Mitochondria-associated membrane collapse impairs TBK1-mediated proteostatic stress response in ALS.

The organelle contact site of the endoplasmic reticulum and mitochondria, known as the mitochondria-associated membrane (MAM), is a multifunctional microdomain in cellular homeostasis. We previously reported that MAM disruption is a common pathological feature in amyotrophic lateral sclerosis (ALS); however, the precise role of MAM in ALS was uncovered. Here, we show that the MAM is essential for TANK-binding kinase 1 (TBK1) activation under proteostatic stress conditions. A MAM-specific E3 ubiquitin ligase, autocrine motility factor receptor, ubiquitinated nascent proteins to activate TBK1 at the MAM, which results in ribosomal protein degradation. MAM or TBK1 deficiency under proteostatic stress conditions resulted in increased cellular vulnerability in vitro and motor impairment in vivo. Thus, MAM disruption exacerbates proteostatic stress via TBK1 inactivation in ALS. Our study has revealed a proteostatic mechanism mediated by the MAM-TBK1 axis, highlighting the physiological importance of the organelle contact sites.

Label-free cell detection of acute leukemia using ghost cytometry.

Early diagnosis and prompt initiation of appropriate treatment are critical for improving the prognosis of acute leukemia. Acute leukemia is diagnosed by microscopic morphological examination of bone marrow smears and flow cytometric immunophenotyping of bone marrow cells stained with fluorophore-conjugated antibodies. However, these diagnostic processes require trained professionals and are time and resource-intensive. Here, we present a novel diagnostic approach using ghost cytometry, a recently developed high-content flow cytometric approach, which enables machine vision-based, stain-free, high-speed analysis of cells, leveraging their detailed morphological information. We demonstrate that ghost cytometry can detect leukemic cells from the bone marrow cells of patients diagnosed with acute lymphoblastic leukemia and acute myeloid leukemia without relying on biological staining. The approach presented here holds promise as a precise, simple, swift, and cost-effective diagnostic method for acute leukemia in clinical practice.

Sigma-1 receptor maintains ATAD3A as a monomer to inhibit mitochondrial fragmentation at the mitochondria-associated membrane in amyotrophic lateral sclerosis.

Organelle contact sites are multifunctional platforms for maintaining cellular homeostasis. Alternations of the mitochondria-associated membranes (MAM), one of the organelle contact sites where the endoplasmic reticulum (ER) is tethered to the mitochondria, have been involved in the pathogenesis of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). However, the detailed mechanisms through which MAM integrity is disrupted in ALS have not been fully elucidated. Here, we examined whether AAA ATPase domain-containing protein 3A (ATAD3A), a mitochondrial membrane AAA ATPase accumulating at the MAM, is involved in ALS. We found that sigma-1 receptor (σ1R), an ER-resident MAM protein causative for inherited juvenile ALS, required ATAD3A to maintain the MAM. In addition, σ1R retained ATAD3A as a monomer, which is associated with an inhibition of mitochondrial fragmentation. ATAD3A dimerization and mitochondrial fragmentation were significantly induced in σ1R-deficient or SOD1-linked ALS mouse spinal cords. Overall, these observations indicate that MAM induction by σ1R depends on ATAD3A and that σ1R maintains ATAD3A as a monomer to inhibit mitochondrial fragmentation. Our findings suggest that targeting σ1R-ATAD3A axis would be promising for a novel therapeutic strategy to treat mitochondrial dysfunction in neurological disorders, including ALS.

Pooled CRISPR screening of high-content cellular phenotypes using ghost cytometry.

Recent advancements in image-based pooled CRISPR screening have facilitated the mapping of diverse genotype-phenotype associations within mammalian cells. However, the rapid enrichment of cells based on morphological information continues to pose a challenge, constraining the capacity for large-scale gene perturbation screening across diverse high-content cellular phenotypes. In this study, we demonstrate the applicability of multimodal ghost cytometry-based cell sorting, including both fluorescent and label-free high-content phenotypes, for rapid pooled CRISPR screening within vast cell populations. Using the high-content cell sorter operating in fluorescence mode, we successfully executed kinase-specific CRISPR screening targeting genes influencing the nuclear translocation of RelA. Furthermore, using the multiparametric, label-free mode, we performed large-scale screening to identify genes involved in macrophage polarization. Notably, the label-free platform can enrich target phenotypes without requiring invasive staining, preserving untouched cells for downstream assays and expanding the potential for screening cellular phenotypes even when suitable markers are absent.

Label-free enrichment of human pluripotent stem cell-derived early retinal progenitor cells for cell-based regenerative therapies.

Pluripotent stem cell-based therapy for retinal degenerative diseases is a promising approach to restoring visual function. A clinical study using retinal organoid (RO) sheets was recently conducted in patients with retinitis pigmentosa. However, the graft preparation currently requires advanced skills to identify and excise suitable segments from the transplantable area of the limited number of suitable ROs. This remains a challenge for consistent clinical implementations. Herein, we enabled the enrichment of wild-type (non-reporter) retinal progenitor cells (RPCs) from dissociated ROs using a label-free ghost cytometry (LF-GC)-based sorting system, where a machine-based classifier was trained in advance with another RPC reporter line. The sorted cells reproducibly formed retinal spheroids large enough for transplantation and developed mature photoreceptors in the retinal degeneration rats. This method of enriching early RPCs with no specific surface antigens and without any reporters or chemical labeling is promising for robust preparation of graft tissues during cell-based therapy.

