Amyotrophic lateral sclerosis

Genetic Ablation of Sarm1 Mitigates Disease Acceleration after Traumatic Brain Injury in the SOD1G93A Transgenic Mouse Model of Amyotrophic Lateral Sclerosis

OBJECTIVE

Approximately 20% of familial cases of amyotrophic lateral sclerosis (ALS) are caused by mutations in the gene encoding superoxide dismutase 1 (SOD1). Epidemiological data have identified traumatic brain injury (TBI) as an exogenous risk factor for ALS; however, the mechanisms by which TBI may worsen SOD1 ALS remain largely undefined.

METHODS

We sought to determine whether repetitive TBI (rTBI) accelerates disease onset and progression in the transgenic SOD1G93A mouse ALS model, and whether loss of the primary regulator of axonal degeneration sterile alpha and TIR motif containing 1 (Sarm1) mitigates the histological and behavioral pathophysiology. We subjected wild-type (n = 23), Sarm1 knockout (KO; n = 17), SOD1G93A (n = 19), and SOD1G93AxSarm1KO (n = 26) mice of both sexes to rTBI or sham surgery at age 64 days (62-68 days). Body weight and ALS-deficit score were serially assessed up to 17 weeks after surgery and histopathology assessed in layer V of the primary motor cortex at the study end point.

RESULTS

In sham injured SOD1G93A mice, genetic ablation of Sarm1 did not attenuate axonal loss, improve neurological deficits, or survival. The rTBI accelerated onset of G93A-SOD1 ALS, as indicated by accentuated body weight loss, earlier onset of hindlimb tremor, and shortened survival. The rTBI also triggered TDP-43 mislocalization, enhanced axonal and neuronal loss, microgliosis, and astrocytosis. Loss of Sarm1 significantly diminished the impact of rTBI on disease progression and rescued rTBI-associated neuropathology.

INTERPRETATION

SARM1-mediated axonal death pathway promotes pathogenesis after TBI in SOD1G93A mice suggesting that anti-SARM1 therapeutics are a viable approach to preserve neurological function in injury-accelerated G93A-SOD1 ALS. ANN NEUROL 2025.

Decreased spinal cord motor neuron numbers in mice depleted of central nervous system copper

Disrupted copper availability in the central nervous system (CNS) is implicated as a significant feature of the neurodegenerative disease amyotrophic lateral sclerosis (ALS). Solute carrier family 31 member 1 (Slc31a1; Ctr1) governs copper uptake in mammalian cells and mutations affecting Slc31a1 are associated with severe neurological abnormalities. Here, we examined the impact of decreased CNS copper caused by ubiquitous heterozygosity for functional Slc31a1 on spinal cord motor neurons in Slc31a1+/- mice. Congruent with the CNS being relatively susceptible to disrupted copper availability, brain and spinal cord tissue from Slc31a1+/- mice contained significantly less copper than wild-type littermates, even though copper levels in other tissues were unaffected. Slc31a1+/- mice had less spinal cord α-motor neurons compared to wild-type littermates, but they did not develop any overt physical signs of motor impairment. By contrast, ALS model SOD1G37R mice had fewer α-motor neurons than control mice and exhibited clear signs of motor function impairment. With the expression of Slc31a1 notwithstanding, spinal cord expression of genes related to copper handling revealed only minor differences between Slc31a1+/- and wild-type mice. This contrasted with SOD1G37R mice where changes in the expression of copper handling genes were pronounced. Similarly, the expression of genes related to toxic glial activation was unchanged in spinal cords from Slc31a1+/- mice but highly upregulated in SOD1G37R mice. Together, results from the Slc31a1+/- mice and SOD1G37R mice indicate that although depleted CNS copper has a significant impact on spinal cord motor neuron numbers, the manifestation of overt ALS-like motor impairment requires additional factors.

PAD2 dysregulation and aberrant protein citrullination feature prominently in reactive astrogliosis and myelin protein aggregation in sporadic ALS

Alteration in protein citrullination (PC), a common posttranslational modification (PTM), contributes to pathogenesis in various inflammatory disorders. We previously reported that PC and protein arginine deiminase 2 (PAD2), the predominant enzyme isoform that catalyzes this PTM in the central nervous system (CNS), are altered in mouse models of amyotrophic lateral sclerosis (ALS). We now demonstrate that PAD2 expression and PC are altered in human postmortem ALS spinal cord and motor cortex compared to controls, increasing in astrocytes while trending lower in neurons. Furthermore, PC is enriched in protein aggregates that contain the myelin proteins PLP and MBP in ALS. These results confirm our findings in ALS mouse models and suggest that altered PAD2 and PC contribute to neurodegeneration in ALS.

Astrocyte-Neuron Interactions Contributing to Amyotrophic Lateral Sclerosis Progression

Amyotrophic lateral sclerosis (ALS) is a complex disease impacting motor neurons of the brain, brainstem, and spinal cord. Disease etiology is quite heterogeneous with over 40 genes causing the disease and a vast ~90% of patients having no prior family history. Astrocytes are major contributors to ALS, particularly through involvement in accelerating disease progression. Through study of genetic forms of disease including SOD1, TDP43, FUS, C9orf72, VCP, TBK1, and more recently patient-derived cells from sporadic individuals, many biological mechanisms have been identified to cause intrinsic or glial-mediated neurotoxicity to motor neurons. Overall, many of the normally supportive and beneficial roles that astrocytes contribute to neuronal health and survival instead switch to become deleterious and neurotoxic. While the exact pathways may differ based on disease-origin, altered astrocyte-neuron communication is a common feature of ALS. Within this chapter, distinct genetic forms are examined in detail, along with what is known from sporadic patient-derived cells. Overall, this chapter highlights the interplay between astrocytes and neurons in this complex disease and describes the key features underlying: astrocyte-mediated motor neuron toxicity, excitotoxicity, oxidative/nitrosative stress, protein dyshomeostasis, metabolic imbalance, inflammation, trophic factor withdrawal, blood-brain/blood-spinal cord barrier involvement, disease spreading, and the extracellular matrix/cell adhesion/TGF-β signaling pathways.

[Promising approaches to the pathogenetic therapy of amyotrophic lateral sclerosis]

Amyotrophic lateral sclerosis is a severe incurable disease of the nervous system. Currently only methods of palliative care for the patients with this disease are available. Few medications for the pathogenetic therapy are registered in some countries, i.e. riluzole, edaravon, sodium phenylbutyrate/taurursodiol as well as tofersen (conditionally). Their efficacy is relatively low. The main directions in the development of pathogenetic therapy of ALS include gene therapy, use of stem cells, immunomodulators, agents affecting gut microbiota. A search is also underway for low-molecular compounds with neuroprotective and antioxidant properties. Perspective direction is prevention of ALS. This will be possible when biomarkers for identification of patients in pre-manifest/prodromal stage are detected.