BMPER regulates cardiomyocyte size and vessel density in vivo

Background: BMPER, an orthologue of Drosophila melanogaster crossveinless-2, is a secreted factor that regulates BMP activity in endothelial cell precursors and during early cardiomyocyte differentiation. Although previously described in the heart, the role of Bmper in cardiac development and function remained unknown. Methods: BMPER deficient hearts were phenotyped histologically and functionally using echocardiography and Doppler analysis. Since BMPER -/- mice die perinatally, BMPER +/- mice were then challenged to pressure overload induced cardiac hypertrophy and hind limb ischemia to determine changes in angiogensis and regulation of cardiomyocyte size. Results: We identified for the first time the cardiac phenotype associated with BMPER haploinsufficiency. BMPER mRNA and protein are present in the heart during cardiac development through at least E14.5 but is lost by E18.5. BMPER +/- ventricles are thinner and less compact than sibling wild-type hearts. In the adult, BMPER +/- hearts present with decreased anterior and posterior wall thickness, decreased cardiomyocyte size, and an increase in cardiac vessel density. Despite these changes, BMPER +/- mice respond to pressure overload-induced cardiac hypertrophy challenge largely to the same extent as wild-type mice. Conclusion: BMPER appears to play a role in regulating both vessel density and cardiac development in vivo; however, BMPER haploinsufficiency does not result in marked effects on cardiac function or adaptation to pressure overload hypertrophy. Unpaired, two-condition experiment, wild-type vs BMPER+/- adult hearts. Biological replicates: 4 per condition.研究背景：BMPER是果蝇（Drosophila melanogaster）crossveinless-2的直系同源蛋白，属于分泌因子，可在内皮细胞前体及早期心肌细胞分化过程中调控骨形态发生蛋白（Bone Morphogenetic Protein, BMP）的活性。尽管此前已有研究在心脏中报道过BMPER的存在，但该因子在心脏发育与功能中的具体作用仍未明确。实验方法：通过组织学检测、超声心动图与多普勒分析，对BMPER缺陷型心脏进行表型鉴定。由于BMPER全敲除（BMPER -/-）小鼠会在围产期死亡，本研究后续采用BMPER杂合敲除（BMPER +/-）小鼠，通过构建压力负荷诱导的心肌肥厚模型与后肢缺血模型，探究其血管生成变化与心肌细胞尺寸的调控情况。实验结果：本研究首次明确了与BMPER单倍剂量不足相关的心脏表型。在心脏发育进程中，直至胚胎期14.5天（E14.5），小鼠心脏中均可检测到BMPER的mRNA与蛋白表达，但至胚胎期18.5天（E18.5）时该表达消失。与同窝野生型小鼠心脏相比，BMPER +/-小鼠的心室壁更薄、结构更疏松。成年BMPER +/-小鼠心脏表现为前后壁厚度降低、心肌细胞尺寸减小，同时心脏血管密度升高。尽管存在上述表型变化，BMPER +/-小鼠在接受压力负荷诱导的心肌肥厚造模后，其心脏的响应程度与野生型小鼠基本一致。研究结论：BMPER在体内可同时调控血管密度与心脏发育；但BMPER单倍剂量不足并不会对心脏功能或其对压力负荷诱导心肌肥厚的适应能力产生显著影响。本研究采用非配对双组实验设计，对比成年野生型与BMPER +/-小鼠的心脏样本，每组设置4个生物学重复。