DUSP5 expression in left ventricular cardiomyocytes of young hearts regulates thyroid hormone (T3)-induced proliferative ERK1/2 signaling

Abstract

Cardiomyocytes of newborn mice proliferate after injury or exposure to growth factors. However, these responses are diminished after postnatal day-6 (P6), representing a barrier to building new cardiac muscle in adults. We have previously shown that exogenous thyroid hormone (T3) stimulates cardiomyocyte proliferation in P2 cardiomyocytes, by activating insulin-like growth factor-1 receptor (IGF-1R)-mediated ERK1/2 signaling. But whether exogenous T3 functions as a mitogen in post-P6 murine hearts is not known. Here, we show that exogenous T3 increases the cardiomyocyte endowment of P8 hearts, but the proliferative response is confined to cardiomyocytes of the left ventricular (LV) apex. Exogenous T3 stimulates proliferative ERK1/2 signaling in apical cardiomyocytes, but not in those of the LV base, which is inhibited by expression of the nuclear phospho-ERK1/2-specific dual-specificity phosphatase, DUSP5. Developmentally, between P7 and P14, DUSP5 expression increases in the myocardium from the LV base to its apex; after this period, it is uniformly expressed throughout the LV. In young adult hearts, exogenous T3 increases cardiomyocyte numbers after DUSP5 depletion, which might be useful for eliciting cardiac regeneration.

Thyroid hormone plus dual-specificity phosphatase-5 siRNA increases the number of cardiac muscle cells and improves left ventricular contractile function in chronic doxorubicin-injured hearts

“…C57BL/6 wild type (Jackson Laboratory, 000664) male and female mice were used for breeding and for the studies reported here. Animal husbandry was performed as described 10 - 11 . For cardiomyocyte lineage tracing studies, we used Rosa26fs-Confetti[B6.129P2-Gt(ROSA)26Sortm1(CAG-Brainbow2.1)Cle/J, Jackson Laboratory, 017492] and Myh6-MerCreMer [B6.FVB(129)-A1cfTg(Myh6-cre/Esr1*)1Jmk/J, Jackson Laboratory, 005657] mice.…”

“…Transthoracic echocardiography was performed as described 11 . Briefly, echocardiography was performed under light isoflurane anesthesia on either DUSP5 siRNA or scrambled siRNA ± T3 treated mice using the Vevo 3100 imaging platform (VisualSonics Inc.) with a MX550D linear array transducer (axial resolution: 40 µm) and images were analyzed using Vevo Lab Desktop Software.…”

“…The protocol for cardiomyocyte number determination was as described previously 10 - 11 . Briefly, heparin (100-200 µl, 1000 USP units/ml) was injected intraperitoneally eight minutes prior to harvesting.…”

“…Immunofluorescence was performed as described earlier 10 - 11 . Briefly, cardiomyocytes were isolated as described above and fixed in Cytofix (BD Biosciences, 554655) for 5 min.…”

“…JNK2α2 activation phosphorylates c-Jun, a component of the activator protein 1 (AP-1) early response transcription factor, resulting in enhanced IGF-1 expression and activation of proliferative ERK1/2 signaling. In young adult hearts (about 5 weeks old), however, T3 increases IGF-1 expression and IGF-1 receptor phosphorylation, but proliferative ERK1/2 signaling in cardiomyocytes is diminished and cardiomyocyte proliferation does not occur 11 . The mechanism for this diminished ERK1/2 response involves the developmentally delayed expression in ventricular cardiomyocytes of the nuclear ERK1/2-specific dual specificity phosphatase, DUSP5, which starts at postnatal day-7 (P7) 11 .…”