Deciphering the physiological role of Spastin for the regulation of Store Operated Calcium Entry and its pathological consequences in iPSC Derived SPG4 Neurons

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Hereditary Spastic Paraplegia is a genetically and clinically heterogeneous group of monogenic motor neuron disease. Corticospinal tract degeneration is the common structural feature leading to spasticity of the lower limbs. Mutations in SPG4, also referred as SPAST, are the most frequent cause of HSP and found in up to 40% of all autosomal dominant HSP cases. Spastin´s microtubule severing activity has been extensively studied. However, its precise interaction with the ER remains elusive. Multiple lines of evidence support the localization of Spastin within the ER, and interaction with the ER shaping proteins. Very little is known about how Spastin-associated changes in ER structure may affect its function. Our preliminary findings indicate a direct effect of Spastin on Store-operated Calcium entry (SOCE). Therefore, we hypothesize that direct interaction of Spastin with ER component modulates ER function and cellular Ca2+ homeostasis. Since Spastin is the most commonly mutated protein in HSP, additionally we aim to determine effects of pathogenic SOCE activity in a human neuronal model of HSP. To investigate these hypotheses, we propose to decipher the molecular function of Spastin in SOCE. We will investigate Spastin dose dependent effects on cellular calcium homeostasis. In the next step we will dissect Spastin-dependent SOCE effects on HSP pathology. Since human cortical neurons are difficult to study in human intact brains, iPSC technology will be used to generate and investigate SPG4-dependnet SOCE effects on HSP pathology in neurons. Specifically, we will expand the study of Spastin’s role in SOCE using hiPSC cortical neurons, delineate morphological, electrophysiological and transcriptional effects of impaired SOCE in HSP and explore SOCE impairment as a common pathogenic mechanism of action in HSP.