We recently brought you news of an exciting study led by Juan Carlos Izpisua Belmonte in which his group successfully eliminated mutant mitochondrial (mt)DNA in oocytes to inhibit germline transmission of currently incurable mitochondrial diseases.
Well he’s back, and this time he brought a friend. Shoukhrat Mitalipov has teamed up with Izpisua Belmonte in a new study in Nature, in which they describe how two different reprogramming techniques can generate “healthy” mutation-corrected human pluripotent stem cells (hPSCs) from patients carrying mutant mtDNA.
It is hoped that differentiation of these mitochondrially healthy hPSCs will provide much needed cell therapies for those suffering from debilitating mitochondrial diseases.
To do this, the researchers used Sendai virus-based reprogramming to generate induced pluripotent stem cells (iPSCs), and human somatic cell nuclear transfer (SCNT) to generate pluripotent stem cells (PSCs).
- The first strategy involved the derivation of iPSC lines from fibroblasts carrying common heteroplasmic mutations (mixture of wild type and mutant mitochondrial DNA).
- The reprogramming process generated different clones with varying levels of mutant mtDNA (heteroplasmic mtDNA segregation)
- This allowed the isolation of iPSC lines which contained only wild type mtDNA, and not mutant mtDNA.
- The reprogramming process generated different clones with varying levels of mutant mtDNA (heteroplasmic mtDNA segregation)
- Next, the researchers employed human SCNT to generate PSCs from fibroblasts with a homoplasmic mutation (little or no wild type mtDNA).
- The researchers transplanted a fibroblast nuclei into a human oocyte carrying healthy mitochondria to generate hPSCs lacking any parental mutant mtDNA.
- Despite ‘unmatched’ donor mtDNA, corrected cells displayed transcriptomic profiles similar to wild type embryo-derived PSCs.
- While fibroblasts with mutant mtDNA showed impaired oxygen consumption and ATP production, those generated from genetically rescued hPSCs displayed normal metabolic function.
This suggests that both reprogramming techniques can provide a source of healthy, mutation-corrected pluripotent stem cells with a wild type metabolism which can generate replacement cells/tissues from those suffering from mitochondrial disease.
While the iPSC route appears the simpler of the two strategies, the mechanisms behind the spontaneous segregation of mitochondria during reprogramming still remains unexplained.
See the details on how these reprogramming technologies combined to great effect at Nature, July 2015.