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Rationale: The regenerative capacity of the heart is markedly diminished shortly after birth, coinciding with overall withdrawal of cardiomyocytes from cell cycle. Consequently, the adult mammalian heart has limited capacity to regenerate after injury. The discovery of factors that can induce cardiomyocyte proliferation is, therefore, of high interest and has been the focus of extensive investigation throughout the past years. Objective: We have recently identified C3orf58 as a novel hypoxia and Akt induced stem cell factor (HASF) secreted from mesenchymal stem cells, which can promote cardiac repair through cytoprotective mechanisms. Here, we tested the hypothesis that HASF can also contribute to cardiac regeneration by stimulating cardiomyocyte division and proliferation. Methods and Results: Neonatal ventricular cardiomyocytes were stimulated in culture for 7 days with purified recombinant HASF protein. Compared with control untreated cells, HASF-treated neonatal cardiomyocytes exhibited 60% increase in DNA synthesis as measured by bromodeoxyuridine incorporation. These results were confirmed by immunofluorescence confocal microscopy showing a 50% to 100% increase in the number of cardiomyocytes in the mitotic and cytokinesis phases. Importantly, in vivo cardiac overexpression of HASF in a transgenic mouse model resulted in enhanced level of DNA synthesis and cytokinesis in neonatal and adult cardiomyocytes. These proliferative effects were modulated by a phosphoinositide 3-kinase–protein kinase B–cycle-dependent kinase 7 pathway as revealed by the use of phosphoinositide 3-kinase -pathway–specific inhibitors and silencing of the Cdk7 gene. Conclusions: Our studies support the hypothesis that HASF induces cardiomyocyte proliferation via a phosphoinositide 3-kinase–protein kinase B–cycle-dependent kinase 7 pathway. The implications of this finding may be significant for cardiac regeneration biology and therapeutics.

Purpose: Brain angiogenesis inhibitor (BAI1) facilitates phagocytosis and bacterial pathogen clearance by macrophages; however, its role in viral infections is unknown. Here, we examined the role of BAI1, and its N-terminal cleavage fragment (Vstat120) in antiviral macrophage responses to oncolytic herpes simplex virus (oHSV). Experimental Design: Changes in infiltration and activation of monocytic and microglial cells after treatment of glioma-bearing mice brains with a control (rHSVQ1) or Vstat120-expressing (RAMBO) oHSV was analyzed using flow cytometry. Co-culture of infected glioma cells with macrophages or microglia was used to examine antiviral signaling. Cytokine array gene expression and Ingenuity Pathway Analysis (IPA) helped evaluate changes in macrophage signaling in response to viral infection. TNFα-blocking antibodies and macrophages derived from Bai1−/− mice were used. Results: RAMBO treatment of mice reduced recruitment and activation of macrophages/microglia in mice with brain tumors, and showed increased virus replication compared with rHSVQ1. Cytokine gene expression array revealed that RAMBO significantly altered the macrophage inflammatory response to infected glioma cells via altered secretion of TNFα. Furthermore, we showed that BAI1 mediated macrophage TNFα induction in response to oHSV therapy. Intracranial inoculation of wild-type/RAMBO virus in Bai1−/− or wild-type non–tumor-bearing mice revealed the safety of this approach. Conclusions: We have uncovered a new role for BAI1 in facilitating macrophage anti-viral responses. We show that arming oHSV with antiangiogenic Vstat120 also shields them from inflammatory macrophage antiviral response, without reducing safety. Clin Cancer Res; 23(7); 1809–19. ©2016 AACR.