伊藤 素行

Ischemic stroke (IS) is a pathological condition characterized by the cessation of blood flow due to factors such as thrombosis, inflicting severe damage to the cranial nervous system and resulting in numerous disabilities including memory impairments and hemiplegia. Despite the critical nature of this condition, therapeutic options remain limited, with a pressing challenge being the development of treatments aimed at restoring neurological function. In this study, we leveraged zebrafish, renowned for their exceptional regenerative capabilities, to analyze the pathology of IS and the subsequent recovery process. We induced photothrombosis in the telencephalon utilizing rose bengal and conducted a temporal investigation of changes in cerebral vascular function and learning ability. Our findings revealed that blood flow in young zebrafish was restored approximately 7 days post-IS induction (dpi), with brain function recuperating by 14 dpi. Furthermore, we observed an escalation in the expression of the neural stem marker gene at 3dpi, followed by an upregulation of the differentiated neuron marker at 7 and 14dpi. In the aged IS model, symptoms were exacerbated. While cerebral blood flow was restored in 7 days, similar to young zebrafish, the recovery of learning ability was protracted in aged fish. Moreover, an upregulation of the differentiated neuron marker seen in young fish was not observed in the aged model. Collectively, our analysis of the zebrafish IS model and its comparison with existing rodent models may lay the groundwork for novel IS treatment strategies. Furthermore, the zebrafish IS model may prove beneficial for analyzing the impact of aging on the pathology of IS and the recovery process.

Glycosylation, a post-translational modification, plays a crucial role in proper localization and function of proteins. It is regulated by multiple glycosyltransferases and can be influenced by various factors. Inherited missense mutations in glycosylated proteins such as NOTCH3, Low-density lipoprotein receptor (LDLR), and Amyloid precursor protein (APP) could affect their glycosylation states, leading to cerebral small vessel disease, hypercholesterolemia, and Alzheimer's disease, respectively. Additionally, physiological states and aging-related conditions can affect the expression levels of glycosyltransferases. However, the interplay between mutations in glycosylated proteins and changes in their glycosylation levels remains poorly understood. This mini-review summarizes the effects of glycosylation on transmembrane proteins with pathogenic mutations, including NOTCH3, LDLR, and APP. We highlight the synergistic contributions of missense amino acids in the mutant proteins and alterations in their glycosylation states to their molecular pathogenesis.

Abstract Control of nutrient homeostasis plays a central role in cell proliferation/survival during embryonic development and tumor growth. Activation of the Notch signaling pathway, a major contributor to cell–cell interactions, is a potential mechanism for cell adaptation to nutrient‐poor conditions. Our previous study also demonstrated that during embryogenesis when nutrients such as glutamine and growth factors are potentially maintained at lower levels, Notch signaling suppresses mRNA expression of hexokinase 2 (hk2), which is a glycolysis‐associated gene, in the central nervous system. However, whether and how the genetic regulation of HK2 via Notch signaling contributes to cellular adaptability to nutrient‐poor environments remains unknown. In this study, we performed gene expression analysis using a U87‐MG human glioma cell line and revealed that under conditions where both glutamine and serum were absent, Notch signaling was activated and HK2 expression was downregulated by Notch signaling. We also found that Notch‐mediated HK2 suppression was triggered in a Notch ligand‐selective manner. Furthermore, HK2 was shown to inhibit cell proliferation of U87‐MG gliomas, which might depend on Notch signaling activity. Together, our findings suggest the involvement of Notch‐mediated HK2 suppression in an adaptive mechanism of U87‐MG glioma cells to nutrient‐poor conditions.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a genetic vascular dementia characterized by age-related degeneration of vascular mural cells and accumulation of a NOTCH3 mutant protein. NOTCH3 functions as a signaling receptor, activating downstream gene expression in response to ligands like JAG1 and DLL4, which regulate the development and survival of mural cells. This signal transduction process is thought to be connected with NOTCH3 endocytic degradation. However, the specific cellular circumstances that modulate turnover and signaling efficacy of NOTCH3 mutant protein remain largely unknown. Here, we found elevated NOTCH3 and Radical fringe (RFNG) expression in senescent human pericyte cells. We then investigated impacts of RFNG on glycosylation, degradation, and signal activity of three NOTCH3 CADASIL mutants (R90C, R141C, and C185R) in EGF-like repeat-2, 3, and 4, respectively. Liquid chromatography with tandem mass spectrometry analysis showed that RFNG modified NOTCH3 WT and C185R to different degrees. Additionally, coculture experiments demonstrated that RFNG significantly promoted JAG1-dependent degradation of NOTCH3 WT but not that of R141C and C185R mutants. Furthermore, RFNG exhibited a greater inhibitory effect on JAG1-mediated activity of NOTCH3 R141C and C185R compared to that of NOTCH3 WT and R90C. In summary, our findings suggest that NOTCH3 R141C and C185R mutant proteins are relatively susceptible to accumulation and signaling impairment under cellular conditions of RFNG and JAG1 coexistence.

We have reported that an environmental pollutant, cadmium, promotes cell death in the human renal tubular cells (RTCs) through hyperactivation of a serine/threonine kinase Akt. However, the molecular mechanisms downstream of Akt in this process have not been elucidated. Cadmium has a potential to accumulate misfolded proteins, and proteotoxicity is involved in cadmium toxicity. To clear the roles of Akt in cadmium exposure-induced RTCs death, we investigated the possibility that Akt could regulate proteotoxicity through autophagy in cadmium chloride (CdCl2)-exposed HK-2 human renal proximal tubular cells. CdCl2 exposure promoted the accumulation of misfolded or damaged proteins, the formation of aggresomes (pericentriolar cytoplasmic inclusions), and aggrephagy (selective autophagy to degrade aggresome). Pharmacological inhibition of Akt using MK2206 or Akti-1/2 enhanced aggrephagy by promoting dephosphorylation and nuclear translocation of transcription factor EB (TFEB)/transcription factor E3 (TFE3), lysosomal transcription factors. TFEB or TFE3 knockdown by siRNAs attenuated the protective effects of MK2206 against cadmium toxicity. These results suggested that aberrant activation of Akt attenuates aggrephagy via TFEB or TFE3 to facilitate CdCl2-induced cell death. Furthermore, these roles of Akt/TFEB/TFE3 were conserved in CdCl2-exposed primary human RTCs. The present study shows the molecular mechanisms underlying Akt activation that promotes cadmium-induced RTCs death.