Metabolism and Control of Stem Cell Differentiation
The recent advances in the pluripotent stem cell biology now make it possible to generate human cardiomyocytes in vitro from both healthy individuals and from patients with cardiac abnormalities. This offers unprecedented opportunities to study cardiac disease development in a very controlled setting and establish novel platforms for drug discovery. However, to date, there are almost no studies evaluating the role of mitochondrial function and dynamics in the metabolism of human induced pluripotent stem cells (iPSC) and how these processes affect cardiomyocyte commitment. Our laboratory is currently studying the implications of mitochondrial dynamics and function in a model of iPSC of patients with Down syndrome and how this affects the differentiation of these cells into cardiovascular lineages.
Molecular Signal Transduction Laboratory
Regulation of mitochondrial function and morphology and cardiovascular diseases
Over the last 20 years, the view of cardiac and vasculature muscles as inert tissues that performs contractile activity has been replaced with the concept that cardiac and vasculature muscle mass and metabolism are highly dynamic. Cardiovascular remodeling is a complex process, which involves genetic, molecular and cellular changes in the heart and vascular tissues. In the heart, this process leads to progressive structural and functional alterations, including pathological cardiac hypertrophy, cardiac dilatation, interstitial fibrosis, and a reduction in contractility and relaxation. Vascular remodeling involves changes in cell growth, cell death, cell migration, and production or degradation of extracellular matrix, mainly by the vascular smooth muscle cells (VSMC). These processes are usually initiated as an adaptive process but may subsequently contribute to the pathophysiology of cardiovascular diseases. Common underlying mechanisms include physical stress (myocardial and vasculature stretch), neurohumoral and cytokine activation. Therapies aiming to counteract these mechanisms (i.e. angiotensin I converting enzyme inhibitors and antagonists of the beta-adrenergic receptor, AT1 receptor and aldosterone receptor) have proven successful in attenuating or even preventing cardiovascular remodeling. However, despite such success, these therapies have not succeeded in reducing in the progression of heart failure. Recently, cardiovascular metabolism has emerged as a new mechanism involved in the genesis and progression of cardiovascular diseases. In our laboratory, we study how a metabolic shift occurs in cardiac cells and VSMC and how these changes are involved in the genesis and development of cardiovascular diseases.
Mitochondrial dynamics, i.e. mitochondrial fusion and fission, are tightly associated with mitochondrial function and bioenergetics. Because cardiomyocytes require a constant supply of oxygen and ATP in order to maintain contractile function, alterations in mitochondrial function generate heart failure. In contrast, VSMC proliferation requires a decrease in mitochondrial activity in order to promote metabolite biosynthesis by using glycolytic intermediates. We explore whether mitochondrial dynamics may regulate cardiomyocyte and VSMC remodeling. We have shown that mitochondrial fission induces cardiomyocyte hypertrophy and VSMC dedifferentiation and proliferation associated with a decrease in mitochondrial metabolism.
We have recently published that during early phase of tunicamycin-induced endoplasmic reticulum (ER) stress, both ER and mitochondria increased intraorganelle interactions, thereby boosting metabolism as an adaptive mechanism. These changes were paralleled by a higher rate of oxygen consumption, suggesting an increase in mitochondrial bioenergetics. We studied whether the communication between mitochondria and ER can also be involved in the genesis and progression of cardiovascular diseases.
For mitochondrial dynamics and cardiovascular diseases, read:
Cardiomyocyte death mechanisms and Cardioprotection
Loss of cardiomyocytes due to cell death is an important causative factor in the development of heart failure. Therefore, one of our goal is to study the different mechanisms by which cardiomyocytes die and then disappear from the tissue. Our results have revealed that death by apoptosis, necrosis and/or autophagy is differentially induced in cardiomyocytes, depending on the nature of the insult (hyper- and hyposmotic stress, nutrient deprivation, testosterone and ceramides) to which these cells are exposed.
For more information of cell death in the cardiovascular system, please read:
Future development in cardioprotection will require the identification of molecules that protect cardiac cells from cell death. The most promising agents in this respect are growth factors, such as insulin like growth factor-1 (IGF-1) and angiotensin-(1-9). Here again, we study the mechanisms contributing to cardioprotection.
