Biology subjects

Hatada, I.

Publications and source records attributed to Hatada, I..

6 recordsLinked to original sources

bioRxiv2025

Glucagon dysfunction in the liver induces hyperplasia of PP cells and the production of glucagon and pancreatic polypeptide double-positive cells

Understanding the mechanisms that regulate cellular identity and proliferation is crucial for elucidating cellular functions. Under normal conditions, pancreatic endocrine cells express only a single hormone, and their numbers are tightly regulated. Contrary to this general principle, our study revealed a significant increase in glucagon (GCG) and pancreatic polypeptide (PP) double-positive cells (GCG+ PP+ double-positive cells), along with hyperplasia of both PP and cells in proglucagon-deficient mice. Similarly, systemic glucagon receptor-deficient mice exhibited PP-cell hyperplasia and an increase in GCG+ PP+ double-positive cells, with enhanced PP-cell self-replication observed at 4 weeks and the appearance of GCG+ PP+ double-positive cells at 10 weeks. Liver-specific glucagon receptor-deficient mice induced similar effects, which were linked to hyperaminoacidemia. Elevated glutamine levels were found to promote GCG+ PP+ double-positive cell formation via mTOR signaling, suggesting a molecular mechanism driving pancreatic endocrine cell plasticity. Collectively, these findings indicate that increased plasma amino acid levels caused by impaired glucagon action in the liver promotes the proliferation of cells and PP cells, and disturbs their cellular identity maintenance.

cell biology↗

bioRxiv2024

Descending locus coeruleus noradrenergic signaling to spinal astrocyte subset is required for stress-induced pain facilitation

It is known that stress powerfully alters pain, but its underlying mechanisms remain elusive. Here, we identified a circuit, locus coeruleus descending noradrenergic neurons projecting to the spinal dorsal horn (LC[->]SDH-NA neurons), that is activated by acute exposure to restraint stress and is required for stress-induced mechanical pain hypersensitivity in mice. Interestingly, the primary target of spinal NA released from descending LC[->]SDH-NAergic terminals causing the stress-induced pain hypersensitivity was 1A-adrenaline receptors (1ARs) in Hes5-positive (Hes5+) astrocytes located in the SDH, an astrocyte subset that has an ability to induce pain sensitization. Furthermore, activation of Hes5+ astrocytes reduced activity of SDH-inhibitory neurons (SDH-INs) that have an inhibitory role in pain processing. This astrocytic reduction of IN activity was canceled by an A1-adenosine receptor (A1R)-knockdown in SDH-INs, and the A1R-knockdown suppressed pain hypersensitivity caused by acute restraint stress. Therefore, our findings suggest that LC[->]SDH-NA neuronal signaling to Hes5+ SDH astrocytes and subsequent astrocytic reduction of SDH-IN activity are essential for mechanical pain facilitation caused by stress.

neuroscience↗

bioRxiv2024

Branched-chain amino acid metabolism is a crucial modulator of cellular senescence

Cellular senescence is a complex stress response that results in the permanent arrest of cell proliferation. The accumulation of senescent cells occurs during aging in living organisms, and contributes to tissue dysfunction. Although there are growing lines of evidence that various metabolic changes occur in senescent cells, the link between cellular metabolism and senescence is not yet fully understood. In this study, we demonstrate that alterations in the metabolism of branched-chain amino acids (BCAAs) play a crucial role in establishing cellular senescence. Furthermore, we identified mitochondrial BCAA transamination as a crucial step in this process. Our findings show that various types of cellular stress lead to a reduction in the expression of BCAA aminotransferase 2 (BCAT2), one of the BCAA catabolic enzymes, resulting in decreased catabolism of BCAAs and reduced synthesis of glutamate. The reduction of BCAA catabolites, together with the consequent limitation in glutathione production from glutamate, triggers cellular senescence. Furthermore, we demonstrate that a reduction in BCAT2 levels alone is sufficient to induce cellular senescence, both in cultured cells and in mice. Additionally, our results demonstrate that aging alters BCAA metabolism in both mice and humans. Our findings provide new insights into the metabolic mechanisms underlying cellular senescence, with a particular focus on the role of BCAAs.

