Improving mitochondria and ER stability helps eliminate upper motor neuron degeneration that occurs due to mSOD1 toxicity and TDP‐43 pathology

Abstract

Background Upper motor neurons (UMNs) are a key component of motor neuron circuitry. Their degeneration is a hallmark for diseases, such as hereditary spastic paraplegia (HSP), primary lateral sclerosis (PLS), and amyotrophic lateral sclerosis (ALS). Currently there are no preclinical assays investigating cellular responses of UMNs to compound treatment, even for diseases of the UMNs. The basis of UMN vulnerability is not fully understood, and no compound has yet been identified to improve the health of diseased UMNs: two major roadblocks for building effective treatment strategies. Methods Novel UMN reporter models, in which UMNs that are diseased because of misfolded superoxide dismutase protein (mSOD1) toxicity and TDP‐43 pathology are labeled with eGFP expression, allow direct assessment of UMN response to compound treatment. Electron microscopy reveals very precise aspects of endoplasmic reticulum (ER) and mitochondrial damage. Administration of NU‐9, a compound initially identified based on its ability to reduce mSOD1 toxicity, has profound impact on improving the health and stability of UMNs, as identified by detailed cellular and ultrastructural analyses. Results Problems with mitochondria and ER are conserved in diseased UMNs among different species. NU‐9 has drug‐like pharmacokinetic properties. It lacks toxicity and crosses the blood brain barrier. NU‐9 improves the structural integrity of mitochondria and ER, reduces levels of mSOD1, stabilizes degenerating UMN apical dendrites, improves motor behavior measured by the hanging wire test, and eliminates ongoing degeneration of UMNs that become diseased both because of mSOD1 toxicity and TDP‐43 pathology, two distinct and important overarching causes of motor neuron degeneration. Conclusions Mechanism‐focused and cell‐based drug discovery approaches not only addressed key cellular defects responsible for UMN loss, but also identified NU‐9, the first compound to improve the health of diseased UMNs, neurons that degenerate in ALS, HSP, PLS, and ALS/FTLD patients.

Mitochondrial dysregulation occurs early in ALS motor cortex with TDP-43 pathology and suggests maintaining NAD+ balance as a therapeutic strategy

“…In an effort to investigate whether NMN treatment would have an impact on the health of UMNs diseased with TDP-43 pathology, we utilized dissociated motor cortex cultures established from prpTDP-43 A315T -UeGFP mice, in which CSMN are genetically labeled with eGFP expression that is stable and long-lasting, and when in culture retain their CSMN identity and eGFP expression. These diseased reporter mice were exceptionally valuable for directly assessing the cellular responses of healthy and diseased CSMN to treatments in vitro and in vivo 69 – 71 . Here, we utilized them to investigate their response to NMN treatment.…”

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

“…The brain was dissected out followed by post-fixation in 4% paraformaldehyde overnight and sectioned at 50μm using a Leica vibratome (Leica VT1000S, Leica Inc., Germany). Serial floating sections (300μm apart) were processed for GFP, GFAP, and Iba1 immunohistochemistry, as described (Genc et al, 2021; Jara et al, 2019).…”

Nanotechnology-Based Drug Delivery Strategies to Repair the Mitochondrial Function in Neuroinflammatory and Neurodegenerative Diseases

“…The enzyme SOD1 is mainly a cytosolic molecule, but mutated forms of SOD1 have been localized in aggregates associated with mitochondria in transgenic mouse models and patients with familial ALS [77,78]. Interestingly, the pharmacological reduction of misfolded SOD1 restored the structural integrity of mitochondria, reduced degeneration of motor neurons, and attenuated motor deficits in a transgenic ALS mouse model [99].…”