Lumenal calcification and microvasculopathy in fetuin-A-deficient mice lead to multiple organ morbidity

The plasma protein fetuin-A mediates the formation of protein-mineral colloids known as calciprotein particles (CPP)–rapid clearance of these CPP by the reticuloendothelial system prevents errant mineral precipitation and therefore pathological mineralization (calcification). The mutant mouse strain D2,Ahsg-/- combines fetuin-A deficiency with the calcification-prone DBA/2 genetic background, having a particularly severe compound phenotype of microvascular and soft tissue calcification. Here we studied mechanisms leading to soft tissue calcification, organ damage and death in these mice. We analyzed mice longitudinally by echocardiography, X-ray-computed tomography, analytical electron microscopy, histology, mass spectrometry proteomics, and genome-wide microarray-based expression analyses of D2 wildtype and Ahsg-/- mice. Fetuin-A-deficient mice had calcified lesions in myocardium, lung, brown adipose tissue, reproductive organs, spleen, pancreas, kidney and the skin, associated with reduced growth, cardiac output and premature death. Importantly, early-stage calcified lesions presented in the lumen of the microvasculature suggesting precipitation of mineral containing complexes from the fluid phase of blood. Genome-wide expression analysis of calcified lesions and surrounding (not calcified) tissue, together with morphological observations, indicated that the calcification was not associated with osteochondrogenic cell differentiation, but rather with thrombosis and fibrosis. Collectively, these results demonstrate that soft tissue calcification can start by intravascular mineral deposition causing microvasculopathy, which impacts on growth, organ function and survival. Our study underscores the importance of fetuin-A and related systemic regulators of calcified matrix metabolism to prevent cardiovascular disease, especially in dysregulated mineral homeostasis.血浆蛋白胎球蛋白-A（fetuin-A）可介导被称为钙蛋白颗粒（calciprotein particles, CPP）的蛋白质-矿物胶体形成——网状内皮系统对这类钙蛋白颗粒的快速清除，可阻断异常矿物沉积，从而避免病理性矿化（钙化）。突变小鼠品系D2.Ahsg-/-同时携带胎球蛋白-A缺陷与易钙化的DBA/2遗传背景，其微血管与软组织钙化的复合表型尤为显著。本研究旨在探究该品系小鼠出现软组织钙化、器官损伤及死亡的机制。我们通过超声心动图、X射线计算机断层扫描、分析型电子显微镜、组织学、质谱蛋白质组学，以及对D2野生型与Ahsg-/-小鼠开展全基因组微阵列表达分析，对小鼠进行了纵向追踪研究。胎球蛋白-A缺陷小鼠的心肌、肺、棕色脂肪组织、生殖器官、脾脏、胰腺、肾脏及皮肤均存在钙化病灶，且伴随生长受限、心输出量降低与过早死亡。重要的是，早期钙化病灶出现在微血管管腔中，表明血液液相中含矿物复合物发生了沉积。对钙化病灶及周围（非钙化）组织的全基因组表达分析，结合形态学观察结果显示，此次钙化并非与成骨软骨细胞分化相关，而是与血栓形成及纤维化有关。综上，本研究结果证实，软组织钙化可由血管内矿物沉积引发微血管病所启动，该病变会对生长、器官功能及生存造成不良影响。本研究凸显了胎球蛋白-A及钙化基质代谢相关系统性调控因子在预防心血管疾病中的重要意义，尤其在矿稳态失调的场景下。