New insights into the pathogenesis of glucocorticoid-induced avascular necrosis: microarray analysis of gene expression in a rat model

Mohammad Amin Kerachian,Terry Y Chow,Denis Cournoyer,Louis R Bégin,Edward J Harvey,Chantal Séguin,Ayoub Nahal

doi:10.1186/ar3062

Abstract

IntroductionAvascular necrosis of the femoral head (ANFH) occurs variably after exposure to corticosteroids. Microvascular thrombosis is a common pathological finding. Since systemic thrombophilia is only weakly linked with ANFH, we propose that microvascular vessel pathology may be more related to local endothelial dysfunction and femoral head apoptosis. Corticosteroid effects on the endothelium and resultant apoptosis have been reported. We hypothesize that corticosteroids contribute to a differential gene expression in the femoral head in rats with early ANFH.MethodsBesides bone marrow necrosis, which is a common sign in ANFH and reported in the early stages, we include the presence of apoptosis in this study as a criterion for diagnosing early disease. Forty Wistar Kyoto (WKY) rats were randomized to either a corticosteroid-treated group or an age-matched control group for six months. After sacrifice, the femoral heads were examined for ANFH. Total mRNA was extracted from femoral heads. Affymetrix exon array (Santa Clara, CA, USA) was performed on 15 selected RNA samples. Validation methods included RT-PCR and immunohistochemistry (IHC).ResultsAlthough rat exon array demonstrated a significant upregulation of 51 genes (corticosteroid(+)/ANFH(+) VS control), alpha-2-macroglobulin (A2M) gene was particularly over-expressed. Results were validated by RT-PCR and IHC. Importantly, A2M is known to share vascular, osteogenic and cartilage functions relevant for ANFH.ConclusionsThe findings suggest that corticosteroid-induced ANFH in rats might be mediated by A2M. Investigation of A2M as a potential marker, and a treatment target, for early ANFH should be carried out.

Highlights

Avascular necrosis of the femoral head (ANFH) occurs variably after exposure to corticosteroids
The use of the TUNEL assay to detect apoptosis showed apoptotic osteocytes were located in the osteonecrotic samples without features of inflammation and visible necrosis, such as hyperemia, round cell infiltration, or lipid cyst formation
Microarray analysis In the Affymetrix analysis, group 2 (G2) replicates were compared with group 1 (G1) and group 3 (G3), separately, and G3 replicates were compared with G1 to generate a list of differentially expressed genes

Summary

Introduction

Avascular necrosis of the femoral head (ANFH) occurs variably after exposure to corticosteroids. Since systemic thrombophilia is only weakly linked with ANFH, we propose that microvascular vessel pathology may be more related to local endothelial dysfunction and femoral head apoptosis. Corticosteroid effects on the endothelium and resultant apoptosis have been reported. We hypothesize that corticosteroids contribute to a differential gene expression in the femoral head in rats with early ANFH. ANFH is a potential major complication for large patient populations Investigators have proposed both direct and indirect effects of GCs on cells. We propose that the microvascular events could be more related to endothelial dysfunction and diffuse femoral head apoptosis. Based on reported data on corticosteroid effects on the endothelium and their role in apoptosis, we hypothesized that corticosteroids contribute to a differential gene expression in rats with early ANFH

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Discussion

Conclusion