Mitofusins 1 and 2 are Essential for Postnatal Metabolic Remodeling in Heart
Rationale: At birth, there is a switch from placental to pulmonary circulation and the heart commences its aerobic metabolism. In cardiac myocytes, this transition is marked by increased mitochondrial biogenesis and remodeling of the intracellular architecture. The mechanisms governing the formation of new mitochondria and their expansion within myocytes remain largely unknown. Mitofusins (Mfn-1 and Mfn-2) are known regulators of mitochondrial networks but their role during perinatal maturation of the heart has yet to be examined.
Objective: Determine the significance of mitofusins, during early postnatal cardiac development.
Methods and Results: We genetically inactivated Mfn-1 and Mfn-2 in mid-gestational and postnatal cardiac myocytes using a loxP/Myh6-cre approach. At birth, cardiac morphology and function of double-knockout (DKO) mice are normal. At that time, DKO mitochondria increase in numbers, appear to be spherical and heterogeneous in size but exhibit normal electron-density. By postnatal day 7, the mitochondrial numbers in DKO myocytes remain abnormally expanded and many lose matrix components and membrane organization. In this context, DKO mice develop dilated cardiomyopathy (DCM). This leads to a rapid decline in survival and all DKO mice perish before 16 days of age. Gene expression analysis of DKO hearts shows that mitochondria biogenesis genes are down regulated, the mitochondrial DNA is reduced and so are mitochondrially-encoded transcripts and proteins. Furthermore, mitochondrial turnover pathways are dysregulated.
Conclusions: Our findings establish that Mfn-1 and Mfn-2 are essential in mediating mitochondrial remodeling during postnatal cardiac development, a time of dramatic transitions in the bioenergetics and growth of the heart.
- Received May 21, 2012.
- Accepted August 17, 2012.
- Copyright © 2012, American Heart Association