Mitochondria and stem cell function: from somatic cells to iPSC-based disease modeling

Abstract

Homeostasis of the hematopoietic stem/progenitor cell pool relies on a finely tuned balance between self-renewal, differentiation and proliferation. Recent work has revealed the importance of mitochondria during stem cell differentiation; however, it remains unclear whether mitochondrial content/function affects human hematopoietic stem versus progenitor function. We sorted cord blood-derived CD34+ cells on the basis of mitochondrial mass and examined their homeostasis and clonogenic potential in vitro and hematopoietic repopulation potential in vivo. CD34+ cells with high mitochondrial mass contained and expressed 2-fold high ATP levels and mitochondrial-specific genes than cells with low mitochondrial mass, however, HIF-1α and MEIS1 were high in the CD34+ cells with low mitochondria. We found that CD34+ cells with low mitochondrial content were enriched for hematopoietic stem cell function as demonstrated by significantly higher hematopoietic reconstitution potential in immunodeficient mice. By contrast, CD34+ cells with high mitochondrial content were enriched for hematopoietic progenitor function with high in vitro clonogenic capacity.

Coenzyme Q10 (CoQ10) plays a critical role in mitochondria as an electron carrier within the electron transport chain (ETC) and is an essential antioxidant. Mutations in genes responsible for CoQ10 biosynthesis (COQ genes) cause primary CoQ10 deficiency, a rare and heterogeneous mitochondrial disorder with no clear genotype-phenotype association, mainly affecting tissues with high energy demand including brain and skeletal muscle (SkM). A four-year-old girl was identified with a heterozygous mutation (c.483G>C; E161D) in COQ4, associated with a reduction in [CoQ10], CoQ10 biosynthesis and ETC activity affecting complexes I/II+III. Bona fide induced pluripotent stem cell (iPSC) lines carrying the COQ4 mutation (CQ4-iPSCs) were generated, characterized and genetically corrected using CRISPR/Cas9 genome-editing (CQ4ed-iPSCs). Comprehensive differentiation and metabolic analysis of control-iPSCs, CQ4-iPSCs and CQ4ed-iPSCs faithfully reproduced the disease phenotype. Accordingly, the COQ4 mutation in iPSCs was associated with CoQ10 deficiency, metabolic dysfunction and impaired differentiation into SkM. Remarkably, differentiation of CQ4-iPSCs into dopaminergic or motor neurons was unaffected. This study offers an unprecedented iPSC model recapitulating CoQ10 deficiency-associated functional and metabolic phenotypes caused by COQ4 mutation.