Trainee Lightning Talk: Hana Kalčo

Downhill Running Induces Anti-Inflammatory Signaling in Bone and Tendon

ABSTRACT

It is well-known that bone and muscle are coordinately regulated during aging and exercise. However, the effects of local crosstalk between joint tissues and the contribution of tendon to this process are still unexplored. In this study, we induced acute stress in muscle using a well- established mouse model of injury (downhill running) and explored the interactions with other tissues (tendon, bone) in the shoulder joint. We hypothesized that temporary inflammatory responses elicited in muscle by downhill running will lead to altered signaling in the adjacent tendon and bone. Young (13 months old) C57BL/6 mice performed an unaccustomed, acute bout of exercise by running on a motorized treadmill at a negative grade (i.e. downhill). The 70-min downhill running protocol consisted of 10 stages at a −22°grade, separated with 3-min rest periods to prevent exhaustion. Animals were euthanized at 24h or 48h after injury. Their shoulders were harvested for in vitro experiments where tissue monocultures (humerus, supraspinatus muscle, supraspinatus tendon) were maintained in basic culture medium for 24h. At the end of the culture, medium was collected and used for proteomic analysis of secreted proteins using the MSD Mouse Pro-Inflammatory 10-Plex multi-spot assay to quantify levels of IFN-γ, IL-10,IL-15,IL-1β, IL-4, IL- 6, KC/GRO, MCP-1 and TNF-α. The gene expression of key tissue-specific markers of muscle (IGF-1, IL-6, FGF 21), bone (Sost, BGLP, PGE-2) and tendon (IL-6, IL-1b,TNF-a) was measured via RT-qPCR. Expression for each gene was calculated from the threshold cycle (Ct) value and normalized to an internal housekeeping gene (β-Actin).

We found that muscle exhibits increased gene expression of IL-6 soon after downhill running (Fig.1A), but tendon- or bone-specific genes were not differentially expressed from baseline. Tendon and bone both produce significantly increased levels of inflammatory proteins, including IL-4, IL-6, and IL-15, at 48h post-running (Fig.1B). These findings support our hypothesis that the response to downhill running in tendon and bone is subsequent to the muscle response. High levels of anti-inflammatory proteins secreted by bone and tendon appear to antagonize the expression and activities of pro-inflammatory cytokines to prevent muscle atrophy and adverse metabolic effects while facilitating regeneration. Therefore, we believe coordinated responses of all three tissues are critical for the resolution of inflammation in the context of acute muscle stress.

Hana Kalčo1, Paola Divieti Pajevic2, LaDora V. Thompson3, Brianne K. Connizzo1

1Department of Biomedical Engineering, Boston University, Boston, MA
2Boston University Henry M. Goldman School of Dental Medicine
3Sargent College, Boston University, Boston, MA