Protection against Glucocorticoid-Induced Damage in Human Tenocytes by Modulation of ERK, Akt, and Forkhead Signaling

Antiinflammatory glucocorticoid (GC) injections are extensively used to treat painful tendons. However, GC cause severe tissue wasting in other collagen-producing tissues such as skin and bone. The objective of this study was to determine the effects of GC on tenocytes and to explore strategies to protect against unwanted side effects of GC treatment. Cell survival, collagen production, and the induction of signaling pathways in primary human tenocytes treated with dexamethasone (Dex) were assessed. Antioxidant and growth factor approaches to protection were tested. Dex treatment resulted in reduced viable cell number, cell proliferation, and collagen production. Dex induced reactive oxygen species generation in tenocytes and strongly up-regulated the stress-response transcription factors FOXO1 and FOXO3A. Phosphorylation of ERK and protein kinase B/Akt, which regulate cell proliferation and also inhibit forkhead activity, was decreased. Chemical inhibition of ERK or Akt activity significantly reduced tenocyte cell number. Ameliorating the Dex-induced reduction in ERK or Akt activity by cotreatment with vitamin C or insulin protected against the Dex-induced reduction in cell number. Silencing FOXO1 prevented the Dex-induced reduction in collagen 1α1 expression. Cotreatment with vitamin C or insulin protected against the Dex-induced increase in FOXO and the Dex-induced inhibition of collagen 1α1 expression. Reduced ERK and Akt activation and increased forkhead signaling contribute to the negative effects of GC on tenocytes. Cotreatment therapies that target these signaling pathways are protective. Vitamin C in particular may be a clinically useable co-therapy to reduce connective tissue side effects associated with GC therapy.