N88S seipin mutant transgenic mice develop features of seipinopathy/BSCL2-related motor neuron disease via endoplasmic reticulum stress

Heterozygosity for mutations (N88S and P90L) in the N-glycosylation site of seipin/BSCL2 is associated with the autosomal dominant motor neuron diseases, spastic paraplegia 17 and distal hereditary motor neuropathy type V, referred to as 'seipinopathies'. Previous in vitro studies have shown that seipinopathy-linked mutations result in accumulation of unfolded proteins in the endoplasmic reticulum (ER), leading to the unfolded protein response and cell death, suggesting that seipinopathies is closely associated with ER stress. To further understand the molecular pathogenesis of seipinopathies, we generated a transgenic (tg) mouse line expressing the human N88S seipin mutant with the murine Thy-1 promoter to permit analyses of in vivo phenotypic changes. The N88S seipin tg mice develop a progressive spastic motor deficit, reactive gliosis in the spinal cord and neurogenic muscular atrophy, recapitulating the symptomatic and pathological phenotype in patients of seipinopathy. We also found that expression of mutant seipin in mice upregulated the ER stress marker, immunoglobulin-heavy-chain-binding protein, protein disulfide isomerase and X-box binding protein 1, but was not linked to significant neuronal loss in affected tissue, thereby indicating that ER stress is sufficient, while neuronal death is not necessary, for the development of motor phenotypes of seipinopathies. Our findings in the mutant seipin tg mouse provide clues to understand the relationship with ER stress and neurodegeneration, and the seipin tg mouse is a valid tool for the development of novel therapeutic strategies against ER stress-related diseases.