The hypoxic epicardial and subepicardial microenvironment.

Area of Science:

• Cardiovascular Biology
• Stem Cell Biology
• Cellular Metabolism

Background:

• The adult mammalian heart exhibits limited cardiomyocyte turnover, with the epicardium and subepicardium emerging as potential sources of cardiac stem/progenitor cells.
• Stem cell niches often feature low oxygen tension (hypoxia), where cells utilize glycolysis for energy. However, the presence and metabolic characteristics of such niches within the heart remain unclear.

Purpose of the Study:

• To identify and characterize hypoxic niches within the uninjured adult mammalian heart.
• To determine if these niches contain metabolically distinct cardiac progenitor populations.
• To investigate the role of hypoxia signaling, specifically Hypoxia-inducible factor-1α (Hif-1α), in regulating cardiac progenitor cells.

Main Methods:

• Quantification of capillary density to assess tissue oxygenation.
• Localization of Hif-1α expression in the uninjured heart.
• Metabolic profiling of cardiac progenitor cells within identified niches.
• Functional assays to assess progenitor properties and the impact of Hif-1α.

Main Results:

• The epicardium and subepicardium were identified as the cardiac hypoxic niche based on reduced capillary density and Hif-1α localization.
• A distinct population of metabolically glycolytic progenitor cells resides within this hypoxic microenvironment.
• Hif-1α was shown to regulate the glycolytic phenotype and progenitor characteristics of these cardiac cells.

Conclusions:

• The epicardial and subepicardial microenvironment constitutes a functionally significant hypoxic niche in the heart.
• This niche harbors a unique population of cardiac progenitor cells with a glycolytic metabolic profile.
• Hypoxia signaling, mediated by Hif-1α, plays a crucial role in regulating the properties of cardiac progenitors within this niche.