Abstract 264: TNFR2-Bmx Signaling in Cardiac Stem Cells and Cardiac Repair

Abstract

While cytokine TNF via TNFR1 induces inflammation and apoptosis, it through its second receptor TNFR2 induces cell survival and migration by activating bone marrow non-receptor tyrosine kinase Bmx. Since Bmx has been implicated in self-renewal of stem cells, we hypothesize that TNF via TNFR2 activates Bmx in cardiac stem cells (CSCs) to mediate cardiac repair. We show that in human cardiac tissue affected by ischemia heart disease (IHD), TNFR2 is expressed on intrinsic CSCs, identified as c-kit(+) /CD45(-) /VEGFR2(-) interstitial round cells, which are activated as determined by entry to cell cycle and expression of Lin-28. Wild-type mouse heart organ cultures subjected to hypoxic conditions both increase cardiac TNF expression and show induced TNFR2 and Lin-28 expression in c-kit(+) CSCs that have entered cell cycle. These CSC responses are enhanced by exogenous TNF. TNFR2(-/-) mouse heart organ cultures subjected to hypoxia increase cardiac TNF but fail to induce CSC activation. Similarly, c-kit(+) CSCs isolated from mouse hearts exposed to hypoxia or TNF show induction of Lin-28, TNFR2, cell cycle entry, and cardiogenic marker, α-sarcomeric actin (α-SA), responses more pronounced by hypoxia in combination with TNF. Knockdown of Lin-28 by siRNA results in reduced levels of TNFR2 expression, cell cycle entry, and diminished expression of α-SA (references: Stem Cells 2013;31:1881-1892). In the present study, we detect the c-kit(+)Lin28(+) CSCs populations in a mouse coronary artery ligation ischemic model. Furthermore, the c-kit(+) CSCs are reduced in TNFR2-KO and Bmx-KO mice. Mechanistically, we show a crosstalk between the TNFR2-Bmx and the c-Kit signaling pathways to mediate CSC proliferation, survival and migration. These observations suggest that TNFR2-Bmx signaling in c-kit(+) CSCs induces cardiac repair, providing a potential strategy to stimulate cardiac regeneration by TNFR2-specific agonists.