Enhanced resistance to Ca2+-induced mitochondrial permeability transition in the long-lived red-footed tortoise Chelonoidis carbonaria

The effects of oxidative stress and intracellular calcium on mitochondrial permeability transition pore formation in equine spermatozoa

The in vitro storage of stallion spermatozoa for use in artificial insemination leads to oxidative stress and imbalances in calcium homeostasis that trigger the formation of the mitochondrial permeability transition pore (mPTP), resulting in premature cell death. However, little is understood about the dynamics and the role of mPTP formation in mammalian spermatozoa. Here, we identify an important role for mPTP in stallion sperm Ca2+ homeostasis. We show that stallion spermatozoa do not exhibit "classical" features of mPTP; specifically, they are resistant to cyclosporin A-mediated inhibition of mPTP formation, and they do not require exogenous Ca2+ to form the mPTP. However, chelation of endogenous Ca2+ prevented mPTP formation, indicating a role for intracellular Ca2+ in this process. Furthermore, our findings suggest that this cell type can mobilize intracellular Ca2+ stores to form the mPTP in response to low Ca2+ environments and that under oxidative stress conditions, mPTP formation preceded a measurable increase in intracellular Ca2+, and vice versa. Contrary to previous work that identified mitochondrial membrane potential (MMP) as a proxy for mPTP formation, here we show that a loss of MMP can occur independently of mPTP formation, and thus MMP is not an appropriate proxy for the detection of mPTP formation. In conclusion, the mPTP plays a crucial role in maintaining Ca2+ and reactive oxygen species homeostasis in stallion spermatozoa, serving as an important regulatory mechanism for normal sperm function, thereby contraindicating the in vitro pharmacological inhibition of mPTP formation to enhance sperm longevity.

Aggravation of hepatic lipidosis in red-footed tortoise Chelonoidis carbonaria with age is associated with alterations in liver mitochondria

The occurrence of hepatic lipidosis is commonly reported in different reptilian species, especially in animals under captivity. Liver accumulation of fat is associated with disorders, better described in mammals as non-alcoholic fatty liver diseases (NAFLD), ranging from simple steatosis, to non-alcoholic steatohepatitis (NASH), and to more severe lesions of cirrhosis and hepatocellular carcinoma. Mitochondria play a central role in NAFLD pathogenesis, therefore in this study we characterized livers of ad libitum fed captive red-footed tortoise Chelonoidis carbonaria through histological and mitochondrial function evaluations of juvenile and adult individuals. Livers from adult tortoises exhibited higher levels of lipids, melanomacrophages centers and melanin than juveniles. The observed high score levels of histopathological alterations in adult tortoises, such as microvesicular steatosis, inflammation and fibrosis, indicated the progression to a NASH condition. Mitochondrial oxygen consumption at different respiratory states and with different substrates was 30 to 58% lower in adult when compared to juvenile tortoises. Despite citrate synthase activity was also lower in adults, cardiolipin content was similar to juveniles, indicating that mitochondrial mass was unaffected by age. Mitochondrial Ca²⁺ retention capacity was reduced by 70% in adult tortoises. Overall, we found that aggravation of NAFLD in ad libitum fed captive tortoises is associated with compromised mitochondrial function, indicating a critical role of the organelle in liver disease progression in reptiles.