Cardiac stem cell niches

• The adult heart contains stem cell niches.
• The c-kit receptor identifies a pool of resident cardiac stem cells.
• Hypoxic and normoxic niches coexist in the myocardium.
• Cardiac mesenchymal stem cells are nested in perivascular niches.

The critical role that stem cell niches have in cardiac homeostasis and myocardial repair following injury is the focus of this review. Cardiac niches represent specialized microdomains where the quiescent and activated state of resident stem cells is regulated. Alterations in niche function with aging and cardiac diseases result in abnormal sites of cardiomyogenesis and inadequate myocyte formation. The relevance of Notch1 signaling, gap-junction formation, HIF-1α and metabolic state in the regulation of stem cell growth and differentiation within the cardiac niches are discussed.