Aging Effects on Cardiac Progenitor Cell Physiology

Cardiac aging has been confounded by the concept that the heart is a postmitotic organ characterized by a predetermined number of myocytes, which is established at birth and largely preserved throughout life until death of the organ and organism. Based on this premise, the age of cardiac cells should coincide with that of the organism; at any given time, the heart would be composed of a homogeneous population of myocytes of identical age. The discovery that stem cells reside in the heart and generate cardiac cell lineages has imposed a reconsideration of the mechanisms implicated in the manifestations of the aging myopathy. The progressive alterations of terminally differentiated myocytes, and vascular smooth muscle cells and endothelial cells may represent an epiphenomenon dictated by aging effects on cardiac progenitor cells (CPCs). Changes in the properties of CPCs with time may involve loss of self-renewing capacity, increased symmetric division with formation of daughter committed cells, partial depletion of the primitive pool, biased differentiation to the fibroblast fate, impaired ability to migrate, and forced entry into an irreversible quiescent state. Telomere shortening is a major variable of cellular senescence and organ aging, and support the notion that CPCs with critically shortened or dysfunctional telomeres contribute to myocardial aging and chronic heart failure. These defects constitute the critical variables that define the aging myopathy in humans. Importantly, a compartment of functionally competent human CPCs persists in the decompensated heart pointing to stem cell therapy as a novel form of treatment for the aging myopathy.