Description
Human c-kit+ cardiac progenitor cells (hCPC) reduce scar size and improve left ventricular (LV) systolic function after adoptive transfer in human patients with heart failure. During cardiac aging, DNA damage and environmental stressors contribute to telomeric shortening, and hCPCs begin to acquire a senescent phenotype that leads to decreased stem cell function. Reversion of this phenotype through genetic modification is essential to advance regenerative therapy. Studies in the cardiac specific overexpression of Pim1 kinase demonstrate its effect on cellular processes involved in regeneration, proliferation, survival, metabolism and senescence. The findings of this study demonstrate for the first time that subcellular targeting of Pim1 preferentially highlights the cardioprotective effects of the kinase in hCPCs to increase proliferation and survival, supporting the reversion of a senescent phenotype. To effect proliferation and survival, hCPC were transduced with six different lentiviral vectors to express both control (GFP) and Pim1 specifically in the entire cell (PimWT), mitochondria (Mito-Pim1) or nuclear (Nuc-Pim1) compartment. Modified hCPCs showed differential rates of apoptosis after treatment with hydrogen peroxide as measured by flow cytometry. Analysis of apoptotic signaling proteins led to the conclusion that mitochondrial targeted Pim1 works synergistically with Bcl-2 and Bcl-XL proteins to inhibit apoptosis and preserve mitochondrial integrity far superior than PimWT alone. MitoPim1 also proved to be a more significant driver of proliferation than Nuc-Pim1 or PimWT in hCPCs. Mitochondrial localization results in increased proliferation and subsequent upregulation of modulators of cell cycle progression, two processes that could correlate with the stabilization of hCPC energy metabolism. Pim1 is also capable of rejuvenating diseased hCPCs to a youthful phenotype. In this study, nuclear-targeted Pim1 successfully blunts senescence of hCPCs relative to PimWT and Mito-Pim1. Nuc-Pim1 supports both phenotypic and biological changes in senescent hCPCs to enhance stem cell youthfulness associated with increased growth potential, telomere lengthening and reduced markers of senescence. This study demonstrates Pim1 localization can enhance proliferation, survival and youthful properties of aged human CPCs when expression is localized to both the nuclear or mitochondrial compartment of the cell. This study differentiates the cardioprotective roles of Pim1 based on intracellular localization and enhances the potential of Pim1 in the context of stem cell based cardiac regeneration.
