Drosophila assays of movement and mitochondria included in study of an autosomal dominant spastic paraplegia and dystonia

Mov Disord. 2021 Oct 11. doi: 10.1002/mds.28821

A Novel Variant of ATP5MC3 Associated with Both Dystonia and Spastic Paraplegia

Neilson DE, Zech M, Hufnagel RB, Slone J, Wang X, Homan S, Gutzwiller LM, Leslie EJ, Leslie ND, Xiao J, Hedera P, LeDoux MS, Gebelein B, Wilbert F, Eckenweiler M, Winkelmann J, Gilbert DL, Huang T

Abstract:

BACKGROUND: In a large pedigree with an unusual phenotype of spastic paraplegia or dystonia and autosomal dominant inheritance, linkage analysis previously mapped the disease to chromosome 2q24-2q31.

OBJECTIVE: The aim of this study is to identify the genetic cause and molecular basis of an unusual autosomal dominant spastic paraplegia and dystonia.

METHODS: Whole exome sequencing following linkage analysis was used to identify the genetic cause in a large family. Cosegregation analysis was also performed. An additional 384 individuals with spastic paraplegia or dystonia were screened for pathogenic sequence variants in the adenosine triphosphate (ATP) synthase membrane subunit C locus 3 gene (ATP5MC3). The identified variant was submitted to the "GeneMatcher" program for recruitment of additional subjects. Mitochondrial functions were analyzed in patient-derived fibroblast cell lines. Transgenic Drosophila carrying mutants were studied for movement behavior and mitochondrial function.

RESULTS: Exome analysis revealed a variant (c.318C > G; p.Asn106Lys) (NM_001689.4) in ATP5MC3 in a large family with autosomal dominant spastic paraplegia and dystonia that cosegregated with affected individuals. No variants were identified in an additional 384 individuals with spastic paraplegia or dystonia. GeneMatcher identified an individual with the same genetic change, acquired de novo, who manifested upper-limb dystonia. Patient fibroblast studies showed impaired complex V activity, ATP generation, and oxygen consumption. Drosophila carrying orthologous mutations also exhibited impaired mitochondrial function and displayed reduced mobility.

CONCLUSION: A unique form of familial spastic paraplegia and dystonia is associated with a heterozygous ATP5MC3 variant that also reduces mitochondrial complex V activity.

DOI: 10.1002/mds.28821
PMID: 34636445

Uncovering the cellular function of Torsins -- relevance to DYT1 dystonia

Grillet M, Dominguez Gonzalez B, Sicart A, Pöttler M, Cascalho A, Billion K, Hernandez Diaz S, Swerts J, Naismith TV, Gounko NV, Verstreken P, Hanson PI, Goodchild RE. Torsins Are Essential Regulators of Cellular Lipid Metabolism. Dev Cell. 2016 Jul 14. PMID: 27453503.

From the abstract: "Torsins are developmentally essential AAA+ proteins, and mutation of human torsinA causes the neurological disease DYT1 dystonia. They localize in the ER membranes, but their cellular function remains unclear. We now show that dTorsin is required in Drosophila adipose tissue, where it suppresses triglyceride levels, promotes cell growth, and elevates membrane lipid content. We also see that human torsinA at the inner nuclear membrane is associated with membrane expansion and elevated cellular lipid content. ... These findings identify that torsins are essential regulators of cellular lipid metabolism and implicate disturbed lipid biology in childhood-onset DYT1 dystonia."

Dystonia models. Recent review.

Caldwell KA, Shu Y, Roberts NB, Caldwell GA, O'Donnell JM. Invertebrate models of dystonia. Curr Neuropharmacol. 2013 Jan;11(1):16-29. PMID: 23814534; PMCID: PMC3580786.

From the abstract: "Despite the substantial advances resulting from the identification of these loci, the function of many DYT gene products remains unclear. ... [Worm and fly] models are particularly amenable to large-scale genetic screens for modifiers or additional alleles, which are bolstering our understanding of the molecular functions associated with these gene products. Moreover, the use of invertebrate models for the evaluation of DYT genetic loci and their genetic interaction networks has predictive value and can provide a path forward for therapeutic intervention."