Mitochondrial Function in Hereditary Spastic Paraplegia: Deficits in SPG7 but Not SPAST Patient-Derived Stem Cells

Gautam Wali; Kishore Raj Kumar; Erandhi Liyanage; Ryan L Davis; Alan Mackay-Sim; Carolyn M Sue

doi:10.3389/fnins.2020.00820

Mitochondrial Function in Hereditary Spastic Paraplegia: Deficits in SPG7 but Not SPAST Patient-Derived Stem Cells

Front Neurosci. 2020 Aug 20:14:820. doi: 10.3389/fnins.2020.00820. eCollection 2020.

Authors

Gautam Wali^{1

2}, Kishore Raj Kumar^{1

2

3

4

5}, Erandhi Liyanage¹, Ryan L Davis^{1

2

4}, Alan Mackay-Sim^{2

6}, Carolyn M Sue^{1

2

5}

Affiliations

¹ Department of Neurogenetics, Royal North Shore Hospital, Kolling Institute of Medical Research, The University of Sydney, Sydney, NSW, Australia.
² Faculty of Medicine and Health, Sydney Medical School, The University of Sydney, Sydney, NSW, Australia.
³ Molecular Medicine Laboratory, Department of Neurology, Concord Hospital, Sydney, NSW, Australia.
⁴ Kinghorn Centre for Clinical Genomics, Garvan Institute of Medical Research, Sydney, NSW, Australia.
⁵ Department of Neurology, Royal North Shore Hospital, Northern Sydney Local Health District, Sydney, NSW, Australia.
⁶ Griffith Institute for Drug Discovery, Griffith University, Brisbane, QLD, Australia.

Abstract

Mutations in SPG7 and SPAST are common causes of hereditary spastic paraplegia (HSP). While some SPG7 mutations cause paraplegin deficiency, other SPG7 mutations cause increased paraplegin expression. Mitochondrial function has been studied in models that are paraplegin-deficient (human, mouse, and Drosophila models with large exonic deletions, null mutations, or knockout models) but not in models of mutations that express paraplegin. Here, we evaluated mitochondrial function in olfactory neurosphere-derived cells, derived from patients with a variety of SPG7 mutations that express paraplegin and compared them to cells derived from healthy controls and HSP patients with SPAST mutations, as a disease control. We quantified paraplegin expression and an extensive range of mitochondrial morphology measures (fragmentation, interconnectivity, and mass), mitochondrial function measures (membrane potential, oxidative phosphorylation, and oxidative stress), and cell proliferation. Compared to control cells, SPG7 patient cells had increased paraplegin expression, fragmented mitochondria with low interconnectivity, reduced mitochondrial mass, decreased mitochondrial membrane potential, reduced oxidative phosphorylation, reduced ATP content, increased mitochondrial oxidative stress, and reduced cellular proliferation. Mitochondrial dysfunction was specific to SPG7 patient cells and not present in SPAST patient cells, which displayed mitochondrial functions similar to control cells. The mitochondrial dysfunction observed here in SPG7 patient cells that express paraplegin was similar to the dysfunction reported in cell models without paraplegin expression. The p.A510V mutation was common to all patients and was the likely species associated with increased expression, albeit seemingly non-functional. The lack of a mitochondrial phenotype in SPAST patient cells indicates genotype-specific mechanisms of disease in these HSP patients.

Keywords: SPAST; SPG7; hereditary spastic paraplegia; mitochondria; oxidative phosphorylation; paraplegin; spastin.