LAL (Lysosomal Acid Lipase) Promotes Reverse Cholesterol Transport In Vitro and In Vivo

OBJECTIVE

To explore the role of LAL (lysosomal acid lipase) in macrophage cholesterol efflux and whole-body reverse cholesterol transport.

APPROACH AND RESULTS

Immortalized peritoneal macrophages from lal^-/- mice showed reduced expression of ABCA1 (ATP-binding cassette transporter A1) and ABCG1 (ATP-binding cassette transporter G1), reduced production of the regulatory oxysterol 27-hydroxycholesterol, and impaired suppression of cholesterol synthesis on exposure to acetylated low-density lipoprotein when compared with lal^+/+ macrophages. LAL-deficient mice also showed reduced hepatic ABCG5 (ATP-binding cassette transporter G5) and ABCG8 (ATP-binding cassette transporter G8) expression compared with lal^+/+ mice. LAL-deficient macrophages loaded with [³H]-cholesteryl oleate-labeled acetylated low-density lipoprotein showed impaired efflux of released [³H]-cholesterol to apoA-I (apolipoprotein A-I), with normalization of [³H]-cholesteryl ester levels and partial correction of ABCA1 expression and cholesterol efflux to apoA-I when treated with exogenous rhLAL (recombinant human LAL protein). LAL-deficient mice injected intraperitoneally with lal^-/- macrophages cholesterol loaded and labeled in the same way exhibited only 1.55±0.35% total injected [³H]-cholesterol counts appearing in the feces for 48 h (n=30), compared with 5.38±0.92% in lal^+/+ mice injected with labeled lal^+/+ macrophages (n=27), P<0.001. To mimic the therapeutic condition of delivery of supplemental LAL in vivo, injection of labeled lal^-/- macrophages into lal^+/+ mice resulted in a significant increase in reverse cholesterol transport (2.60±0.46% of ³H-cholesterol counts in feces at 48 hours [n=19]; P<0.001 when compared with injection into lal^-/- mice).

CONCLUSIONS

These results indicate a critical role for LAL in promoting both macrophage and whole-body reverse cholesterol transport and the ability of supplemental LAL to be taken up and correct reverse cholesterol transport in vivo.

Lysosomal acid lipase deficiency impairs regulation of ABCA1 gene and formation of high density lipoproteins in cholesteryl ester storage disease

ATP-binding cassette transporter A1 (ABCA1) mediates the rate-limiting step in high density lipoprotein (HDL) particle formation, and its expression is regulated primarily by oxysterol-dependent activation of liver X receptors. We previously reported that ABCA1 expression and HDL formation are impaired in the lysosomal cholesterol storage disorder Niemann-Pick disease type C1 and that plasma HDL-C is low in the majority of Niemann-Pick disease type C patients. Here, we show that ABCA1 regulation and activity are also impaired in cholesteryl ester storage disease (CESD), caused by mutations in the LIPA gene that result in less than 5% of normal lysosomal acid lipase (LAL) activity. Fibroblasts from patients with CESD showed impaired up-regulation of ABCA1 in response to low density lipoprotein (LDL) loading, reduced phospholipid and cholesterol efflux to apolipoprotein A-I, and reduced α-HDL particle formation. Treatment of normal fibroblasts with chloroquine to inhibit LAL activity reduced ABCA1 expression and activity, similar to that of CESD cells. Liver X receptor agonist treatment of CESD cells corrected ABCA1 expression but failed to correct LDL cholesteryl ester hydrolysis and cholesterol efflux to apoA-I. LDL-induced production of 27-hydroxycholesterol was reduced in CESD compared with normal fibroblasts. Treatment with conditioned medium containing LAL from normal fibroblasts or with recombinant human LAL rescued ABCA1 expression, apoA-I-mediated cholesterol efflux, HDL particle formation, and production of 27-hydroxycholesterol by CESD cells. These results provide further evidence that the rate of release of cholesterol from late endosomes/lysosomes is a critical regulator of ABCA1 expression and activity, and an explanation for the hypoalphalipoproteinemia seen in CESD patients.