Gregg, Savannah R.Barshick, Madison R.Johnson, Sally E.2023-10-132023-10-132023-09-27Gregg, S.R.; Barshick, M.R.; Johnson, S.E. Intravenous Injection of Sodium Hyaluronate Diminishes Basal Inflammatory Gene Expression in Equine Skeletal Muscle. Animals 2023, 13, 3030.http://hdl.handle.net/10919/116463Following strenuous exercise, skeletal muscle experiences an acute inflammatory state that initiates the repair process. Systemic hyaluronic acid (HA) is injected to horses routinely as a joint anti-inflammatory. To gain insight into the effects of HA on skeletal muscle, adult Thoroughbred geldings (n = 6) were injected with a commercial HA product weekly for 3 weeks prior to performing a submaximal exercise test. Gluteal muscle (GM) biopsies were obtained before and 1 h after exercise for gene expression analysis and HA localization. The results from RNA sequencing demonstrate differences in gene expression between non-injected controls (CON; n = 6) and HA horses. Prior to exercise, HA horses contained fewer (<i>p</i> < 0.05) transcripts associated with leukocyte activity and cytokine production than CON. The performance of exercise resulted in the upregulation (<i>p</i> < 0.05) of several cytokine genes and their signaling intermediates, indicating that HA does not suppress the normal inflammatory response to exercise. The transcript abundance for marker genes of neutrophils (<i>NCF2</i>) and macrophages (<i>CD163</i>) was greater (<i>p</i> < 0.05) post-exercise and was unaffected by HA injection. The anti-inflammatory effects of HA on muscle are indirect as no differences (<i>p</i> > 0.05) in the relative amount of the macromolecule was observed between the CON and HA fiber extracellular matrix (ECM). However, exercise tended (<i>p</i> = 0.10) to cause an increase in ECM size suggestive of muscle damage and remodeling. The finding was supported by the increased (<i>p</i> < 0.05) expression of <i>CTGF</i>, <i>TGFβ<sub>1</sub></i>, <i>MMP9</i>, <i>TIMP4</i> and <i>Col4A1</i>. Collectively, the results validate HA as an anti-inflammatory aid that does not disrupt the normal post-exercise muscle repair process.application/pdfenCreative Commons Attribution 4.0 Internationalequineskeletal muscleexercisehyaluronic acidinflammationIntravenous Injection of Sodium Hyaluronate Diminishes Basal Inflammatory Gene Expression in Equine Skeletal MuscleArticle - Refereed2023-10-13Animalshttps://doi.org/10.3390/ani13193030