Postdoctoral Fellow The University of Hong Kong Hong Kong, Hong Kong
Abstract: Spinal muscular atrophy (SMA) is a neuromuscular disease caused by the loss of the ubiquitously expressed survival motor neuron (SMN) protein, which is essential for the biogenesis of spliceosome complex, resulting in the selective degeneration of spinal motor neurons (MNs). Based on the onset of disease, SMA disease is clarified to type I, II and III, and type I represents the most severe type. While current SMN-enhancing therapies have shown promise in reducing disease severity, they do not reverse motor axon degeneration, leading to a limited locomotor recovery. Moreover, the mechanism underlying the specific loss of MNs remains unknown. Here, we used single-cell transcriptomics to examine alterations in cellular populations and gene expression in neuromuscular organoids (NMOs) derived from the urine cells of patients with SMA type I, II and III compared to those from healthy individuals. These NMOs self-organize into two distinct compartments comprising neural and muscle lineages. In the mature spinal cord neuron and neural progenitors cluster, there is a significant decrease in pre-mRNA splicing related genes such as HNRNPC, RBM25, SRSF2 and MYEF2, which may be caused by the deficiency of SMN protein. We confirmed a marked reduction in MN formation in neuromuscular organoids (NMOs) derived from SMA patients. When comparing the gene expression of the residual MN cluster in SMA patients to that of healthy individuals, we detected a decreased expression of genes involved in axonal outgrowth and cytoskeletal integrity in axon such as SHTN1, NEFL, NEFM, DCC, DCX, MAPT, suggesting defective axonal projection in SMA patients’ MNs. Consistently, these NMOs showed defective formation of neuromuscular junctions (NMJs) and increased cell death as shown by immunofluorescence staining. In summary, our findings provide insights into the cellular and molecular basis that underlie the impaired function of MNs, muscles, and NMJs in SMA patients, paving the way for identifying new therapeutic targets to restore motor axonal outgrowth and NMJ formation.
Funding Source: Research Grants Council and the University Grants Council of HK (GRF_17114619, GRF_17102420, R7018-23F), URC Seed Fund for Collaborative Research 2022/2023.
.jpg "Tianyuan Shi, PhD (she/her/hers) photo")