BubR1 allelic effects drive phenotypic heterogeneity in MVA progeria syndrome [10 month old RNA-seq]

Mosaic-variegated aneuploidy (MVA) syndrome is a rare childhood disorder characterized by biallelic BUBR1, CEP57, or TRIP13 aberrations, increased chromosome missegregation, and a broad spectrum of clinical features, including various cancers, congenital defects, and progeroid pathologies. To investigate the mechanisms underlying this disorder and its phenotypic heterogeneity, we mimicked the BUBR1L1012P mutation in mice (BubR1L1002P) and combined it with two other MVA variants, BUBR1X753 and BUBR1H, generating a truncated protein and low amounts of wildtype protein, respectively. Whereas, BubR1X753/L1002P and BubR1H/X753 mice die prematurely, BubR1H/L1002P mice are viable and exhibit many MVA features, including cancer predisposition and various progeroid phenotypes, including short lifespan, dwarfism, lipodystrophy, sarcopenia, and low cardiac stress tolerance. Strikingly, although these mice had a similar reduction in total BubR1 and spectrum of MVA phenotypes as BubR1H/H mice, several progeroid pathologies were attenuated in severity, which in skeletal muscle coincided with reduced senescence-associated secretory phenotype (SASP) complexity. Additionally, mice harboring heterozygous BUBR1 MVA variants developed mild MVA pathologies later in life, with alleles conferring unique phenotypic profiles. Together, these data demonstrate that subtle BUBR1 allelic effects contribute to disease heterogeneity in both MVA patients and heterozygous carriers of MVA mutations, independent of aneuploidy rates and BUBR1 protein levels. Skeletal muscle (skM, gastrocnemius) and fat (IAT) from 8-10-month-old wildtype and progeroid BubR1 MVA mutant mice (BubR1H/L1002P and BubR1H/H) were collected and harvested from naturally aged mice, euthanized at 8-10 months of age. RNA was extracted from tissues and was used for RNA sequencing.镶嵌型可变非整倍体（Mosaic-variegated aneuploidy, MVA）综合征是一种罕见的儿童疾病，其特征为双等位基因BUBR1、CEP57或TRIP13发生畸变、染色体分离错误率升高，以及涵盖多种癌症、先天性畸形与早衰性病变的广泛临床表型谱。为探究该疾病的发病机制及其表型异质性，我们在小鼠模型中模拟了人类BUBR1L1012P突变（对应小鼠源BubR1L1002P位点突变），并联合另外两种MVA相关变异体BUBR1X753与BUBR1H，分别构建了表达截短型蛋白与低水平野生型蛋白的小鼠模型。其中，BubR1X753/L1002P与BubR1H/X753双突变小鼠会过早死亡，而BubR1H/L1002P小鼠可正常存活，并表现出多种MVA特征，包括癌症易感性与一系列早衰表型，如寿命缩短、侏儒症、脂肪营养不良、肌肉减少症以及心脏应激耐受性下降。值得注意的是，尽管此类小鼠的总BubR1蛋白水平下降幅度与MVA表型谱均与BubR1H/H纯合突变小鼠相似，但部分早衰性病变的严重程度有所减轻，其中骨骼肌病变的缓解与衰老相关分泌表型（SASP）复杂度降低存在相关性。此外，携带杂合BUBR1 MVA变异体的小鼠会在晚年出现轻度MVA病变，不同等位基因可赋予独特的表型特征。综上，本研究数据表明，细微的BUBR1等位基因效应可导致MVA患者与MVA突变杂合携带者出现疾病异质性，且该过程与非整倍体发生率及BubR1蛋白水平均无关。本研究收集了8~10月龄野生型小鼠与早衰型BubR1 MVA突变小鼠（包括BubR1H/L1002P与BubR1H/H品系）的骨骼肌（skM，即腓肠肌）与脂肪组织（内脏脂肪组织，IAT），同时采集了同期实施安乐死的8~10月龄自然衰老小鼠的对应组织。随后从组织中提取总RNA，并进行RNA测序。