SIRT1 regulates cardiomyocyte alignment and contraction during maturation in part through deacetylation of ACTN2

Authors

• Y Fang
• W Fan
• X Xu
• S Tang
• H Huang
• AK Janoshazi
• Y Zhao
• DC Fargo
• X Li

Abstract

Cardiomyocyte elongation and alignment starting from the perinatal stage is a critical step in cardiomyocyte maturation. It is crucial for formation of the highly organized intra- and inter-cellular structures for spatially and temporally ordered contraction in adult cardiomyocytes. However, control of cardiomyocyte alignment remains elusive. Here we report that SIRT1, a highly conserved NAD+-dependent protein deacetylase, plays an unexpected role in regulating cardiomyocyte elongation/alignment during development. Deletion of SIRT1 in mice does not impair the general heart morphology, nor the expression levels of key genes involved in cardiomyocyte differentiation and contraction. Instead, SIRT1 deficiency results in reduced size and randomized distribution of sarcomeres at the inter-cellular level in the murine hearts at the perinatal stages, as revealed by 3-D imaging of myofibrils and EM analysis of the sarcomere ultrastructure. Utilizing cardiomyocytes induced from human embryonic stem cells (hESCs), we confirmed that although SIRT1 deficiency causes a two-day delay in differentiation of early cardiac progenitors from hESCs, it does not impair differentiation of cardiomyocytes from progenitors at late stages. Also in line with our observations in vivo, SIRT1 deficient induced-cardiomyocytes (iCMs) fail to elongate and align along a common axis. Functionally, SIRT1 KO iCMs exhibit higher frequency and reduced amplitude of contraction, and fail to initiate beating after replating. Mechanistically, we demonstrate that α-actinin 2 (ACTN2), a key protein constituting sarcomeric Z-lines, is a novel SIRT1 deacetylation substrate. SIRT1 interacts and deacetylates ACTN2, promoting ACTN2 binding to phosphatidylinositol 4, 5-bisphosphate (PIP2) and TITIN. Consistently, an ACTN2 deacetylation mimic (ACTN2 K181R) shows better recovery during a ACTN2-mCherry FRAP analysis, and partially rescues SIRT1 deficiency-induced defects in cardiomyocyte morphology and beating. Our study identifies the first regulatory factor that modulate cardiomyocyte alignment at the inter-cellular level during maturation and provides a novel insight into future developments of cardiac regeneration. Our study also reveals an unexpected novel cytosolic function/substrate of SIRT1 in cardiomyocytes, and suggests that therapeutic interventions with SIRT1-activating compounds might be beneficial for the treatment of human heart diseases.

Scientific Focus Area: Stem Cell Biology

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