Koji Yamanaka

Loss-of-function mutations in TANK-binding kinase 1 (TBK1) cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), characterized by cytoplasmic aggregation of TAR DNA-binding protein 43 (TDP-43), known as TDP-43 pathology, but the mechanisms beyond impaired autophagy remain undefined. Here, we identify a TBK1-IFNβ-immunoproteasome axis as a novel autophagy-independent proteostatic pathway regulating TDP-43 clearance. TBK1 is activated by aggregation-prone monomeric TDP-43 via physical association, and this activation alleviates TDP-43 pathology in neuronal cells. TBK1 subsequently induces IFNβ expression, which upregulates the immunoproteasome to promote degradation of monomeric TDP-43 in neurons, including human iPSC-derived lower motor neurons. Importantly, IFNβ receptor expression is downregulated in spinal motor neurons from ALS patients with TDP-43 pathology. Furthermore, heterozygous Tbk1 deletion in SOD1 ^G93A mice impairs immunoproteasome induction and increases polyubiquitinated protein accumulation in spinal cords, supporting the in vivo relevance of this pathway. Collectively, our findings reveal that impairment of the TBK1-IFNβ-immunoproteasome axis represents an autophagy-independent mechanism contributing to the development of TDP-43 pathology in ALS and FTD.

The brain is a lipid-rich organ, with myelin sheaths containing exceptionally high levels of lipids. Oligodendrocyte dysfunction and myelin lipid deregulation have been implicated in Alzheimer’s disease (AD), yet their precise roles remain unclear. In this study, we examined lipid metabolic alterations, with focus on primary myelin lipids, in App^{NL−G−F/NL−G−F} (App) AD model mice fed either a normal control diet (NCD) or a high-fat diet (HFD). Brain lipid profiles were altered in App mice, with differential effects depending on diet. Notably, oligodendrocyte gene expression patterns, including those involved in myelin lipid metabolic pathways, were similar between NCD- and HFD-fed App mice and did not correspond with the observed changes in brain lipid composition. This discrepancy indicates that myelin lipid homeostasis in the AD brain is regulated by mechanisms beyond transcriptional control, likely involving post-translational regulation, inter-glial metabolic interactions, and brain-periphery lipid exchange. Importantly, HFD intake did not exacerbate cognitive impairment or neuroinflammation in App mice; rather, HFD-fed App mice showed improved learning during behavioral testing and reduced astrocytic activation. These findings suggest that dietary fat intake does not worsen—and may partially ameliorate—certain aspect of AD pathology, highlighting the complex and context-dependent relationship between metabolic interventions and neurodegenerative disease.

Loss-of-function mutations in TANK-binding kinase 1 (TBK1) are genetically linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), and induce cytoplasmic aggregation of TAR DNA-binding protein 43 (TDP-43), known as TDP-43 pathology. Although TBK1 deficiency is thought to contribute to TDP-43 pathology primarily through impaired autophagy, the full spectrum of its pathological impact remains unclear. Given the multifunctional nature of TBK1, alternative pathways beyond autophagy are possibly involved in TDP-43 pathology. Here, we found that TBK1 alleviates TDP-43 pathology in neuronal cells via induction of interferon-beta (IFNβ), and that the IFNβ receptor is downregulated in spinal motor neurons from ALS patients with TDP-43 pathology. We further demonstrated that IFNβ induces the immunoproteasome by upregulating its subunits, thereby promoting the degradation of aggregation-prone monomeric TDP-43. Furthermore, heterozygous deletion of Tbk1 in SOD1 ^G93A ALS model mice resulted in reduced immunoproteasome induction and increased polyubiquitinated protein accumulation in the spinal cord. These findings suggest that impairment of the TBK1-IFNβ-immunoproteasome axis may contribute to the development of TDP-43 pathology in ALS and FTD.

Recent evidence indicates that the mitochondria–endoplasmic reticulum (ER) contact site is a novel microdomain essential for cellular homeostasis. Various proteins are accumulated at the mitochondria‐associated membrane (MAM), an ER subcomponent closely associated with the mitochondria, contributing to Ca²⁺ transfer to the mitochondria, lipid synthesis, mitochondrial fission/fusion, and autophagy. These functions are disrupted in the diseases, particularly in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Alzheimer's disease. In this review, we summarize the disruption of protein homeostasis in various neurodegenerative diseases, present recent works on the mechanisms of MAM aberration, including ours mainly focused on ALS, and then discuss challenges and prospects for future MAM‐targeted therapies in neurodegenerative diseases.

Alzheimer’s disease (AD) is the leading neurodegenerative disease manifesting cognitive impairment. Its procession is regulated by activated glial cell–mediated neuroinflammation. Although estrogen deprivation is a known risk factor for AD in females, the impact of androgen deprivation on AD pathology in males, particularly regarding neuroinflammation, remains unclear. This study investigates the effects of long-term systemic androgen deprivation on AD pathology, including glial cell–specific gene expression, amyloid β (Aβ) pathology, and cognitive function in male castrated App^{NL−G−F/NL−G−F} (App) mice. We found significantly reduced androgen receptor (AR/Ar) expression levels in the precunei of male patients with early AD pathology and isolated brain microglia of male App mice compared with their nonpathological controls. In castrated App mice, microglial Tnf and Il6 and astrocytic Socs3 were downregulated, indicating that androgens may promote inflammation in the brain. However, Aβ accumulation and cognitive function were unaffected. These results suggest that although systemic androgen deprivation modulates neuroinflammation, the changes are insufficient to alter the AD phenotype or pathology in male App mice.