Efeito do nocaute da mitofusina 2 sobre a mitocôndria, o retículo endoplasmático e a mitofagia em oócitos murinos

Abstract

Mitofusins ​​1 (MFN1) and 2 (MFN2) are transmembrane GTPases present in the outer mitochondrial membrane and involved in the regulation of mitochondrial fusion. Since MFN2 is also present in the membrane of the endoplasmic reticulum (ER), it is also responsible for regulating the morphology and its interaction with the mitochondria. Thus, there is increasing evidence that MFN2 plays a key role in the regulation of mitochondrial function and ER, as well as the autophagic pathway. However, little is known about its role in the oocyte. Recently, we have observed that the conditional knockout of Mfn2 in murine oocytes (Mfn2-null) does not significantly alter fertility, but results in hyperglycemia in the offspring. Therefore, the objective of this work was to investigate the molecular mechanisms that result in these phenotypes. The effects of the conditional knockout of Mfn2 on the oocyte were evaluated considering the function of mitochondria, RE and the occurrence of mitofagia. For this, we first confirmed the effects of the conditional knockout of Mfn2. Knockout oocytes for Mfn2 were able to develop normally when matured in vitro. Pups from knockout oocytes showed alterations in blood glucose levels in the tests of glucose intolerance and insulin resistance when compared to wild-type oocyte (WT) pups. In addition, we found alterations in mitochondria of oocyte knockout regarding number (WT = 0.061 ± 0.004 and Mfn2-null = 0.037 ± 0.003 organelle / μm2), crests morphology, area (WT = 0.589 ± 0.015 and Mfn2-null = 1.673 ± 0.101 μm2) and contact with RE. However, Mfn2 knockout resulted in decreased lipid content in ovulated oocytes (WT = 13.07 ± 0.96 and Mfn2-null = 9.65 ± 0.64 % of lipid-occupied area of ​​ooplasm). In addition, no evidence was found at the transcriptional level of ER stress. As regards mitophagy, no knockout effect of Mfn2 was observed on the expression of genes involved in this pathway, as well as on co-localization between mitochondria and autophagosomes (WT = 0.65 ± 0.05 and Mfn2-null = 0.53 ± 0.04 AU). Thus, these findings demonstrate that conditional knockout of Mfn2 in the oocyte results in metabolic changes in offspring, most likely due to changes in morphology, function and contact between mitochondria and ER. However, the molecular mechanism by which this occurs still lacks elucidation. Furthermore, we have demonstrated that conditional knockout of Mfn2 can be a good model for the study of the inheritance of metabolic syndromes.