SBT-272 improves TDP-43 pathology in the ALS motor cortex by modulating mitochondrial integrity, motility, and function

Mitochondrial defects are one of the common underlying causes of neuronal vulnerability in motor neuron diseases, such as amyotrophic lateral sclerosis (ALS), and TDP-43 pathology is the most common proteinopathy in ALS. Disrupted inner mitochondrial membrane (IMM) reported in the upper motor neurons (UMNs) of ALS patients with TDP-43 pathology is recapitulated in the UMNs of well-characterized mutant hTDP-43 mouse models of ALS. The construct validity, such as common cellular pathology in mice and human, offers a unique opportunity to test treatment strategies that may translate. SBT-272 is a well-tolerated brain-penetrant small molecule that stabilizes cardiolipin, a phospholipid found in IMM, thereby restoring mitochondrial structure and respiratory function. We investigated whether SBT-272 can improve IMM structure and health in UMNs diseased with TDP-43 pathology in our well-characterized UMN reporter line for ALS. We found that SBT-272 significantly improved mitochondrial structural integrity and restored mitochondrial motility and function. This led to improved health of diseased UMNs in vitro. In comparison to edaravone and AMX0035, SBT-272 appeared more effective in restoring health of diseased UMNs. Chronic treatment of SBT-272 for sixty days starting at an early symptomatic stage of the disease in vivo led to a reduction in astrogliosis, microgliosis, and retention of UMN degeneration in the ALS motor cortex. Our results underscore the therapeutic potential of SBT-272, especially within the context of TDP-43 pathology and mitochondrial dysfunction. Highlights 1. Early and progressive upper motor neuron (UMN) degeneration defines ALS pathology 2. Mitochondrial defects are prominent and common in UMNs with TDP-43 pathology 3. SBT-272 treatment improves mitochondrial stability, mobility and function 4. SBT-272 treatment reduces astrogliosis, microgliosis and improves UMN health ### Competing Interest Statement The authors have declared no competing interest. * ADP : Adenosine Diphosphate ALS : Amyotrophic lateral sclerosis ANOVA : Analysis of variance ATP : Adenosine Triphosphate BSA : Bovine serum albumin CHCHD3 : Coiled-Coil-Helix-Coiled-Coil-Helix Domain-Containing Protein 3 CL : Cardiolipin CLEM : Correlative light electron microscopy CSMN : Corticospinal motor neurons CTIP2 : COUP-TF-interacting protein 2 DIV : Days in-vitro eGFP : Enhanced green fluorescent protein EM : Electron microscopy ET-1 : Endothelial toxin-1 FTLD : Frontotemporal lobar degeneration GI : Gastrointestinal IHC : Immunohistochemistry IMM : Inner mitochondrial membrane mSOD1 : mutated superoxide dismutase 1 OMM : Outer mitochondrial membrane OXPHOS : Oxidative phosphorylation PFA : Paraformaldehyde P3 : Postnatal day 3 ROS : Reactive oxygen species ROX : Residual oxygen consumption SFM : Serum free medium TMPD : N,N,N’,N’-Tetramethyl-p-phenylenediamine dihydrochloride TDP-43 : TARDNA binding protein 43 UCHL1 : Ubiquitin C-Terminal Hydrolase L1 UMN : Upper motor neuron VCP : Valosin-containing protein