Chondrocytes Contribute to Alphaviral Disease Pathogenesis as a Source of Virus Replication and Soluble Factor Production

Arthritogenic alphavirus infectionsoften result in debilitating musculoskeletal disordersthat affect the joints, muscle, and bone. In order to evaluate the infection profile of primary human skeletal muscle and chondrocytecells to Ross River virus(RRV) in vitro, cells were infected at a multiplicityof infection(MOI) of 1 over a period of two days. Viral titers were determined by plaque assay and cytokine expression by Bio-Plex® assays using the supernatants harvested. Gene expression studies were conducted using total RNA isolated from cells. Firstly, we show that RRV RNA is detected in chondrocytesfrom infected mice in vivo. Both human primary skeletal muscle and chondrocytecells are able to support productive RRV infection in vitro. We also report the production of soluble host factorsincluding the upregulation of heparanase(HPSE) and inflammatory host factorssuch as interleukin-6 (IL-6), monocyte chemoattractant protein 1 (MCP-1), RANTES (regulated on activation, normal T cell expressed and secreted), interferon gamma(IFN-γ), and tumor necrosis factor alpha (TNF-α), which are also present during clinical disease in humans. Our study is the first to demonstrate that human chondrocytecells are permissive to RRV infection, support the production of infectious virus, and produce soluble factors including HPSE, which may contribute to joint degradation and the pathogenesis of disease.