OCIAD1 regulates early mesodermal progenitor specification in human embryonic stem cells by altering mitochondrial activity

Abstract

Differentiation from pluripotent cells entails specification of cell intermediates with progressively limited potency. Understanding the molecular mechanisms that specify these intermediates can aid their expansion for therapeutic application and drug testing. In this thesis, we show that human Ovarian Carcinoma Immuno-reactive Antigen Domain containing 1 (OCIAD1), is expressed in human embryonic stem cells (hESCs) and cardiovascular lineages. OCIAD1 depletion by CRISPR/Cas9-mediated knockout promotes hESC differentiation to early mesodermal progenitors (EMPs). Conversely, OCIAD1 overexpression in transgenic hESC lines reduced differentiation to EMPs. OCIAD1 localizes to endosomes and mitochondria. In hESCs, it predominantly resides in the mitochondria. Cellular processes such as endocytosis and mitochondrial oxidative phosphorylation regulate stem cell differentiation but their contribution to specification of mesodermal lineages is not well understood. We show that OCIAD1 interacts with electron transport chain complex members and reduces oxidative phosphorylation activity, thus keeping cells undifferentiated. In the absence of OCIAD1, Complex I activity increases, resulting in increased oxidative phosphorylation and reduced dependence on glycolysis, thus promoting hESC differentiation. Lysophosphatidic acid, a small molecule inducer of OCIAD1, can regulate EMP differentiation in wild type hESCs, phenocopies the genetic overexpression and rescues the depletion phenotype. Thus, OCIAD1 expression levels affect cell fate choices by impacting mitochondrial activity. Genetic overexpression of OCIAD1 leads to carcinoma development in human. We provide a non-genetic reversible tool to modulate OCIAD1 and hence mesodermal precursor generation. Generation of functional cells for stem cell-based cell therapies targeted at curing several severe diseases is a major endeavor of regenerative medicine. The current focus is on harnessing the developmental function of key pluripotency regulators for the development of lineage-restricted progenitor cell lines. However, genetic manipulations and the time required for generating desired cell types pose serious limitations. Non-genetic, reversible technologies that could speed up the development of functional cell therapies and reduce costs are an urgent requirement. Our interest is in understanding cell fate specification during development of the blood, vascular and cardiac lineages from mesoderm. Improved understanding of mechanisms that specify mesoderm lineage precursors from stem cells will contribute significantly to our ability to manipulate and regulate the process for cell-based therapies.