論文

Immune checkpoint molecules have emerged as regulators of microglial function in neurodegenerative diseases. We previously demonstrated that LAG-3 shapes disease-associated microglial phenotypes in ALS and that germline LAG-3 deletion in SOD1G93A mice accelerated disease onset but extended duration, leaving survival unchanged. Here, we investigated the therapeutic efficacy of anti-LAG-3 antibody treatment starting after symptom onset. Anti-LAG-3 treatment extended survival, slowed neurological and motor decline, preserved body weight and motor neurons, and reduced microgliosis. Within microglia, the Axl+ phagocytic-module fraction increased while the Dectin-1+ inflammatory-module fraction decreased. These findings indicate that post-onset LAG-3 inhibition is a promising therapeutic strategy for ALS.

Immune checkpoint molecules, inhibitory receptors originally characterized in T cell biology, have recently emerged as regulators of microglial function in neurodegeneration, yet their roles in amyotrophic lateral sclerosis (ALS) remain unexplored. Here, we investigated LAG-3, an inhibitory immune checkpoint receptor, in microglial regulation during ALS pathogenesis using SOD1G93A mice. LAG-3 expression was progressively upregulated in spinal cord microglia during disease progression, and LAG-3-high microglia exhibited a disease-associated microglia (DAM) transcriptional signature. Genetic deletion of LAG-3 produced a biphasic phenotype, with accelerated disease onset but significantly prolonged disease duration. LAG-3 deficiency enhanced inflammatory microglial responses at the early disease stage, whereas at the late stage it suppressed inflammatory signaling while selectively preserving phagocytic effector gene expression, demonstrating that LAG-3 dissociates the inflammatory and phagocytic modules within the DAM program in a stage-dependent manner. These transcriptional changes translated into enhanced phagocytic capacity in primary microglia and amelioration of the spinal cord environment through suppression of inflammatory pathways and restoration of oxidative phosphorylation. Our findings identify LAG-3 as a stage-dependent regulator of microglial functional states in ALS and support the concept that immune checkpoint molecules constitute a class of module-level regulators of microglial function in neurodegeneration.

Microglia are resident innate immune cells in the central nervous system (CNS) and play important roles in the development of CNS homeostasis. Excessive activation and neurotoxicity of microglia are observed in several CNS disorders, but the mechanisms regulating their activation remain unclear. Immune checkpoint molecules are expressed on activated immune cells and regulate their activation in peripheral immunity. However, the expression mechanism of immune checkpoint molecules in activated microglia is still unknown. Here, we analyzed the expression of immune checkpoint molecules in activated microglia using the mouse microglial cell line BV2 and primary cultured microglia. The expression of lymphocyte activation gene-3 (LAG-3), a type of immune checkpoint molecule, was increased in microglia activated by IFN-γ. IFN-γ-induced LAG-3 expression in microglia was suppressed by transfection of siRNA targeting STAT1. LAG-3 has two forms, membrane and soluble, and both forms were upregulated in microglia activated by IFN-γ. The production of soluble LAG-3 was suppressed by treatment with inhibitors of metalloproteinases such as ADAM10 and ADAM17. IFN-γ administration into cisterna magna of mice increased LAG-3 expression in spinal microglia. Furthermore, LAG-3 knockdown in microglia promoted nitric oxide production by IFN-γ. Our results demonstrate that LAG-3 expression in microglia is induced by the IFN-γ-STAT1 pathway and soluble LAG-3 production is regulated via cleavage of membranous LAG-3 by metalloproteinases including ADAM10 and ADAM17.

Animals on Earth need to hold postures and execute a series of movements under gravity and atmospheric pressure. VAChT-Cre is a transgenic Cre driver mouse line that expresses Cre recombinase selectively in motor neurons of S-type (slow-twitch fatigue-resistant) and FR-type (fast-twitch fatigue-resistant). Sequential motor unit recruitment is a fundamental principle for fine and smooth locomotion; smaller-diameter motor neurons (S-type, FR-type) first contract low-intensity oxidative type I and type IIa muscle fibers, and thereafter larger-diameter motor neurons (FInt-type, FF-type) are recruited to contract high-intensity glycolytic type IIx and type IIb muscle fibers. To selectively eliminate S- and FR-type motor neurons, VAChT-Cre mice were crossbred with NSE-DTA mice in which the cytotoxic diphtheria toxin A fragment (DTA) was expressed in Cre-expressing neurons. The VAChT-Cre;NSE-DTA mice were born normally but progressively manifested various characteristics, including body weight loss, kyphosis, kinetic and postural tremor, and muscular atrophy. The progressive kinetic and postural tremor was remarkable from around 20 weeks of age and aggravated. Muscular atrophy was apparent in slow muscles, but not in fast muscles. The increase in motor unit number estimation was detected by electromyography, reflecting compensatory re-innervation by remaining FInt- and FF-type motor neurons to the orphaned slow muscle fibers. The muscle fibers gradually manifested fast/slow hybrid phenotypes, and the remaining FInt-and FF-type motor neurons gradually disappeared. These results suggest selective ablation of S- and FR-type motor neurons induces progressive muscle fiber-type transition, exhaustion of remaining FInt- and FF-type motor neurons, and late-onset kinetic and postural tremor in mice.