MOLECULAR MECHANISMS OF RENAL DISEASE IN CARRIERS OF LCAT GENE MUTATIONS

BACKGROUND: Familial LCAT deficiency (FLD) is a rare genetic disease characterized by the complete inactivity of LCAT, the only human enzyme able to esterify cholesterol in plasma; as a consequence, carriers’ lipid and lipoprotein profile presents low HDL-C concentration, the accumulation of small and discoidal preβ-HDL particles and LpX. Renal disease is the major cause of morbidity and mortality in FLD carriers but the molecular mechanisms of kidney failure are poorly understood. Currently, there are no effective therapies available for these patients and the use of synthetic HDL is under investigation. Furthermore, a condition of acquired LCAT deficiency can characterize common pathologies, such as chronic kidney disease. AIM: Aim of this project was to analyze the unknown aspects of renal disease in LCAT deficiency, including the molecular mechanisms behind the onset of renal damage and the characterization of the lipid alterations responsible for this condition, the study of potential effective therapeutic strategies and the evaluation of the impact of non-genetic LCAT reduction on renal disease development in general population, RESULTS: The characterization of LCAT deficient carriers’ HDL by lipidomics analyses identified alterations in phospholipids and sphingolipids classes, including an accumulation of phosphatidylethanolamine, dihydroceramides and ceramides, as well as a depletion in phosphatidylethanolamine plasmalogen. Moreover, carriers’ HDL were enriched in short and saturated fatty acids and depleted in long chain polyunsaturated fatty acids. These alterations could potentially trigger some nephrotoxic mechanisms identified through the in vitro studies in podocytes and tubular cells, such as the increased oxidative stress and apoptosis induced by FLD carriers’ lipoprotein alterations. The metabolism and effect of a synthetic HDL, CER-001, was evaluated in murine model of LCAT deficiency; results collected in this part showed an amelioration of lipid profile after CER-001 treatment, with an increase of HDL-C and a reduction of triglycerides. Even more important, the molecule ameliorated renal function, reducing the albuminuria and restoring nestin and nephrin expression, by removing cholesterol accumulated in the kidney. The results set the basis to test the molecule in one FLD carrier, in which an analogous mechanism was identified by in vitro studies. The results collected in the last part of the work highlighted the predictive values of non-genetic reduction in LCAT concentration on the renal disease progression in general population. The development of renal damage could be partially explained by the pro-oxidant effect mediated by the sera from subjects with low LCAT in renal cells; the involvement of the enzyme was demonstrated through the restoration of the antioxidant propriety induced by in vitro incubation of serum with rhLCAT. CONCLUSION: Results collected within this project provided a deeper knowledge of the alterations in HDL lipid composition and the consequent nephrotoxic mechanisms in LCAT deficiency. Moreover, treatment with CER-001 demonstrated a beneficial effect on the kidney disease in LCAT deficient mice, supporting the testing of the formulation in FLD carriers. Finally, the evaluation of the relationship between low LCAT levels and progression of renal disease revealed that LCAT concentration can predict renal kidney injury in general population.