Effect of Hypoxia on Lipid Accumulation in Cultured Fibroblasts from Normal Rabbit and Watanabe Heritable Hyperlipidemic Rabbit

We studied the effect of hypoxia on lipid accumulation in cultured fibroblasts from normal rabbits (normal fibroblasts) and in low density lipoprotein (LDL) receptor-negative fibroblasts from WHHL (Watanabe heritable hyperlipidemic) rabbits (WHHL fibroblasts). These cells were incubated in medium with normolipemic rabbit serum (NRS) or hyperlipemic rabbit serum (HRS). The cells were incubated in a humidified atmosphere of either 20% O2, 75% N2, and 5% CO2 (control cells) or 2% O2, 93% N2, and 5% CO2 (hypoxic cells).After 48h incubation of normal fibroblasts in medium with 20% NRS, free fatty acid (FFA) levels were increased slightly and the triglyceride (TG) level markedly in hypoxic cells. In the medium with 20% HRS, in addition to the increased FFA and TG levels, the free cholesterol level was increased slightly and the esterified cholesterol level markedly in hypoxic cells. Moreover, in WHHL fibroblasts, which lack LDL receptors, cellular lipid accumulation was also observed after 48h incubation in the medium with 20% HRS, and hypoxic incubation enhanced the cellular cholesterol and TG accumulation, as in normal fibroblasts.These results suggest that under hyperlipemic conditions, non LDL receptor-mediated uptake of lipoproteins plays a major role in cellular lipid deposition and that tissue hypoxia promotes lipid accumulation in peripheral cells by the LDL receptor-independent mechanisms.