Reprogramming cardiac fibroblast cells to transform into beating heart
muscle

Date:
August 31, 2020
Source:
University of Tsukuba
Summary:
Researchers have clarified the roles of matrix stiffness
and mechanotransduction as well as the signaling pathways in
the transformation of cardiac fibroblasts into contractile
cardiomyocytes and show that soft substrates comparable
to native myocardium improve the efficiency of this cardiac
reprogramming. This has potential for research into biomaterials
and may lead to clinical advances in regenerative treatment for
heart failure.



FULL STORY ========================================================================== Cardiovascular disease is the leading cause of death in humans. Worldwide,
as the population ages, the burden of treating heart failure is
increasing; opportunities for heart transplantation cannot keep pace. As
adult cardiomyocytes (heart muscle cells) are terminally differentiated
and do not proliferate, regeneration may be the answer. Support cells
like fibroblasts can be directly reprogrammed in vitro, but these
induced cardiomyocytes (iCMs) are less mature than those in vivo. Now, researchers at the University of Tsukuba have identified the roles of
matrix stiffness and mechanotransduction in cardiac reprogramming,
showing that matrices with softness comparable to native myocardium
enhance the efficiency of this transformation by about 15%.


========================================================================== Mammalian myocardium is essentially incapable of regeneration following
injury.

Instead, a non-contractile fibrous scar forms to maintain structural
integrity; compensatory hypertrophy is often inadequate to prevent
eventual cardiac failure. Though cell transplantation holds potential, regeneration of damaged myocardium by direct reprogramming of cardiac fibroblasts, present in abundance, is a viable alternate strategy.

The researchers sought to investigate the signaling pathways for
cardiac reprogramming as well as the underlying mechanotransductive
processes (whereby cells convert physical stresses into electrochemical signals). They first prepared Matrigel-coated polystyrene dishes and Matrigel-based hydrogels to replicate extracellular matrices (ECM) with elasticities ranging from that of brain tissue to bone. These substrates
were plated with transgenic mouse fibroblasts which were later transduced
with four cardiac transcription factors, Gata4, Mef2c, Tbx5 and hand2
(GHMT), to generate iCMs.

"After four weeks, we found that soft substrates showed significantly
more spontaneously beating iCMs, maximally on those matching native myocardium," says senior author, Professor Masaki Ieda. "Additionally,
using innovative high-speed video microscopy and motion vector analysis,
we demonstrated increased iCM contraction/relaxation velocities on those substrates, thus illustrating their functional maturation." Further immunocytochemistry, western blot analysis, and fluorescence-activated
cell sorting analysis helped elucidate the underlying mechanisms and
signaling pathways. The researchers showed that soft ECM promotes cardiac reprogramming by inhibiting two related transcriptional co-activators,
YAP and TAZ, thus suppressing fibroblast signatures. The upstream mechanotransduction pathway was also elucidated; suppression of YAP/TAZ
was mediated by inhibition of integrins (transmembrane receptors that facilitate and signal ECM adhesion), Rho/ROCK (a kinase that modulates
cell shape and movement), and actomyosin (a contractile protein-complex).

Professor Ieda explains the implications of their results:
"Following a heart attack, the healing myocardium stiffens due to
fibrosis. Understanding how matrix softness and mechanobiology affect
cardiac reprogramming could inform clinical research. Direct reprogramming
of cardiac fibroblasts may allow replacement of non-contractile scar by functional muscle in patients recovering from myocardial infarction."

========================================================================== Story Source: Materials provided by University_of_Tsukuba. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Shota Kurotsu, Taketaro Sadahiro, Ryo Fujita, Hidenori Tani,
Hiroyuki
Yamakawa, Fumiya Tamura, Mari Isomi, Hidenori Kojima, Yu Yamada,
Yuto Abe, Yoshiko Murakata, Tatsuya Akiyama, Naoto Muraoka,
Ichiro Harada, Takeshi Suzuki, Keiichi Fukuda, Masaki Ieda. Soft
Matrix Promotes Cardiac Reprogramming via Inhibition of YAP/TAZ
and Suppression of Fibroblast Signatures. Stem Cell Reports, 2020;
DOI: 10.1016/j.stemcr.2020.07.022 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200831094728.htm

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