Abstract P3062: T-cell Myd88 Regulates Cardiac Fibrosis In Heart Failure By Modulating T-cell Survival And Pro-inflammatory Signaling

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Background: Despite the association of heart failure (HF) with cardiac and systemic inflammation, anti-inflammatory therapies have shown limited success. Cardiac inflammation is characterized by the presence of damage associated molecular patterns (DAMPs), myeloid and T-helper cell infiltration, and the activation of cardiac fibroblasts (CFB). The adaptor “Myeloid differentiation response 88” (MyD88) is central to DAMP sensing in myeloid cells, but its role in T-cell function and cardiac inflammation is largely unknown. We hypothesized that T-cell signaling through MyD88 modulates cardiac inflammation and fibrosis in HF. Methods and Results: We reconstituted T-cell deficient ( Tcra -/- ) mice, normally protected from cardiac fibrosis, with WT or Myd88 -/- Type 1 helper T-cells (Th1) in the onset of transaortic constriction (TAC). We found mice given Myd88 -/- Th1 cells exhibited significantly higher levels of cardiac T-cell infiltration, increased cardiac fibrosis, and lower fractional shortening than mice given WT Th1 cells. T-cell specific MyD88 deficient mice ( Myd88 fl/fl CD4 Cre ) also developed more fibrosis and increased cardiac T-cells compared to Cre- littermate controls in response to TAC. RNA-seq analysis of WT and Myd88 -/- Th1 cells revealed enrichment of pro-inflammatory signaling and pro-survival genes in Myd88 -/- Th1 cells, which we validated by immunoblotting for phospho-ERK, NF-kB, and AKT. In contrast, IFNγ, the Th1 signature cytokine, was similar by qPCR and flow cytometry in WT and Myd88 -/- cells. Moreover, we discovered that Myd88 -/- Th1 cells have increased survival in vitro, by monitoring propidium iodide incorporation in real time, and in vivo by adoptive transfer of equal numbers of WT and Myd88 -/- cells together into Tcra -/- mice and quantifying both cell types in lymphoid organs over time. Lastly, more Myd88 -/- Th1 cells adhered to immobilized VCAM-1 and CFB in vitro compared to WT, resulting in enhanced CFB transformation. Conclusion: T-cell MyD88 limits cardiac fibrosis in TAC through modulation of T-cell inflammatory signaling and cell survival. Disruption of this pathway in T-cells results in enhanced transformation of fibroblasts and worsened systolic function.