Table_2_Suppression of the necroptotic cell death pathways improves survival in Smn2B/− mice.DOCX

Spinal muscular atrophy (SMA) is a monogenic neuromuscular disease caused by low levels of the Survival Motor Neuron (SMN) protein. Motor neuron degeneration is the central hallmark of the disease. However, the SMN protein is ubiquitously expressed and depletion of the protein in peripheral tissues results in intrinsic disease manifestations, including muscle defects, independent of neurodegeneration. The approved SMN-restoring therapies have led to remarkable clinical improvements in SMA patients. Yet, the presence of a significant number of non-responders stresses the need for complementary therapeutic strategies targeting processes which do not rely solely on restoring SMN. Dysregulated cell death pathways are candidates for SMN-independent pathomechanisms in SMA. Receptor-interacting protein kinase 1 (RIPK1) and RIPK3 have been widely recognized as critical therapeutic targets of necroptosis, an important form of programmed cell death. In addition, Caspase-1 plays a fundamental role in inflammation and cell death. In this study, we evaluate the role of necroptosis, particularly RIPK3 and Caspase-1, in the Smn2B/− mouse model of SMA. We have generated a triple mutant (TKO), the Smn2B/−; Ripk3−/−; Casp1−/− mouse. TKO mice displayed a robust increase in survival and improved motor function compared to Smn2B/− mice. While there was no protection against motor neuron loss or neuromuscular junction pathology, larger muscle fibers were observed in TKO mice compared to Smn2B/− mice. Our study shows that necroptosis modulates survival, motor behavior and muscle fiber size independent of SMN levels and independent of neurodegeneration. Thus, small-molecule inhibitors of necroptosis as a combinatorial approach together with SMN-restoring drugs could be a future strategy for the treatment of SMA.

脊髓性肌萎缩症（Spinal muscular atrophy, SMA）是一种由运动神经元生存蛋白（Survival Motor Neuron, SMN）表达水平低下所引发的单基因神经肌肉疾病，运动神经元变性是该病的核心病理特征。然而，SMN蛋白广泛表达于全身各组织，在外周组织中耗竭该蛋白可引发独立于神经变性的固有疾病表型，包括肌肉缺陷。目前获批的恢复SMN水平的治疗手段已使SMA患者获得显著的临床改善，但仍有大量患者对该治疗无应答，这凸显了开发无需仅依赖恢复SMN的辅助治疗策略的迫切需求。失调的细胞死亡通路是SMA中不依赖SMN的致病机制的潜在候选靶点。受体相互作用蛋白激酶1（Receptor-interacting protein kinase 1, RIPK1）与RIPK3已被广泛认定为坏死性凋亡（necroptosis）——一种重要的程序性细胞死亡形式——的关键治疗靶点。此外，半胱天冬酶-1（Caspase-1）在炎症反应与细胞死亡过程中发挥核心作用。本研究探究了坏死性凋亡，尤其是RIPK3与Caspase-1，在SMA的Smn2B/−小鼠模型中的作用。我们构建了三重突变体（TKO）小鼠：Smn2B/−; Ripk3−/−; Casp1−/−。与Smn2B/−小鼠相比，TKO小鼠的存活时长显著延长，运动功能也得到改善。尽管TKO小鼠无法阻止运动神经元丢失或神经肌肉接头病理改变，但相较于Smn2B/−小鼠，其肌纤维体积更大。本研究证实，坏死性凋亡可在不依赖SMN水平与神经变性的前提下，调控机体存活、运动行为与肌纤维大小。因此，将坏死性凋亡小分子抑制剂与恢复SMN的药物联合使用，有望成为未来治疗SMA的全新策略。