Role of CD133 molecule in WNT response and renal repair

Renal repair after injury is dependent on clonal expansion of proliferation competent cells. In the human kidney, the expression of CD133+ characterizes a population of resident scattered cells with resistance to damage and ability to proliferate. However, the biological function of the CD133 molecule is unknown. We found by RNA sequencing that cells undergoing cisplatin damage lost the CD133 signature and acquired metanephric mesenchymal and regenerative genes such as SNAIL1, KLF4, SOX9 and WNT3. CD133 was reacquired in the recovery phase. Lack of CD133 was specifically correlated with deregulation of the Wnt signalling and E-cadherin pathway and, functionally, limited cell proliferation after injury. By immunoprecipitation, CD133 appeared to form a complex with E-cadherin and β-catenin. In parallel, CD133-Kd cells showed lower β-catenin levels in basal condition and after Wnt pathway activation and reduced TCF/LEF promoter activation in respect to CD133+ cells. Finally, the lack of CD133 impaired generation of nephrospheres while favored senescence. These data indicate that CD133 may act as a permissive factor for beta-catenin signalling, preventing its degradation in the cytoplasm. Therefore, CD133 itself appears to play a functional role in renal tubular repair trough maintenance of proliferative response and control of senescence.

损伤后的肾脏修复依赖于具备增殖能力的细胞的克隆扩增。在人体肾脏中，CD133阳性（CD133+）细胞群的特征为散在分布的驻留细胞，这类细胞对损伤具有抵抗力且具备增殖能力。然而，CD133分子的生物学功能目前尚不明确。我们通过RNA测序（RNA sequencing）发现，经顺铂（cisplatin）处理发生损伤的细胞会丢失CD133表达特征，并获得后肾间充质（metanephric mesenchymal）及再生相关基因，例如SNAIL1、KLF4、SOX9以及WNT3。在损伤修复阶段，细胞会重新表达CD133。CD133的缺失特异性地与Wnt信号通路及上皮钙粘蛋白（E-cadherin）通路的失调相关；在功能层面，CD133缺失会限制损伤后的细胞增殖能力。通过免疫共沉淀（immunoprecipitation）实验，我们发现CD133可与上皮钙粘蛋白及β-连环蛋白（β-catenin）形成复合物。与此同时，与CD133+细胞相比，CD133敲低（CD133-Kd）细胞在基础状态及Wnt通路激活后的β-连环蛋白水平更低，且TCF/LEF启动子的激活活性也有所降低。最后，CD133的缺失会损害肾球状体（nephrospheres）的生成，同时促进细胞衰老。上述研究结果表明，CD133可作为β-连环蛋白信号通路的许可因子，阻止其在细胞质中被降解。因此，CD133本身似乎通过维持增殖反应及调控细胞衰老，在肾小管修复过程中发挥功能性作用。