Aggresome formation and liquid-liquid phase separation independently induce cytoplasmic aggregation of TAR DNA-binding protein 43.

Cytoplasmic inclusion of TAR DNA-binding protein 43 (TDP-43) is a pathological hallmark of amyotrophic lateral sclerosis (ALS) and a subtype of frontotemporal lobar degeneration (FTLD). Recent studies have suggested that the formation of cytoplasmic TDP-43 aggregates is dependent on a liquid-liquid phase separation (LLPS) mechanism. However, it is unclear whether TDP-43 pathology is induced through a single intracellular mechanism such as LLPS. To identify intracellular mechanisms responsible for TDP-43 aggregation, we established a TDP-43 aggregation screening system using a cultured neuronal cell line stably expressing EGFP-fused TDP-43 and a mammalian expression library of the inherited ALS/FTLD causative genes, and performed a screening. We found that microtubule-related proteins (MRPs) and RNA-binding proteins (RBPs) co-aggregated with TDP-43. MRPs and RBPs sequestered TDP-43 into the cytoplasmic aggregates through distinct mechanisms, such as microtubules and LLPS, respectively. The MRPs-induced TDP-43 aggregates were co-localized with aggresomal markers and dependent on histone deacetylase 6 (HDAC6), suggesting that aggresome formation induced the co-aggregation. However, the MRPs-induced aggregates were not affected by 1,6-hexanediol, an LLPS inhibitor. On the other hand, the RBPs-induced TDP-43 aggregates were sensitive to 1,6-hexanediol, but not dependent on microtubules or HDAC6. In sporadic ALS patients, approximately half of skein-like TDP-43 inclusions were co-localized with HDAC6, but round and granular type inclusion were not. Moreover, HDAC6-positive and HDAC6-negative inclusions were found in the same ALS patient, suggesting that the two distinct pathways are both involved in TDP-43 pathology. Our findings suggest that at least two distinct pathways (i.e., aggresome formation and LLPS) are involved in inducing the TDP-43 pathologies.

ALS-linked TDP-43M337V knock-in mice exhibit splicing deregulation without neurodegeneration.

Abnormal accumulation of TAR DNA-binding protein 43 (TDP-43), a DNA/RNA binding protein, is a pathological signature of amyotrophic lateral sclerosis (ALS). Missense mutations in the TARDBP gene are also found in inherited and sporadic ALS, indicating that dysfunction in TDP-43 is causative for ALS. To model TDP-43-linked ALS in rodents, we generated TDP-43 knock-in mice with inherited ALS patient-derived TDP-43M337V mutation. Homozygous TDP-43M337V mice developed normally without exhibiting detectable motor dysfunction and neurodegeneration. However, splicing of mRNAs regulated by TDP-43 was deregulated in the spinal cords of TDP-43M337V mice. Together with the recently reported TDP-43 knock-in mice with ALS-linked mutations, our finding indicates that ALS patient-derived mutations in the TARDBP gene at a carboxyl-terminal domain of TDP-43 may cause a gain of splicing function by TDP-43, however, were insufficient to induce robust neurodegeneration in mice.

Mice deficient in the C-terminal domain of TAR DNA-binding protein 43 develop age-dependent motor dysfunction associated with impaired Notch1-Akt signaling pathway.

Intracellular mislocalization of TAR DNA-binding protein 43 (TDP-43), a nuclear DNA/RNA-binding protein involved in RNA metabolism, is a pathological hallmark of amyotrophic lateral sclerosis (ALS). Although the aggregation-prone, TDP-43 C-terminal domain is widely considered as a key component of TDP-43 pathology in ALS, recent studies including ours suggest that TDP-43 N-terminal fragments (TDP-∆C) may also contribute to the motor dysfunction in ALS. However, the specific pathological functions of TDP-43 N-terminal fragments in mice have not been elucidated. Here, we established TDP-∆C knock-in mice missing a part of exon 6 of murine Tardbp gene, which encodes the C-terminal region of TDP-43. Homozygous TDP-∆C mice showed embryonic lethality, indicating that the N-terminal domain of TDP-43 alone is not sufficient for normal development. In contrast, heterozygous TDP-∆C mice developed normally but exhibited age-dependent mild motor dysfunction with a loss of C-boutons, large cholinergic synaptic terminals on spinal α-motor neurons. TDP-∆C protein broadly perturbed gene expression in the spinal cords of aged heterozygous TDP-∆C mice, including downregulation of Notch1 mRNA. Moreover, the level of Notch1 mRNA was suppressed both by TDP-43 depletion and TDP-∆C expression in Neuro2a cells. Decreased Notch1 mRNA expression in aged TDP-∆C mice was associated with the age-dependent motor dysfunction and loss of Akt surviving signal. Our findings indicate that the N-terminal region of TDP-43 derived from TDP-∆C induces the age-dependent motor dysfunction associated with impaired Notch1-Akt axis in mice.