No abstract

Eccentric contraction (EC) is known to elicit inflammation and damage in skeletal muscle. Proinflammatory cytokine TNF-alpha plays an important role in this pathogenesis, but the time course of its response to EC and the regulatory mechanisms involved are not clear. The purpose of the study is twofold: 1) to investigate the gene expression of TNF-alpha in rat muscle during and after an acute bout of downhill running and the associated oxidoreductive (redox) changes; and 2) to examine whether EC activates muscle ubiquitin-proteolytic pathway resulting in necrosis and oxidative damage. Female Sprague-Dawley rats (age 3 mo) were randomly divided into five groups (n = 6) that ran on treadmill at 25 m/min at -10% grade for 1 h (group 1) or 2 h (group 2) and were killed immediately; ran for 2 h and killed at 6 h after exercise (group 3), ran for 2 h and killed at 24 h after exercise (group 4); and killed at rest as controls (group 5). TNF-alpha mRNA and protein content showed progressive increases in the deep portion of vastus lateralis (DVL) and gastrocnemius muscles during and after EC. These changes were accompanied by a progressive decrease of mitochondrial aconitase activity and NF-kappaB activation. After 2 h of exercise, elevated levels of serum TNF-alpha, endotoxin, creatine kinase, and lipid peroxidation marker were evident and persisted through 24 h postexercise. At 24 h, there were marked increases in H(2)O(2) concentration, myleoperoxidase activity, and endotoxin level, along with nuclear accumulation of p65, in both muscles. mRNA level of ubiquitin-conjugating enzymes (E(2))-14k was progressively upregulated during exercise and recovery, whereas the expression of the Toll-like receptor 4 (TLR4) in DVL was downregulated in both muscles. We conclude that prolonged EC induces TNF-alpha expression possibly due to NF-kappaB activation stimulated by increased reactive oxygen species generation and endotoxin release. These inflammatory and prooxidative responses may underlie the processes of muscle proteolysis and oxidative damage.

No abstract

LEPTIN (LEP) is a circulating hormone released primarily from white adipocytes and is crucial for regulating satiety and energy homeostasis in humans and animals. Using the CRISPR technology, we created a set of Lep mutant rats that carry either null mutations or a deletion of the 14th Ile (LEP∆I14) in the mature LEP protein. We examined the potential off-target sites (OTS) by whole-genome high-throughput sequencing and/or Sanger-sequencing analysis and found no OTS in mutant rats. Mature LEP∆I14 is incessantly produced and released to blood at a much elevated level due to the feedback loop. Structure modeling of binding conformation between mutant LEP∆I14 and LEPTIN receptor (LEPR) suggests that the conformation of LEP∆I14 impairs its binding with LEPR, consistent with its inability to activate STAT3-binding element in the luciferase reporter assay. Phenotypic study demonstrated that Lep∆I14 rats recapitulate phenotypes of Lep-null mutant rats including obesity, hyperinsulinemia, hepatic steatosis, nephropathy, and infertility. Compared to the existing ob/ob mouse models, this Lep∆I14/∆I14 rat strain provides a robust tool for further dissecting the roles of LEP in the diabetes related kidney disease and reproduction problem, beyond its well established function in regulating energy homeostasis.