Dexamethasone-Induced Skeletal Muscle Atrophy Increases O-GlcNAcylation in C2C12 Cells

Skeletal muscle atrophy is a well-known adverse effect of chronic treatment with glucocorticoids and it also occurs when stress conditions such as sepsis and cachexia increase the release of endogenous glucocorticoids. Although the mechanisms of action of these hormones have been elucidated, the possible molecular mechanisms causing atrophy are not yet fully understood. The involvement of the O-GlcNAcylation process has recently been reported in disuse atrophy. O-GlcNAcylation, a regulatory post-translational modification of nuclear and cytoplasmic proteins consists in the attachment of O-GlcNAc residues on cell proteins and is regulated by two enzymes: O-GlcNAc-transferase (OGT) and O-GlcNAcase (OGA). O-GlcNAcylation plays a crucial role in many cellular processes and it seems to be related to skeletal muscle physiological function. The aim of this study is to investigate the involvement of O-GlcNAcylation in glucocorticoid-induced atrophy by using an "in vitro" model, achieved by treatment of C2C12 with 10 μM dexamethasone for 48 h. In atrophic condition, we observed that O-GlcNAc levels in cell proteins increased and concomitantly protein phosphorylation on serine and threonine residues decreased. Analysis of OGA expression at mRNA and protein levels showed a reduction in this enzyme in atrophic myotubes, whereas no significant changes of OGT expression were found. Furthermore, inhibition of OGA activity by Thiamet G induced atrophy marker expression. Our current findings suggest that O-GlcNAcylation is involved in dexamethasone-induced atrophy. In particular, we propose that the decrease in OGA content causes an excessive and mostly durable level of O-GlcNAc residues on sarcomeric proteins that might modify their function and stability. J. Cell. Biochem. 117: 1833-1842, 2016. © 2016 Wiley Periodicals, Inc.

MicroRNA expression profile of dexamethasone-induced human bone marrow-derived mesenchymal stem cells during osteogenic differentiation

MiRNAs have been identified in various plants and animals where they function in post-transcriptional regulation. Although studies revealed that dexamethasone play a pivotal role in the osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs), the identification of specific miRNAs and their regulatory roles in this process remain poorly defined. In this study, microarrays were used to analyze the miRNA expression profile of dexamethasone-induced hBMSCs derived from three donors, and RT-PCRs were used to confirm the microarray results. Nine upregulated miRNAs and seven downregulated miRNAs were identified. The putative target genes of these miRNAs were predicted using bioinformatics analysis. Subsequently, we focused our attention on the functional analysis of an upregulated miRNA, miR-23a. Overexpression of miR-23a inhibited osteogenic differentiation of hBMSCs at the cellular, mRNA, and protein levels. The results of our study provide an experimental basis for further research on miRNAs functions during osteogenic differentiation of dexamethasone-induced hBMSCs.

Studies on wound healing

Factors affecting the rate of healing of experimental skin wounds in rats have been investigated. The effectiveness of healing was measured by determining the tensile strengths of the incised skin after various time intervals. When the skin histamine content was lowered by treatment with polymyxin B or with compound 48/80, retardation of the healing process was evident from the reduced tensile strengths. When the skin 5-hydroxytryptamine content was lowered by treatment with reserpine, retardation of healing was also found. Heparin increased the rate of healing and more rapid healing was obtained by giving histamine before each dose of heparin. On the other hand, some glucocorticoids markedly inhibited the healing process. Of the constituents of the tissue mast cells, heparin appears to be more important than histamine and 5-hydroxytryptamine in promoting the healing of experimental skin wounds in rats.

Effects of dexamethasone, prednisolone and cortisol on the mast cells and tissue eosinophils in rat gastric mucosa

Intact rats were injected intramuscularly at 8-hourly intervals with equal amounts, 6×1.0 mg, of dexamethasone (16α-methyl-9α-fluoro-prednisolone) as phosphate, prednisolone (11β,17,21-trihydroxy-pregna-1,4-diene-3,20-dione) and cortisol (11β,17,21-trihydroxy-pregn-4-ene-3,20-dione) both as succinates, all three in water soluble form. The rats were decapitated 4 hours after the last injection and the mucosal mast cells and tissue eosinophilic cells in the body mucosa of the glandular stomach counted. Calculation of the mast cell degranulation and the destruction of tissue eosinophils during the experiment gave the following degranulation coefficients for the degranulation of gastric mucosal mast cells: 0.541 for dexamethasone, 0.177 for prednisolone and 0.088 for cortisol. The corresponding destruction coefficients for the loss of tissue eosinophilia were 0.858, 0.156 and 0.124.

It is suggested that the degranulation and destruction coefficients obtained in the investigation are correlated with the catabolic biological activity of the glucocorticoids.

CHEMOTHERAPY OF ARTHRITIS INDUCED IN RATS BY MYCOBACTERIAL ADJUVANT

Arthritis induced in rats by mycobacterial adjuvant has been used for the study of compounds of known value in the treatment of rheumatoid arthritis in man. The development of the arthritic syndrome in treated and control rats was followed by measuring the changes in foot thickness of both hind-feet with a micrometer. This method allowed the effect of anti-inflammatory compounds to be expressed quantitatively. Anti-inflammatory activity was readily observed in certain steroids, pyrazolidines, salicylates and sodium aurothiomalate. Chloroquine and hydroxychloroquine were inactive. The inhibition obtained by daily treatment with the steroid paramethasone disappeared when treatment was withdrawn.