Lactateunraveling the regenerative potential for cardiac tissue engineering

Resumen

The increasing prevalence of cardiovascular diseases and their high health and socioeconomic impact on the world population urge the development of efficient new therapies for the reestablishment of the cardiac function. The heart has a very limited regenerative ability, and so lost cardiomyocytes cannot be replaced, thus causing permanent damage. These cells undergo different metabolic changes during development crucial for their maturation and adult function. During fetal development, proliferating cardiac cells reside in a low oxygen environment with high concentrations of lactate. After birth, cardiomyocytes cease their proliferating activity and shift their metabolism to fatty acid oxidation. Alterations of cardiac metabolism have also been associated with multiple disease states and pathological hypertrophy. Here in this work, we evaluated the response of cardiac cells to the presence of exogenous lactate, thus mimicking the metabolic microenvironment of early developmental stages.Lactate-exposed mouse primary cardiomyocytes and human iPSC-derived cardiomyocytes quickly acquired a characteristic dedifferentiated phenotype, with enhanced proliferative activity as determined by the expression of cell cycle (Ki67) and cytokinesis (AurB) effectors. We characterized lactate-induced cardiomyocyte dedifferentiation through RNA-sequencing and gene expression analysis and identified increased expression of BMP10 (involved in embryonic cardiomyocyte proliferation and stemness), LIN28 (a master regulator of stem cell fate and metabolism) and other genes associated to regulation of the stem cell fate (P63, TCIM or GATA4). On the other hand, we saw a downregulation of cardiac maturation genes related to lipid metabolism (DGKK) or electrical impulse regulation (GRIK1). Bottom-up analysis suggested the activation of hypoxia signaling pathways, indicating that, indeed, lactate may be a key player of hypoxic regenerative responses in the heart.Cardiomyocytes, however, are only 30-40% of the total population of cardiac cells. The majority of non-myocyte cells are comprised of cardiac fibroblasts and endothelial cells, whose interactions with cardiomyocytes highly contribute to heart repair and tissue homeostasis. Our results showed that lactate did not affect cardiac fibroblast proliferation, collagen production, migration or myofibroblast activation, which are detrimental factors for an effective cardiac regeneration. Lactate showed to reduce the expression of inflammatory cytokines involved in heart failure and cardiomyocyte apoptosis (Fas, Fractalkine or IL-12p40) and promote the production of healing and pro-regenerative signals (IL-13 and SDF-1a). In addition, endothelial precursor cells demonstrated their ability to use lactate as an effective energy source for survival and proliferation, even equivalent to the utilization of glucose. Taken together, the synergistic lactate response of the main cardiac cell types could enhance heart regeneration by supporting the growth and survival of new cardiomyocytes to repopulate the ischemic injury.Additionally, cardiac tissue constructs and ex vivo neonatal heart culture showed a more immature electromechanical behavior, with prolonged cardiac functions and improved proliferation as well as tissue integrity when culture media was supplemented with lactate. Thus, we explored the use of lactate-releasing cardiac scaffolds using different biomaterials, such as PLA, PLGA, alginate or conductive polymers, and different fabrication techniques, such as electrospinning; considering the fundamental aspects of cardiac scaffolds (anisotropy, flexibility and conductivity). These scaffolds proved to be an attractive and simple approach for a cardiac regenerative therapy.Altogether, the use of lactate as a metabolic modulator for the in situ activation of endogenous cardiac regenerative programs may revolutionize the design of new therapies for the treatment and regeneration of the failing heart.