Sex is increasingly emerging as determinant of right ventricular (RV) adaptation to abnormal loading conditions. It is unknown, however, whether sex-related differences already occur in childhood. Therefore, this study aimed to assess sex differences in a juvenile model of early RV pressure load by pulmonary artery banding (PAB) during transition from pre- to post-puberty. 3-weeks old rat pups (n=57, 30-45g) were subjected to PAB or sham surgery. Animals were sacrificed either before or after puberty (4 and 8 weeks post-surgery, respectively). Male PAB rats demonstrated failure to thrive already after 4 weeks, whereas females did not. After 8 weeks, female PAB rats showed less clinical symptoms of RV failure than male PAB rats. RV pressure-volume analysis demonstrated increased end-systolic elastance after 4 weeks in females only, and a trend toward preserved end-diastolic elastance in female PAB rats compared to males (p=0.055). Histology showed significantly less RV myocardial fibrosis in female compared to male PAB rats 8 weeks after surgery. Myosin heavy chain 7/6 ratio switch and calcineurin signaling were less pronounced in female PAB rats, compared to males. In this juvenile rat model of RV pressure load, female rats appeared to be less prone to clinical heart failure, compared to males. This was driven by increased RV contractility before puberty, and better preservation of diastolic function with less RV myocardial fibrosis after puberty. These findings show that RV adaptation to increased loading differs between sexes already before the introduction of pubertal hormones.
Aims Research on the pathophysiology of right ventricular (RV) failure has, in spite of the associated high mortality and morbidity, lagged behind compared to the left ventricle (LV). Previous work from our lab revealed that the embryonic basic helix-loop-helix transcription factor heart and neural crest derivatives expressed-2 (Hand2) is re-expressed in the adult heart and activates a ‘fetal gene program’ contributing to pathological cardiac remodeling under conditions of LV pressure overload. As such, ablation of cardiac expression of Hand2 conferred protection to cardiac stress and abrogated the maladaptive effects that were observed upon increased expression levels. In this study, we aimed to understand the contribution of Hand2 to RV remodeling in response to pressure overload induced by pulmonary artery banding (PAB). Methods and Results In the present study, Hand2F/F and MCM- Hand2F/F mice were treated with tamoxifen (control and knockout, respectively) and subjected to six weeks of RV pressure overload induced by PAB. Echocardiographic- and MRI-derived hemodynamic parameters as well as molecular remodeling were assessed for all experimental groups and compared to sham-operated controls. Six weeks after PAB, levels of Hand2 expression increased in the control banded animals but, as expected, remained absent in the knockout hearts. Despite the dramatic differences in Hand2 expression, pressure overload resulted in impaired cardiac function independently of the genotype. In fact, Hand2 depletion seems to sensitize the RV to pressure overload as these mice develop more hypertrophy and more severe cardiac dysfunction. Higher expression levels of HAND2 were also observed in RV samples of human hearts from patients with pulmonary hypertension. In turn, the LV of RV-pressure overloaded hearts was also dramatically affected as reflected by changes in shape, decreased LV mass and impaired cardiac function. RNA sequencing revealed a distinct set of genes that are dysregulated in the pressure-overloaded RV, compared to the previously described pressure-overloaded LV. Conclusions Cardiac-specific depletion of Hand2 is associated with severe cardiac dysfunction in conditions of RV pressure overload. While inhibiting Hand2 expression can prevent cardiac dysfunction in conditions of LV pressure overload, the same does not hold true for conditions of RV pressure overload. This study highlights the need to better understand the molecular mechanisms driving pathological remodeling of the RV in contrast to the LV, in order to better diagnose and treat patients with RV or LV failure. Translational Perspective RV failure associated with pulmonary hypertension reduces long-term survival rate to 55% within 3 years, suggesting that 3 years after diagnosis almost half of the patients will die. To revert these numbers an adequate RV-specific and, therefore, more efficient treatment is needed. Our work suggests that current therapies and potential mechanisms underlying LV failure may not be suitable for RV failure. While Hand2 deletion is favorable in LV response to stress, it is particularly detrimental in the RV under similar conditions, and thus, highlighting potential severe consequences of not differentiating therapeutic targets or treatment for RV or LV failure.
Introduction Heart and neural crest derivatives expressed-2 (Hand2) has been identified as an important embryonic basic helix-loop-helix-transcription factor, with different functions in the development of the first and second heart field, from which the left and right ventricle originate, respectively. Our previous work revealed that Hand2, under conditions of left ventricular (LV) pressure overload, is re-expressed in the adult heart and activates a “fetal gene” program contributing to pathological cardiac remodeling. Ablation of cardiac expression of Hand2 resulted in protection to cardiac stress and attenuated maladaptive remodeling. Purpose In this study, we aimed at unraveling the role of Hand2 during cardiac remodeling in response to right ventricular (RV) pressure overload induced by pulmonary artery banding (PAB). Methods Hand2F/F and MCM− Hand2F/F mice were treated with tamoxifen (control and knockout, respectively) and subjected to six weeks of RV pressure overload induced by PAB. Echocardiographic and MRI derived hemodynamic parameters, and molecular remodelling were assessed for experimental groups and compared to sham-operated controls (Fig. 1a). RNA sequencing and gene ontology enrichment analysis were performed to compare the dysregulated genes between the pressure overloaded RV of the control and Hand2 knockout mice. Results After six weeks of increased pressure load (Fig. 1b), levels of Hand2 increased in the control banded animals but, as expected, remained absent in the knockout hearts (Fig. 1c). In contrast to the what was previously observed for the pressure overloaded LV, in the pressure loaded RV, Hand2 depletion resulted in more severe remodelling and dysfunction as reflected by increased hypertrophic growth, increased RV end-diastolic and end-systolic volumes as well as decreased RV ejection fraction (Fig. 1d–g). In addition, RNA sequencing revealed a distinct set of genes that are dysregulated in the pressure-overloaded RV, compared to the previously described pressure-overloaded LV. These include components of the extracellular matrix structure, collagen assembly and organization and several types of collagens. Genes associated with inflammation response, adhesion and muscle organization were also affected in the RV of the Hand2 KO mice (Fig. 1h). Figure 1 Conclusion Cardiac-specific depletion of Hand2 is associated with severe cardiac dysfunction in conditions of RV pressure overload. While inhibiting Hand2 expression can prevent cardiac dysfunction in conditions of LV pressure overload, the same does not hold true for conditions of RV pressure overload. This study highlights the need to better understand the molecular mechanisms driving pathological remodelling of the RV, in contrast to the LV, in order to better diagnose and treat patients with RV or LV failure.
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