A Dual Role of the GTPase Rac in Cardiac Differentiation of Stem Cells

Abstract

The function of the GTPase Rac1, a molecular switch transducing intracellular signals from growth factors, in differentiation of a specific cell type during early embryogenesis has not been investigated. To address the question, we used embryonic stem (ES) cells differentiated into cardiomyocytes, a model that faithfully recapitulates early stages of cardiogenesis. Overexpression in ES cells of a constitutively active Rac (RacV12) but not of an active mutant (RacL61D38), which does not activate the NADPH oxydase generating ROS, prevented MEF2C expression and severely compromised cardiac cell differentiation. This resulted in poor expression of ventricular myosin light chain 2 (MLC2v) and its lack of insertion into sarcomeres. Thus ES-derived cardiomyocytes featured impaired myofibrillogenesis and contractility. Overexpression of MEF2C or addition of catalase in the culture medium rescued the phenotype of racV12 cells. In contrast, RacV12 specifically expressed in ES-derived ventricular cells improved the propensity of cardioblasts to differentiate into beating cardiomyocytes. This was attributed to both a facilitation of myofibrillogenesis and a prolongation in their proliferation. The dominant negative mutant RacN17 early or lately expressed in ES-derived cells prevented myofibrillogenesis and in turn beating of cardiomyocytes. We thus suggest a stage-dependent function of the GTPase during early embryogenesis.

Redox Modifier Genes and Pathways in Amyotrophic Lateral Sclerosis

“…In this context, it is also important to point out that the regulation of ROS production by Rac1 is important for many cellular processes that are involved in signal transduction (129), actin cytoskeletal rearrangements (71,87,102), cell migration (143), cell proliferation (66,99,108,143), and cell differentiation (113). Given that many of these pathways also involve activation and recruitment of Rac1 to specific membrane domains, it is also possible that SOD1=Rac1 interactions may influence other cellular aspects of disease progression in ALS.…”

The NADPH Oxidase NOX4 Drives Cardiac Differentiation: Role in Regulating Cardiac Transcription Factors and MAP Kinase Activation

“…This led us to postulate that low doses of ROS are not detrimental but instead elicit dose-dependent biological responses. Indeed, excessive ROS levels repress the expression of several cardiac genes (Morel and Barouki, 1999;Puceat et al, 2003). For instance, Puceat et al (2003) reported that a daily treatment of EBs with H 2 O 2 prevented the beating activity in differentiating EBs.…”

“…Indeed, excessive ROS levels repress the expression of several cardiac genes (Morel and Barouki, 1999;Puceat et al, 2003). For instance, Puceat et al (2003) reported that a daily treatment of EBs with H 2 O 2 prevented the beating activity in differentiating EBs. This is consistent with our observation that NOX4 overexpression in ESC leads to apoptosis (unpublished data).…”

Cardiac Repair by Embryonic Stem-Derived Cells

“…Similarly, overexpression of TBX5 (Fijnvandraat et al 2003a) and opioid peptide (Ventura and Maioli 2000) enhanced cardiomyogenic differentiation in embryonic carcinoma cells. Conversely, loss of beta-1 integrin (Fassler et al 1996) or alternatively overexpression of Rac-1 (Puceat et al 2003) decreased the levels of cardiomyogenesis in differentiating ES cells. Thus a large number of cytokines, inorganic molecules, and genes have been identified that influenced the ability of ES cells to generate cardiomyocytes.…”