Lipoprotein lipase deficiency in chronic kidney disease is accompanied by down-regulation of endothelial GPIHBP1 expression

Abstract

Background: Chronic renal failure (CRF) is associated with hypertriglyceridemia and impaired clearance of very low density lipoprotein (VLDL) and chylomicrons which are largely due to lipoprotein lipase (LPL) deficiency/dysfunction. After its release from myocytes and adipocytes, LPL binds to the endothelium in the adjacent capillaries where it catalyzes hydrolysis of triglycerides in VLDL and chylomicrons. The novel endothelium-derived molecule, glycosylphosphatidylinositol-anchored binding protein 1 (GPIHBP1), plays a critical role in LPL metabolism and function by anchoring LPL to the endothelium and binding chylomicrons. GPIHBP1-deficient mice and humans exhibit severe hypertriglyceridemia and diminished heparin-releasable LPL, pointing to the critical role of GPIHBP1 in regulation of LPL activity. Given its central role in regulation of LPL activity and triglyceride metabolism, we explored the effect of chronic kidney disease (CKD) on GPIHBP1 expression.

Methods: Expression of GPIHBP1 and LPL were determined by reverse transcriptase-polymerase chain reaction, Western blot and immunohistochemical analyses in the adipose tissue, skeletal muscle and myocardium of rats 12 weeks after 5/6 nephrectomy (CRF) or sham-operation (control).

Results: Compared to the controls, the CRF group exhibited severe hypertriglyceridemia, significant reduction of the skeletal muscle, myocardium and adipose tissue LPL mRNA and protein abundance. This was accompanied by parallel reductions of GPIHBP1 mRNA abundance and immunostaining in the tested tissues.

Conclusions: LPL deficiency in CKD is associated with and compounded by GPIHBP1 deficiency. Together these abnormalities contribute to impaired clearance of triglyceride-rich lipoproteins, diminished availability of lipid fuel for energy storage in adipocytes and energy production in myocytes and consequent hypertriglyceridemia, cachexia, muscle weakness and atherosclerosis.

Fig. 1

Bar graphs depicting LPL/beta-actin mRNA ratios and GPIHBP1/beta-actin mRNA ratios in the skeletal muscle and adipose tissues of the CRF and normal control groups. N = 6 in each group, *P < 0.05, **0.01, ***0.001

Fig. 2

Representative Western blot and group data depicting LPL and beta actin protein abundance in the subcutaneous fat (a), visceral fat (b), skeletal muscle (c), and myocardium (d) of the CRF and normal control groups. N = 6 in each group, *P < 0.05, ***0.001

Fig. 3

Representative photomicrographs depicting GPIHBP1 immunostaining of the skeletal muscle, myocardium, and adipose tissue of a CRF and a normal control rat