The HO-1/CO System and Mitochondrial Quality Control in Skeletal Muscle

Repeated hyperbaric oxygen exposure accelerates fatigue and impairs SR-calcium release in mice

Breathing hyperoxic gas is common in diving and accelerates fatigue after prolonged and repeated exposure. The mechanism(s) remain unknown but may be related to increased oxidants that interfere with skeletal muscle calcium trafficking or impaired aerobic ATP production. To determine these possibilities, C57BL/6J mice were exposed to hyperbaric oxygen (HBO2) for 4 h on three consecutive days or remained in room air. Postfinal exposure, fatigue was determined by grip strength and run-to-exhaustion tests. Other measurements included indices of oxidant stress and antioxidant defenses, mitochondrial bioenergetics, caffeine-induced sarcoplasmic reticulum-calcium release, and S-nitrosylation of ryanodine receptor 1 (RyR1). Despite grip strength being unaffected by repeated HBO2 exposure, mean running time was reduced by 50%. In skeletal muscle from HBO2 exposed mice, superoxide production was significantly increased, resulting in elevated lipid and DNA (nuclear and mitochondrial) oxidation. Accompanying increased oxidant stress was a reduction in glutathione content and increased Sod1 and Hmox1 gene expression; Ucp3 mRNA was reduced. Mitochondrial respiration, mitochondrial membrane potential, and NAD+/NADH were not influenced by HBO2. In contrast, caffeine-induced sarcoplasmic reticulum (SR)-calcium release was reduced by 66% and S-nitrosylation of RyR1 was increased by 45%. Exposing mice to repeated HBO2 increases oxidant stress that activates some antioxidant defenses. Mitochondrial function is not altered and could be related to decreased production of UCP3 that serves to maintain the electrochemical proton gradient. S-nitrosylation of RyR1 may promote SR-calcium leak and reduce content, a potential mechanism for repeated HBO2-induced fatigue.NEW & NOTEWORTHY Breathing hyperoxic gas during prolonged and repeated dives causes fatigue but the mechanisms are unknown. Here, we show in mice exposed to repeated hyperbaric oxygen that running fatigue is accelerated and accompanied by increased skeletal muscle oxidant stress and reduced caffeine-induced sarcoplasmic reticulum (SR)-calcium release. The latter may be due to increased S-nitrosylation of ryanodine receptor 1 (RyR1) and be a mechanism for impaired physical performance after repeated oxygen diving.

Carbon monoxide-loaded cell therapy as an exercise mimetic for sarcopenia treatment

Sarcopenia is characterized by loss of muscle strength and muscle mass with aging. The growing number of sarcopenia patients as a result of the aging population has no viable treatment. Exercise maintains muscle strength and mass by increasing peroxisome growth factor activating receptor γ-conjugating factor-1α (PGC-1α) and Akt signaling in skeletal muscle. The present study focused on the carbon monoxide (CO), endogenous activator of PGC-1α and Akt, and investigated the therapeutic potential of CO-loaded red blood cells (CO-RBCs), which is bioinspired from in vivo CO delivery system, as an exercise mimetic for the treatment of sarcopenia. Treatment of C2C12 myoblasts with the CO-donor increased the protein levels of PGC-1α which enhanced mitochondrial biogenesis and energy production. The CO-donor treatment also activated Akt, indicating that CO promotes muscle synthesis. CO levels were significantly elevated in the skeletal muscle of normal mice after intravenous administration of CO-RBCs. Furthermore, CO-RBCs restored the mRNA expression levels of PGC-1α in the skeletal muscle of two experimental sarcopenia mouse models, denervated (Den) and hindlimb unloading (HU) models. CO-RBCs also restored muscle mass in Den mice by activating Akt signaling and suppressing the muscle atrophy factors myostatin and atrogin-1, and oxidative stress. Treadmill tests further showed that the reduced running distance in HU mice was significantly restored by CO-RBC administration. These findings suggest that CO-RBCs have potential as an exercise mimetic for sarcopenia treatment.

Heme oxygenase-1: The roles of both good and evil in neurodegenerative diseases

Heme oxygenase-1 (HO-1) is the only way for cells to decompose heme. It can cleave heme to produce carbon monoxide (CO), ferrous iron (Fe2+ ), and biliverdin (BV). BV is reduced to bilirubin (BR) by biliverdin reductase(BVR). In previous studies, HO-1 was considered to have protective effects because of its anti-inflammatory, anti-apoptosis, and antiproliferation functions. However, emerging experimental studies have found that the metabolites derived from HO-1 can cause increase iin intracellular oxidative stress, mitochondrial damage, iron death, and autophagy. Because of its particularity, it is very meaningful to understand its exact mechanism. In this review, we summarized the protective and toxic effects of HO-1, its potential mechanism, its role in neurodegenerative diseases and related drug research. This knowledge may be beneficial to the development of new therapies for neurodegenerative diseases and is crucial to the development of new therapeutic strategies and biomarkers.