7-Dehydrocholesterol Modifies the Operation of Kv1.3 Channels in T Cells Isolated from Smith-Lemli-Opitz Syndrome Patients

Abstract

In vitro manipulation of membrane sterol level has an impact on the regulation of ion channels, however, a comprehensive study is lacking to confirm the physiological or pathophysiological significance of these experiment. Smith-Lemli-Opitz syndrome (SLOS) is characterized by a reduced or abolished activity of 7-dehydrocholesterol (7DHC) reductase, which leads to the elevation of the 7DHC in the tissues and blood. We utilized T cells isolated from SLOS patients to address the question if in vivo altered membrane sterol composition impairs the operation of Kv1.3, the predominant voltage-gated ion channel of T cells, and if altered Kv1.3 function is reflected in impaired mitogenic responses of SLOS T lymphocytes.Using whole-cell patch-clamp technique we showed that the activation kinetics of Kv1.3 is slower and the midpoint of the voltage-dependence of steady-state activation is shifted to depolarized potentials in SLOS T cells as compared to age-matched controls. Similar changes in the kinetic and equilibrium parameters of Kv1.3 gating were detected in control T cells loaded with 7DHC using 7DHC/cyclodextrin complex. Upon removal of putative sterol binding sites of Kv1.3 the channel become insensitive to 7DHC loading. Functional assays revealed that modified operation of Kv1.3 in the SLOS T cells is associated with impaired proliferation rate (CFSE method) and a defect in the early steps of Kv1.3¬- and Ca2+-dependent activation process (CD154/CD40L expression) in CD3+ cells.Our conclusion is that the function of Kv1.3 is modified in SLOS via a direct coupling to the 7DHC in the cell membrane. We propose that this ion channel-sterol interaction reveals a molecular mechanism that may contribute to the pathophysiological conditions in SLOS and lead to the most prominent neurological and cardiovascular symptoms via influencing the physiological function of ion channels.