Contrasting In Situ and In Vitro Expression of miR-155 and miR-146a in Astrocytes in Context of Multiple Sclerosis (MS) (P3.009)

Objective To measure expression of miR-155 and miR-146a in astrocytes from MS lesions and compare microRNA expression with astrocytes cultured under inflammatory and metabolic stress conditions Introduction - Increased astrocytic activity is a hallmark of MS lesions and plays a critical role in inflammation and significantly influences the extent of brain injury and repair. MicroRNA expression is altered in the inflamed central nervous system and can regulate astrocyte function. MiR-155 and miR-146a have been previously demonstrated to influence human astrocyte function. Methods - For in situ studies, GFAP+ astrocytes were laser micro-dissected from chronic active MS lesions; CD68+ macrophages/microglia were also dissected. Astrocytes were also derived from acute and chronic ischemic brain lesions and autopsy control tissues. For in vitro studies, cultures of 2nd trimester fetal human brain derived astrocytes were exposed to IL-1β or stress conditions (glucose/serum deprivation ± hypoxia). Results - In the MS lesion samples, miR-155 expression was comparable to control samples whereas expression was increased in myeloid cells (Moore et al., 2013. Annals of Neurology). Compared to controls, miR-146a expression was decreased in both astrocytes from MS lesions and ischemic samples, but not in microglia. In vitro, miR-155 and miR-146a expression was increased in astrocytes exposed to IL-1β; no changes were measured under stress conditions sufficient to induce release of FGF-1. Conclusions - In vitro results suggest that inflammation, rather than micro-environmental metabolic stress, is an inducer of miR-155 and miR-146a. The absence of miR-155 up-regulation in chronic active MS cases suggests that any temporal up-regulation of microRNA expression in astrocytes is not persistent and contrasts with results obtained from microglia. Although it is not unexpected that the anti-inflammatory miR-146a might be less expressed in an active lesion, the basis for this decrease remains to be defined. Disclosure: Dr. Rao has nothing to disclose. Dr. Ludwin has nothing to disclose. Dr. Fuh has nothing to disclose. Dr. Minderman has nothing to disclose. Dr. Sawaya has nothing to disclose. Dr. Moore has nothing to disclose. Dr. Ho has nothing to disclose. Dr. Bedell has received personal compensation for activities with Biospective Inc. Dr. Antel has received compensation for activities with Novartis, Sanofi/Genzyme Inc., Biogen Idec, EMD Serono, Juno Therapeutics, and MedDay for serving on the advisory boards. Dr. Antel has received personal compensation in an editorial capacity for Mul