Bindoff, L. A. | Search bioRxiv

bioRxiv2021

Distinct mitochondrial remodeling during early cardiomyocyte development in a human-based stem cell model

Given the considerable interest in using stem cells for modelling and treating disease, it is essential to understand what regulates self-renewal and differentiation. Remodeling of mitochondria and metabolism, with the shift from glycolysis to oxidative phosphorylation (OXPHOS), play a fundamental role in maintaining pluripotency and stem cell fate. It has been suggested that metabolic switch from glycolysis to OXPHOS is germ-layer specific as during early ectoderm commitment, glycolysis remains active while during the transition to mesoderm and endoderm lineages, it is downregulated. How mitochondria adapt during these metabolic changes and whether mitochondria remodeling is tissue specific remains unclear. Here we address the question of mitochondrial adaption by examining the differentiation of human pluripotent stem cells to cardiac progenitors and further to functional cardiomyocytes. Contrary to recent findings in neuronal differentiation, we found that mitochondrial content decreases continuously during mesoderm differentiation, despite clear mitochondrial remodeling giving increased mitochondrial activity and higher levels of ATP-linked respiration. Thus, our work both highlights similarities in mitochondrial remodeling during the transition from pluripotent to multipotent state in ectodermal and mesodermal lineages, while at the same time demonstrating cell-lineage-specific adaptions upon further differentiation. Our results improve understanding of how mitochondria remodeling and the metabolism interact during differentiation and show that it is erroneous to assume that increased OXPHOS activity during differentiation requires a simultaneous expansion of mitochondrial content. Summary statementWe found that mitochondrial content decreases continuously during mesoderm differentiation, despite clear mitochondrial remodeling giving increased mitochondrial activity and higher levels of ATP-linked respiration during mesoderm differentiation.

cell biology↗

bioRxiv2020

Stem cell derived astrocytes with POLG mutations and mitochondrial dysfunction including abnormal NAD+ metabolism is toxic for neurons

The inability to reliably replicate mitochondrial DNA (mtDNA) by mitochondrial DNA polymerase gamma (POLG) leads to a subset of common mitochondrial diseases associated with neuronal death and depletion of neuronal mtDNA. Defining disease mechanisms remains difficult due to the limited access to human tissue. Astrocytes are highly abundant in the brain, playing a crucial role in the support and modulation of neuronal function. Astrocytes also respond to insults affecting the brain. Following damage to the center neural system, which can be hypoxia, inflammation or neurodegeneration, astrocytes become activated and lose their supportive role and gain toxic functions that induce rapid death of neurons and oligodendrocytes. The role of astrocyte reactivation and the consequences this has for neuronal homeostasis in mitochondrial diseases has not been explored. Here, using patient cells carrying POLG mutations, we generated iPSCs and then differentiated into astrocytes. We demonstrated that POLG-astrocytes exhibited both mitochondrial dysfunctions, including loss of mitochondrial membrane potential, energy failure, complex I and IV defects, disturbed NAD+/NADH metabolism, and mtDNA depletion. Further, POLG derived astrocytes presented an A1-like reactive phenotype with increased proliferation, invasion, upregulation of pathways involved in response to stimulus, immune system process, cell proliferation and cell killing. Under direct and indirect co-culture with neurons, POLG-astrocytes exhibited a toxic effect leading to the death of neurons. Our findings demonstrate that mitochondrial dysfunction caused by POLG mutations leads not only to intrinsic defects in energy metabolism affecting both neurons and astrocytes, but also to neurotoxic damage driven by astrocytes. Our studies provide a robust astroglia-neuronal interaction model for future investigation of mitochondrial involvement in neurogenesis and neurodegenerative diseases. Highlights{blacksquare} Patient-specific astrocytes harbouring a POLG mutation showed lower mitochondrial membrane potential and mtDNA depletion. {blacksquare}POLG-astrocytes generated elevated L-lactate as the end glycolytic product. {blacksquare}Patient-specific astrocytes with POLG mutations exhibited mitochondrial respiratory chain disruption accompanied with abnormal UCP2/SirT1/SirT3 mediated NAD+ metabolism. {blacksquare}Suppressed complex I and IV-driven respiration contributed to the pathological mechanisms in POLG-related disease. {blacksquare}POLG-astrocytes exhibit A1-reactive phenotype and neurotoxic potential. Graphic abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=166 SRC="FIGDIR/small/423652v1_ufig1.gif" ALT="Figure 1"> View larger version (61K): org.highwire.dtl.DTLVardef@18995fdorg.highwire.dtl.DTLVardef@1d615d4org.highwire.dtl.DTLVardef@334aa8org.highwire.dtl.DTLVardef@16a84ba_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