Acute Hypobaric Hypoxia-Mediated Biochemical/Metabolic Shuffling and Differential Modulation of S1PR-SphK in Cardiac and Skeletal Muscles

Expression of protein phosphatase 4 in different tissues under hypoxia

Relevant research data shows that there is a certain degree of energy metabolism imbalance in highland residents. Protein phosphatase 4 (PP4) has been found as a new factor in the regulation of sugar and lipid metabolism. Here, we investigate the differential expression of PP4 at a simulated altitude of 4,500 m in the heart, lung, and brain tissues of rats. A hypoxic plateau rat model was established using an animal decompression chamber. A blood routine test was performed by an animal blood cell analyzer on rats cultured for different hypoxia periods at 4,500 m above sea level. Quantitative polymerase chain reaction (qPCR) and western blot were used to detect the changes of protein phosphatase 4 catalytic subunit (PP4C) gene and protein in heart, lung, and brain tissues. The PP4C gene with the highest expression level found in rats slowly entering the high altitude area (20 m-2200 m-7 d-4500 m-3 d) was about twice as high as the low elevation group (20 m above sea level). The simulated high-altitude hypoxia induced an increase of PP4C expression level in all tissues, and the expression in the lung tissue was twice as expressed as heart and brain tissue at high altitude (P < 0.05). These results suggest that the PP4 phosphatase complex is ubiquitously expressed in rat tissues and likely involved in adaptation to or disease associated with high-altitude hypoxia.

Effect of hypobaric hypoxia on the fiber type transition of skeletal muscle: a synergistic therapy of exercise preconditioning with a nanocurcumin formulation

Hypobaric hypoxia (HH) leads to various adverse effects on skeletal muscles, including atrophy and reduced oxidative work capacity. However, the effects of HH on muscle fatigue resistance and myofiber remodeling are largely unexplored. Therefore, the present study aimed to explore the impact of HH on slow-oxidative fibers and to evaluate the ameliorative potential of exercise preconditioning and nanocurcumin formulation on muscle anti-fatigue ability. C2C12 cells (murine myoblasts) were used to assess the effect of hypoxia (0.5%, 24 h) with and without the nanocurcumin formulation (NCF) on myofiber phenotypic conversion. To further validate this hypothesis, male Sprague Dawley rats were exposed to a simulated HH (7620 m) for 7 days, along with NCF administration and/or exercise training. Both in vitro and in vivo studies revealed a significant reduction in slow-oxidative fibers (p < 0.01, 61% vs. normoxia control) under hypoxia. There was also a marked decrease in exhaustion time (p < 0.01, 65% vs. normoxia) in hypoxia control rats, indicating a reduced work capacity. Exercise preconditioning along with NCF supplementation significantly increased the slow-oxidative fiber proportion and exhaustion time while maintaining mitochondrial homeostasis. These findings suggest that HH leads to an increased transition of slow-oxidative fibers to fast glycolytic fibers and increased muscular fatigue. Administration of NCF in combination with exercise preconditioning restored this myofiber remodeling and improved muscle anti-fatigue ability.

A Nanocurcumin and Pyrroloquinoline Quinone Formulation Prevents Hypobaric Hypoxia-Induced Skeletal Muscle Atrophy by Modulating NF-κB Signaling Pathway

Kushwaha, Asha D., and Deepika Saraswat. A nanocurcumin and pyrroloquinoline quinone formulation prevents hypobaric hypoxia-induced skeletal muscle atrophy by modulating NF-κB signaling pathway. High Alt Med Biol 00:000-000, 2022. Background: Hypobaric hypoxia (HH)-induced deleterious skeletal muscle damage depends on exposure time and availability of oxygen at cellular level, which eventually can limit human work performance at high altitude (HA). Despite the advancements made in pharmacological (performance enhancer, antioxidants) and nonpharmacological therapeutics (acclimatization strategies), only partial success has been achieved in improving physical performance at HA. A distinctive combination of nanocurcumin (NC) and pyrroloquinoline quinone (PQQ) has been formulated (named NCF [nanocurcumin formulation], Indian patent No. 302877) in our laboratory, and has proven very promising in improving cardiomyocyte adaptation to chronic HH. We hypothesized that NCF might improve skeletal muscle adaptation and could be a performance enhancer at HA. Material and Methods: Adult Sprague-Dawley rats (220 ± 10 g) were divided into five groups (n = 6/group): normoxia vehicle control, hypoxia vehicle control, hypoxia NCF, hypoxia NC, and hypoxia PQQ. All the animals (except those in normoxia) were exposed to simulated HH in a chamber at temperature 22°C ± 2°C, humidity 50% ± 5%, altitude 25,000 ft for 1, 3, or 7 days. After completion of the stipulated exposure time, gastrocnemius and soleus muscles were excised from animals for further analysis. Results: Greater lengths of hypoxic exposure caused progressively increased muscle ring finger-1 (MuRF-1; p < 0.01) expression and calpain activation (0.56 ± 0.05 vs. 0.13 ± 0.02 and 0.44 ± 0.03 vs. 0.12 ± 0.021) by day 7, respectively in the gastrocnemius and soleus muscles. Myosin heavy chain type I (slow oxidative) fibers significantly (p > 0.01) decreased in gastrocnemius (>50%) and soleus (>46%) muscles by the seventh day of exposure. NCF supplementation showed (p ≤ 0.05) tremendous improvement in skeletal muscle acclimatization through effective alleviation of oxidative damage, and changes in calpain activity and atrophic markers at HA compared with hypoxia control or treatment alone with NC/PQQ. Conclusion: Thus, NCF-mediated anti-oxidative, anti-inflammatory effects lead to decreased proteolysis resulting in mitigated skeletal muscle atrophy under HH.

Sphk1 promotes ulcerative colitis via activating JAK2/STAT3 signaling pathway

Ulcerative colitis (UC) is a chronic non-specific inflammatory disease of the colon and rectum. The cause of ulcerative colitis is still unclear, although there may be a hereditary factor. SphK1 has been reported to exhibit an inhibitory effect on the occurrence and development of inflammation; however, the association between SphK1 and the progression of UC remains unclear. The aim of the present study was to investigate the effect of Sphk1 on the progression of UC. The proliferation of RAW264.7 cells was determined using a Cell Counting Kit-8 assay and apoptosis was measured using flow cytometry. The levels of pro-inflammatory cytokines secreted by RAW264.7 cells were investigated using ELISA kits and the protein expression levels in RAW264.7 cells were examined by western blotting. A dextran sulfate sodium (DSS)-induced mouse model was established to investigate the effect of SphK1 on the progression of UC in vivo. Overexpression of Sphk1 significantly increased the proliferation and inhibited the apoptosis of RAW264.7 cells. Additionally, overexpression of Sphk1 increased the secretion of pro-inflammatory cytokines and activated the JAK2/STAT3 signaling pathway in RAW264.7 cells, and JSI-124 partially suppressed these effects. Furthermore, SphK1-small interfering RNA or JSI-124 partially rescued lipopolysaccharide-induced proliferation and pro-inflammatory effects on RAW264.7 cells. The SphK1 inhibitor (PF-543) had an inhibitory effect on DSS-induced UC mice. Sphk1 had significant pro-inflammatory effects on the progression of UC, and may thus be a potential novel therapeutic target for the treatment of UC.