The Transient Receptor Potential Vanilloid 2 Cation Channel Is Abundant in Macrophages Accumulating at the Peri-Infarct Zone and May Enhance Their Migration Capacity towards Injured Cardiomyocytes following Myocardial Infarction

PURPOSE A novel family of transient receptor potential (TRP) channels, that may hold a role in calcium homeostasis, has recently been described. By employing a GeneChip array analysis we have demonstrated a clear and specific upregulation of the TRP vanilloid 2 (TRPV2) mRNA in the left ventricles (LV) 3-5 days post-acute myocardial infarction (MI) compared to sham-operated controls, both in rats and in mice. We sought to characterize the cardiac cellular subpopulations in which TRPV2 is overexpressed upon acute MI. METHODS Lewis rats underwent an acute MI by ligation of the left anterior descending artery or chest opening only (sham). The animals were terminated at various time points and an immunohistochemical (IHC) and immunofluorescent (IFC) staining of the LV sections as well as a flow cytometry analysis of LV-derived cells were carried out, using anti-TRPV2 and anti-monocyte/macrophage antibodies. Rat alveolar macrophage cells, NR8383, transiently transfected with TRPV2 siRNA were allowed to migrate towards hypoxic conditioned media of the rat cardiac myoblast line H9C2 using a trans-well migration assay. The macrophage cells migrating to the bottom side of the inserts were counted. RESULTS The IHC and IFC staining as well as the flow cytometry data demonstrated a substantial expression of TRPV2 in infiltrating macrophages in the peri-infarct region 3-5 days post-acute MI. The in vitro migration assay data demonstrated that following inhibition of the TRPV2 channel, the number of migrating macrophages towards conditioned medium of hypoxic cardiomyocytes was significantly reduced. CONCLUSIONS TRPV2 is highly expressed on the peri-infarct infiltrating macrophages and may play an important role in post-MI phagocytosis. Better characterization of this channel may pave the way for identifying a new target for modulating the dramatic post-MI immune reactions.