Cauquil, M. | Search bioRxiv

bioRxiv2022

Crest maturation at the cardiomyocyte surface contributes to a new late postnatal development stage that controls the diastolic function of the adult heart

RATIONALEIn addition to its typical rod-shape, the mammalian adult cardiomyocyte (CM) harbors a unique lateral membrane surface architecture with periodic crests, relying on the presence of subsarcolemmal mitochondria (SSM) the role of which is still unknown. OBJECTIVETo investigate the development and functional role of CM crests during the postnatal period. METHODS AND RESULTSElectron/confocal microscopy and western-blot of left ventricular tissues from rat hearts indicated a late CM surface crest maturation, between postnatal day 20 (P20) and P60, as shown by substantial SSM swelling and increased claudin-5 cell surface expression. The P20-P60 postnatal stage also correlates with an ultimate maturation of the T-Tubules and the intercalated disk. At the cellular level, we identified an atypical CM hypertrophy characterized by an increase in long- and short-axes without myofibril addition and with sarcomere lateral stretching, indicative of lateral stretch-based CM hypertrophy. We confirmed the P20-P60 hypertrophy at the organ level by echocardiography but also demonstrated a transcriptomic program after P20 targeting all the cardiac cell populations. At the functional level, using Doppler echocardiography, we found that the P20-P60 period is specifically dedicated to the improvement of relaxation. Mechanistically, using CM-specific knock-out mice, we identified ephrin-B1 as a determinant of CM crest maturation after P20 controlling lateral CM stretch-hypertrophy and relaxation. Interestingly, while young adult Efnb1CMspe-/- mice essentially show a relaxation impairment with exercise intolerance, they progressively switch toward heart failure with 100% KO mice dying after 13 months. CONCLUSIONSThis study highlights a new late P20-P60 postnatal developmental stage of the heart in rodents during which the CM surface crests mature through an ephrin-B1-dependant mechanism and regulate the diastolic function. Moreover, we demonstrate for the first time that the CM crest architecture is cardioprotective.

cell biology↗

bioRxiv2019

Ephrin-B1 blocks adult cardiomyocyte proliferation and heart regeneration

AimsDeciphering the innate mechanisms governing the blockade of proliferation in adult cardiomyocytes (CMs) is challenging for mammalian heart regeneration. Despite the exit of CMs from the cell cycle during the postnatal maturation period coincides with their morphological switch to a typical adult rod-shape, whether these two processes are connected is unknown. Here, we examined the role of ephrin-B1, a CM rod-shape stabilizer, in adult CM proliferation and cardiac regeneration.\n\nMethods and resultsTransgenic- or AAV9-based ephrin-B1 repression in adult mouse heart led to substantial proliferation of resident CMs and tissue regeneration to compensate for apex resection, myocardial infarction (MI) and senescence. Interestingly, in the resting state, CMs lacking ephrin-B1 did not constitutively proliferate, indicative of no major cardiac defects. However, they exhibited proliferation-competent signature, as indicated by higher mononucleated state and a dramatic decrease of miR-195 mitotic blocker, which can be mobilized under neuregulin-1 stimulation in vitro and in vivo. Mechanistically, the post-mitotic state of the adult CM relies on ephrin-B1 sequestering of inactive phospho-Yap1, the effector of the Hippo-pathway, at the lateral membrane. Hence, ephrin-B1 repression leads to phospho-Yap1 release in the cytosol but CM quiescence at resting state. Upon cardiac stresses (apectomy, MI, senescence), Yap1 could be activated and translocated to the nucleus to induce proliferation-gene expression and consequent CM proliferation\n\nConclusionsOur results identified ephrin-B1 as a new natural locker of adult CM proliferation and emphasize that targeting ephrin-B1 may prove a future promising approach in cardiac regenerative medicine for HF treatment.\n\nSignificanceThe mammalian adult heart is unable to regenerate due to the inability of cardiomyocytes (CMs) to proliferate and replace cardiac tissue lost. Exploiting CM-specific transgenic mice or AAV9-based gene therapy, this works identifies ephrin-B1, a specific rod-shape stabilizer of the adult CM, as a natural padlock of adult CM proliferation for compensatory adaptation to different cardiac stresses (apectomy, MI, senescence), thus emphasizing a new link between the adult CM morphology and their proliferation potential. Moreover, the study demonstrates proof-of-concept that targeting ephrin-B1 may be an innovative therapeutic approach for ischemic heart failure.

physiology↗