Alterações na homeostase redox e do retículo endoplasmático: mecanismos associados à lipodistrofia generalizada congênita do tipo 2

Abstract

Congenital generalized lipodystrophy (CGL) type 2 consists of a rare autosomal recessive syndrome characterized by almost complete lack of body fat at birth. CGL, genetically caused by loss-of-function mutations in the two alleles of the BSCL2 gene, was phenotypically characterized by hypertriglyceridemia, hyperglycemia, decreased HDL-c, and hypoadiponectinemia. These laboratory findings are important triggers for changes in redox and endoplasmic reticulum (ER) homeostasis. Therefore, our aim was to investigate if these intracellular mechanisms are part of this syndrome. Therefore, we collected the whole blood from people living in Northeastern Brazil with 0, 1 and 2 mutant alleles for the c.325dupA mutation (rs786205071) in the BSCL2 gene. Through the qPCR technique, we evaluated the expression of genes responsible for triggering the antioxidant response, DNA repair and ER stress in leukocytes. Colorimetric tests were applied to quantify lipid peroxidation products and to evaluate the redox status of glutathione, as well as to access plasma energy metabolism panorama. Conventional PCR was also chosen to observe leukocyte mitochondrial DNA lesions. We also chose the immunoblot technique for the study of gene expression of chaperone proteins related to ER stress in leukocytes, as well as plasma adiponectin concentrations. Comparing to the healthy group, subjects with the rs786205071 mutation in the 2 alleles showed increased transcription of NFE2L2, APEX1, OGG1 and αOGG1 in leukocytes, as well as the concentrations of malondialdehyde and the GSSG:GSH ratio in plasma. In addition, we also observed decreased in vitro polymerization rate of mitochondrial DNA and increased XBP1 splicing in leukocytes. In silico analyses indicated a high probability of seipin rs786205071 belonging to the ER membrane, although the aforementioned mutation removes amyloidogenic regions from that protein. In addition, we observed a decrease in the transcription of BSCL2 in these leukocytes, associated with the absence of differences in the expression pattern of HSPA5 and P4HB chaperones. In parallel, these cells showed decreased DDIT3 transcripts, but without differences in the procaspase-3 cleavage pattern. Finally, we also observed a soft increase of plasmatic triacylglycerol, together with a decrease in plasma concentrations of adiponectin and HDL-c. Together, results pointed to the presence of lipid lesions due to changes in redox homeostasis, associated with increased numbers of mitochondrial DNA damage and transcriptional recruitment of genes that participate of the antioxidant response and DNA repair. Although there is also evidence of ER stress, the rs786205071 mutation was shown to possibly have a low probability to directly generate this mechanism. In addition, the data suggest that there was no evidence of increased cell death and that decreases in adiponectin and HDL-c concentrations may act as potential triggers for changes in redox and ER homeostasis in CGL type 2.