Testosterone increases apoptotic cell death and decreases mitophagy in Leber’s hereditary optic neuropathy cells

Abstract

Leber's hereditary optic neuropathy (LHON) is one of the most common mitochondrial diseases caused by point mutations in mitochondrial DNA (mtDNA). The majority of diagnosed LHON cases are caused by a point mutation at position 11,778 in the mitochondrial genome. LHON mainly affects young men in their 20s and 30s with usually poor visual prognosis. It remains unexplained why men are more likely to develop the disease and why only retinal ganglion cells are affected. In this study, a cell model was used for the first time to investigate the influence of testosterone on the cell death mechanism apoptosis and on an autophagy/mitophagy. Cells with m.11778G > A were found to be significantly more susceptible to nucleosome formation and effector caspase activation that serve as hallmarks of apoptotic cell death. Cells having this mutation expressed higher levels of mitophagic receptors BNIP3 and BNIP3L/Nix in a medium with testosterone. Moreover, cells having the mutation exhibited greater mitochondrial mass, which suggests these cells have a decreased cell survival. The observed decrease in cell survival was supported by the observed increase in apoptotic cell death. Autophagy was analyzed after inhibition with Bafilomycin A1 (Baf A1). The results indicate impairment in autophagy in LHON cells due to lower autophagic flux supported by observed lower levels of autophagosome marker LC3-II. The observed impaired lower autophagic flux in mutant cells correlated with increased levels of BNIP3 and BNIP3L/Nix in mutant cells.

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.…”

“…LHON is characterized by RGC degeneration and subsequent loss of central vision, predominately in young men. 172 Dombi et al 173 showed that mtDNA mutation m.13051G>A is associated with increased mitophagy (assessed by LC3 and TOM20 colocalization in addition to mtDNA quantification) in patient-derived fibroblasts with LHON/Leigh phenotypes. The use of idebenone, a synthetic antioxidant similar to coenzyme Q10, reduced mitophagy in the fibroblast cultures and is thought to provide a possible therapeutic effect.…”

Effects of Age and Lifelong Moderate-Intensity Exercise Training on Rats’ Testicular Function

“…This is in part consistent with other studies that reported mitochondria-mediated ROS overload after high-intensity continuous running [ 50 ]. Testosterone seems to have important mitoprotective and antimitophagy functions in many tissues [ 51 , 52 , 53 , 54 ], alleviating mitochondrial ROS accumulation [ 55 ] and inducing the expression of Nrf1 [ 53 ], which was not observed in this study. Despite quite contradictory, these results may suggest a possible mechanism of protection in testis in which aging and physical exercise impair mitochondrial activity leading to an increased production of ROS with a consequent activation of the antioxidant defense system to prevent severe testicular damage.…”

Developments in the Treatment of Leber Hereditary Optic Neuropathy

“…It is hypothesised that external metabolic stressors interfere with normal mitochondrial homeostasis by upsetting the balance between mitochondrial biogenesis and mitophagy [ 7 ]. Sex hormones have also been implicated, in particular the protective effects of oestrogens from oxidative stress and the role of testosterone in increasing RGC apoptosis and reduced mitophagy [ 8 , 9 ].…”