Mitofusins 1 and 2 are essential for postnatal metabolic remodeling in heart.
BACKGROUND
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
The objective of this study was to determine the significance of mitofusins during early postnatal cardiac development.


RESULTS
We genetically inactivated Mfn-1 and Mfn-2 in midgestational 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. At this time point, DKO mice have developed cardiomyopathy. This leads to a rapid decline in survival and all DKO mice die before 16 days of age. Gene expression analysis of DKO hearts shows that mitochondria biogenesis genes are downregulated, the mitochondrial DNA is reduced, and mitochondrially encoded transcripts and proteins are also reduced. 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.
Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA, USA.
Kyriakos N
KN
Papanicolaou
Ryosuke
R
Kikuchi
Gladys A
GA
Ngoh
Kimberly A
KA
Coughlan
Isabel
I
Dominguez
William C
WC
Stanley
Kenneth
K
Walsh
D000818:Animals; D000831:Animals, Newborn; D004272:DNA, Mitochondrial / Q000235:genetics / Q000378:metabolism; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D006321:Heart / Q000196:embryology* / Q000254:growth & development* / Q000502:physiology; D006333:Heart Failure / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008854:Microscopy, Electron; D008928:Mitochondria / Q000473:pathology / Q000502:physiology / Q000648:ultrastructure; D009206:Myocardium / Q000473:pathology; D032383:Myocytes, Cardiac / Q000473:pathology / Q000502:physiology* / Q000648:ultrastructure; D009210:Myofibrils / Q000473:pathology / Q000502:physiology / Q000648:ultrastructure; D015996:Survival Rate
D004272:DNA, Mitochondrial; D020558:GTP Phosphohydrolases; C488750:Mfn1 protein, mouse; C488751:Mfn2 protein, mouse