was not altered. These results are consistent with the hypothesis that 7-DHC accumulation in the caveolar membrane results in defective caveolar signaling. However, additional cellular alterations beyond mere changes associated with abnormal sterols in the membrane likely contribute to the pathogenesis of SLOS.

7DHC-induced changes of Kv1.3 operation contributes to modified T cell function in Smith-Lemli-Opitz syndrome

“…The single-channel conductance of the BK Ca channel, which colocalizes with caveolin in CHOLrich membrane domains, is reduced and the voltage dependence of the open probability is right-shifted in SLOS fibroblasts [48]. The function of Na + /K + ATPase is also decreased in SLOS fibroblast [48].…”

“…Moreover, accumulation of the 7DHC in the plasma membrane can affect the physicalchemical behavior of the lipid bilayer, and also influence the function of membrane proteins by disrupting/modifying the raft structure and/or interacting directly with the proteins themselves [11,30,61]. The single-channel conductance of the BK Ca channel, which colocalizes with caveolin in CHOLrich membrane domains, is reduced and the voltage dependence of the open probability is right-shifted in SLOS fibroblasts [48]. The function of Na + /K + ATPase is also decreased in SLOS fibroblast [48].…”

Mutational Spectrum of Smith-Lemli-Opitz Syndrome Patients in Hungary

“…Cholesterol is an important component of the lipid rafts of cell membranes, it is the constituent of myelin, the precursor molecule of bile acids, steroid hormones and neurosteroids and plays an important role in the embryogenesis/morphogenesis as well [Kelley et al, 1996]. In SLO syndrome 7-DHC replaces cholesterol to a great extent in the steroland caveolin-rich membrane regions and disturbs cell signaling [Ren et al, 2011]. Very recently, it has been suggested that the neurological symptoms in SLO syndrome are associated with the oxysterols that are produced out of 7-DHC [Korade et al, 2010].…”

Clinical Syndromes and Associations with Persistent Pulmonary Hypertension of the Newborn

“…Disruptions in cholesterol metabolism can interrupt key signaling pathways that participate in the normal maintenance of pulmonary www.intechopen.com vascular tone. Others and we have found that caveolae-dependent signaling may be involved in this process since our patient had altered expression of caveolin-1 suggesting that additional cellular alterations beyond mere changes associated with abnormal sterols in the membrane likely contribute to the pathogenesis of SLOS (Katheria, et al, 2010;Ren et al, 2011).…”