Analysis of BNIP3 and BNIP3L/Nix expression in cybrid cell lines harboring two LHON-associated mutations.

Abstract

Mitochondria are key players in cell death through the activation of the intrinsic apoptosis pathway. BNIP3 and BNIP3L/Nix are outer mitochondrial membrane bifunctional proteins which because of containing both BH3 and LIR domains play a role in cellular response to stress by regulation of apoptosis and selective autophagy. Leber’s Hereditary Optic Neuropathy (LHON) is the most common mitochondrial disease in adults, characterized by painless loss of vision caused by atrophy of the optic nerve. The disease in over 90% of cases is caused by one of three mutations in the mitochondrial genome: 11778G>A, 3460G>A or 14484T>C. The pathogenic processes leading to optic nerve degeneration are largely unknown, however, the most common explanation is that mtDNA mutations increase the apoptosis level in this tissue. Here we present the results of analysis of BNIP3 and BNIP3L/Nix proteins in cells harboring a combination of the 11778G>A and the 3460G>A LHON mutations. Experiments performed on cybrids revealed that BNIP3 protein level is decreased in LHON cells compared to controls. CCCP treatment resulted in apoptosis induction only in control cells. Moreover, we also noticed reduced level of autophagy in LHON cybrids. The presented results suggest that in cells carrying LHON mutations expression of proteins involved in regulation of apoptosis and autophagy is decreased what in turn may disturb cell death pathways in those cells and affect cellular response to stress.

Mitophagy: An Emerging Target in Ocular Pathology

“…The reduced mitophagy phenotype in LHON is supported by Sharma et al, 175 who demonstrated that activation of mitophagy in cells harboring LHON mtDNA mutations rescues mitochondrial function and cell survival. Work by Jankauskaitė et al (2020) 172 and Kodroń et al (2019) 176 also showed higher mitochondrial mass, lower mitophagic receptor BNIP3, and lower autophagic flux present in LHON lymphoblast cultures treated with testosterone, as well as in cybrid LHON mutation cultures, supporting a reduced mitophagy phenotype in LHON. 172,176 Genome-wide linkage studies have further shown two PARL SNPs associated with LHON mitochondrial disease.…”

“…Work by Jankauskaitė et al (2020) 172 and Kodroń et al (2019) 176 also showed higher mitochondrial mass, lower mitophagic receptor BNIP3, and lower autophagic flux present in LHON lymphoblast cultures treated with testosterone, as well as in cybrid LHON mutation cultures, supporting a reduced mitophagy phenotype in LHON. 172,176 Genome-wide linkage studies have further shown two PARL SNPs associated with LHON mitochondrial disease. 177 PARL protease is responsible for processing the antiapoptotic form of OPA1, which subsequently prevents the release of mitochondrial cytochrome c into the cytosol, normally an intrinsic signal initiating apoptosis.…”

BNIP3L/NIX-mediated mitophagy: molecular mechanisms and implications for human disease

“…It is unraveled that whether upregulated BNIP3L can increase mitophagy activity, although some papers denoted that mitophagy defects might underlie ALS pathology [ 128 , 129 ]. Besides PD and ALS, other studies indicated the potential involvement of BNIP3L-mediated autophagy/mitophagy in other neurodegenerative conditions, but the evidence is not conclusive [ 47 , 130 , 131 ]. Finally, there is no evidence indicating an association between Bnip3l mutation and neurodegeneration, although an emerging preliminary study implied its involvement in schizophrenia [ 132 ].…”

The Role of Mitophagy in Hereditary Optic Neuropathies. Literature Review

“…В еще одной работе было обнаружено, что цибриды с высоким уровнем гетероплазмии (более 80 %) по «первичным» мутациям m.3460G>A и m.11778G>A формировали меньше аутофагосом в галактозной среде, чем цибриды дикого типа. Эти же цибриды синтезировали меньше рецепторов аутофагии -NIX, что может говорить о нарушениях процессов аутофагии [45]. Важное наблюдение было сделано в работе на цибридах, полученных из клеток, содержащих как нормальные, так и митохондрии с мутацией m.11778G>A. Индукция митофагии рапамицином вызывала избирательное уничтожение митохондрий в цибридах.…”