Down-regulation of tissue lipoprotein lipase expression in experimental chronic renal failure

Chronic renal failure (CRF) is associated with hypertriglyceridemia, impaired clearance of very low density lipoproteins (VLDL) and chylomicrons and their remnants as well as triglyceride-enrichment of various lipoproteins. These abnormalities are indicative of depressed lipoprotein lipase (LPL)-mediated hydrolysis of triglycerides in VLD and chylomicrons. In fact, impaired post-heparin lipolytic activity and decreased adipose tissue LPL activity has been previously demonstrated in CRF. The reduction in LPL activity in CRF has been attributed to PTH-induced insulin resistance and the presence of excess lipase inhibitors in uremic plasma. However, the effect of CRF on gene expression of LPL has not been elucidated and was studied here. Heparin-releasable, detergent-extractable and total LPL activities, as well as LPL mRNA of the heart, soleus muscle and fat body were determined in male Sprague-Dawley rats at baseline and on weeks 1, 3 and 6 following 5/6 nephrectomy (CRF group) or sham operation (control group). The CRF group exhibited a marked and steady rise in plasma triglycerides along with a steady decline in LPL activities and mRNA levels of all tissues studied. In contrast, the study parameters remained virtually unchanged throughout the study period in the control group. A strong inverse correlation was found between plasma triglycerides and LPL activity in the study animals. LPL activity was directly related to LPL mRNA. We conclude that CRF results in marked down-regulation of LPL expression that can contribute to dyslipidemia and altered energy metabolism in uremia. The effect of depressed LPL expression is compounded by the previously demonstrated elevations in uremic plasma of Apo C-III and pre-beta-HDL, which are potent inhibitors of LPL.