Tangier disease (TD) is a human
genetic disorder associated with defective
apolipoprotein-I-induced
lipid efflux and increased atherosclerotic susceptibility. It has been linked to mutations in the
ATP-binding cassette
protein A1 (ABCA1). Here we describe the establishment of permanent Tangier cell lines using
telomerase. Ectopic expression of the catalytic subunit of human
telomerase extended the life span of control and TD skin fibroblasts, and (in contrast to immortalization procedures using viral oncogenes) did not impair
apolipoprotein A-I-induced
lipid efflux. The key characteristics of TD fibroblasts (reduced
cholesterol and
phospholipid efflux) were observed both in primary and
telomerase-immortalized fibroblasts from two unrelated homozygous patients. Surprisingly, the
apolipoprotein-inducible
cholesterol efflux in TD cells was significantly improved after immortalization (up to 40% of normal values). In contrast to ABCA1-dependent
cholesterol efflux, this efflux was not inhibited by
brefeldin A,
glybenclamide, or intracellular
ATP depletion but was inhibited in the presence of
cytochalasin D.
Apolipoprotein A-I-dependent
cholesterol efflux was inversely correlated with the population doubling number in cell culture and was inhibited up to 40% in near-senescent normal diploid fibroblasts. This inhibition was completely reversed by
telomerase. Thus ectopic expression of
telomerase is a way to circumvent the lack of critical experimental material and represents a major improvement for studying
cholesterol efflux pathways in
lipid disorders. Our findings indicate the existence of an ABCA1-independent but cytoskeleton-dependent
cholesterol removal pathway that may help to prevent early
atherosclerosis in
Tangier disease but may also be sensitive to aging phenomena ex vivo and possibly in vivo.