We previously showed that IGF-1 is a cardioprotective peptide. IGF-1 also increases cardiac DNA, protein synthesis, reduces protein degradation, and participates in neonatal cardiac myocyte maturation. We and others demonstrated that IGF-1 induced cardiac myocyte hypertrophy is associated with reexpression of fetal contractile proteins. Activation of both IGF-1 and insulin receptors lead to the stimulation of two major signaling pathways. One involves sequential activation of Ras/Raf-1/MEK/ERK pathway, which is linked to cell growth and proliferation. The other involves activation of phosphatidylinositol 3-kinase (PI3K) and AKT, linked to cell metabolism, growth, and anti-apoptotic responses. AKT phosphorylates and activates the mammalian target of rapamycin (mTOR) kinase, which in turn is responsible for increasing protein synthesis via p70-S6 kinase (p70-S6K). This signaling pathway is relevant in all models of IGF-1 dependent cardiac hypertrophy. We also identified a novel signaling pathway for IGF-1 in cardiac myocytes involving a fast and transient Ca2+i increase via activation of a heterotrimeric G protein-phospholipase C-IP3/IP3 receptor pathway. In cardiac myocytes, the IGF-1 receptor colocalized with caveolin 3 in a T-tubule-like structure close to the nucleus. We determined that CREB, but not NFkB and NFAT, was involved in the protective action of IGF-1.
Angiotensin-(1-9) (Ang-(1-9)) is a small peptide produced by the renin-angiotensin-aldosterone system (RAAS) which comes from the hydrolysis of angiotensin I, through the angiotensin converting enzyme type II (ACE II). Despite it was initially believed that its function was merely due to its conversion to Angiotensin II (Ang II), nowadays it is known that Ang-(1-9) has a physiological activity, through the interaction with the angiotensin type 2 receptor (AT2R). In some recent in vitro and in vivo studies, we have demostrated that Ang-(1-9) can prevent the cardiac hypertrophic phenotype induced by different stimuli, such as the treatment with norepinephrine (NE), Ang II and IGF-1. In these studies the effects of Ang-(1-9) were mediated by its union to the AT2R.
For more information on IGF-1 and angiotensin-(1-9), please read:
According to the World Health Organization (WHO) the leading cause of deaths in 2008 due to non communicable diseases was cardiovascular diseases (CVDs) (17 million deaths). In Chile, CVDs account for 30% of all death, followed by cancers (23%), respiratory diseases (6%) and diabetes (4%).
Our lab investigates the mechanisms involved in the genesis and development of CVDs, as well as, the application of these findings to the treatment of patients with several CVDs, such as: heart failure, hypertension, arrhythmia, myocardial infarction, pulmonary hypertension, diabetic cardiomyopathy, atherosclerosis, stenosis, and cardiac hypertrophy.
The main research line in our laboratory are:
Autophagy in the cardiovascular system
Stress, aging and diverse diseases are associated with the development of cardiac hypertrophy. Hypertrophy development and its reversal (atrophy) are achieved through changes affecting the dynamic balance between protein synthesis and proteolysis in cardiac myocytes, which in turn establish contractile and metabolic properties of the heart. There are two major intracellular proteolytic pathways in the cells: the lysosomal pathway and the ubiquitin-proteasome pathway. Whereas the lysosomal pathway plays an important role in the degradation of long lived bulk proteins, particularly membrane-bound proteins and organelles, the ubiquitin-proteasome pathway primarily participates in the degradation of cytosolic proteins.
Lysosomal pathways of protein degradation promote or antagonize disease pathogenesis in the cardiovascular system. The intricate cascade of events leading to cargo sequestration and delivery to lysosomes that contributes to the maintenance of cellular homeostasis, quality control, defense against intra- and extracellular insults, and preservation of the cellular energetic balance is known as macroautophagy. Together with chaperone-mediated autophagy (CMA), these two represent the best studied autophagic entities in our lab (Figure 1). Materials degraded by macroautophagy are used by anabolic reactions in order to maintain energy levels and to provide macromolecules for the synthesis of nucleic acids, proteins or organelles, thereby ensuring cell metabolism, homeostasis and survival. Despite this vital role, macroautophagy also contributes to cell death when it is executed excessively or inefficiently, as occurs during tissue and organ development, or pathologic states. For several years, macroautophagy has been known to exist in the heart and in the arteries. Macroautophagy in the heart and in the vasculature can confer both adaptive and maladaptive actions, depending on the context. Currently, many studies are underway to tease apart "good" from "bad" macroautophagy and to define underlying mechanisms.