cell biology↗

bioRxiv2024

ZIP13 regulates lipid metabolism by changing intracellular iron and zinc balance

Metabolic diseases are caused by a prolonged energy imbalance, and adipose tissue is known to be the main contributor. We previously reported that ZIP13, an Slc39a transporter whose deficiency causes Ehlers-Danlos syndrome spondylocheirodysplastic type 3 associated with lipoatrophy, inhibits the adipocyte browning pathway by modulating intracellular zinc status. The precise mechanisms of how ZIP13 regulates the homeostasis of adipose tissue remain unclear and therefore, we investigated the role of ZIP13 in mature adipocytes using adipocyte-specific Zip13-deficient mice. We herein demonstrate that these mice show accelerated lipolysis and reduced respiratory exchange ratio. In addition, abundance of iron and zinc balance were altered during differentiation in normal adipocytes, whereas iron distribution was substantially affected in Zip13-deficient adipocytes, which downregulated PDE activity and enhanced {beta}-adrenergic receptor signaling pathways. Importantly, we confirmed that ZIP13 could transport both zinc and iron, using the Xenopus oocyte transport system and in silico structural dynamics simulations, and that the defect in iron distribution perturbs proper lipolysis. Together, these results illustrate that ZIP13 acts as a key regulator for lipolysis in adipocytes via the proper use of metals, and that the ZIP13-iron axis plays an important role in regulation of lipid metabolism.

cell biology↗

bioRxiv2024

Induction of NASH and vacuolar structures in the Nwd1-/- mouse liver via SERCA2-dependent endoplasmic reticulum stress

The endoplasmic reticulum (ER) stores Ca2+ and plays crucial roles in protein folding, lipid transfer, and its perturbations trigger an ER stress. In the liver, chronic ER stress is involved in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Previous studies revealed that dysfunction of sarco/endoplasmic reticulum calcium ATPase (SERCA2), a key regulator of Ca2+ transport from the cytosol to the ER, is associated with the induction of ER stress and lipid droplet formation. We previously identified NACHT and WD repeat domain-containing protein 1 (Nwd1), which is localized in the ER and mitochondria. However, the physiological significance of Nwd1 outside the central nervous system remains unclear. In this study, we revealed that Nwd1 knockout mice exhibited pathological manifestations comparable to NASH. Nwd1 interacts with SERCA2 near ER membranes. Nwd1-/- livers exhibited reduced SERCA2 ATPase activity and a smaller Ca2+ pool in the ER, leading to an exacerbated state of ER stress. These findings highlight the importance of SERCA2 activity mediated by Nwd1 in the pathogenesis of NASH. HighlightsO_LINwd1-/- mice exhibited NASH-like liver steatosis. C_LIO_LIElevated ER stress, fibrosis, and pyroptosis were observed in Nwd1-/- livers. C_LIO_LINwd1 interacts with SERCA2, an ER membrane Ca2+ pump. C_LIO_LINwd1-/- livers exhibited reduced SERCA2 activity and smaller Ca2+ pools in the ER. C_LI

molecular biology↗

bioRxiv2023

Fibroblast Nrf2 inhibits profibrotic transcription with Ddx54 and mitigates pathological fibrosis in the mouse heart and kidney

BackgroundTissue fibrosis is a common feature of many organ dysfunctions, such as heart failure and chronic kidney disease. However, no fundamental treatment has been developed. This study aims to identify novel molecular mechanisms for antifibrotic intervention, focusing on fibroblast activation. MethodsWe performed a forward genetic screen using a genome-wide CRISPR library in the context of transforming growth factor {beta} (TGF-{beta})-mediated connective tissue growth factor (CTGF) expression, and used unbiased techniques such as Cleavage Under Targets and Tagmentation (CUT&Tag) and proximity-dependent biotin labeling by TurboID to reveal the detailed molecular mechanisms. ResultsCRISPR library screening identified a number of players in both the canonical Smad pathway and the non-canonical pathway. In addition to the known factors, the Keap1-Nrf2 pathway was identified as a predominant regulator of TGF-{beta}-mediated CTGF expression. Keap1 deletion and consequent Nrf2 activation broadly suppressed profibrotic gene expression, independently of conventional antioxidant effects. CUT&Tag revealed that Nrf2 bound to the proximity of fibrosis-related genes including Ctgf and Fn1. Subsequent individual analysis revealed Smad3 and RNA polymerase II binding to the Nrf2 peak site, which was attenuated by Keap1 deletion. TurboID experiments further discovered that Nrf2 interacts with Ddx54, which acts as a corepressor. Consistently, Keap1 deletion-mediated repression of profibrotic gene expression was reversed by additional Ddx54 deletion. The impact of the Keap1-Nrf2 pathway on pathological fibrosis was examined using tamoxifen-inducible fibroblast-specific Keap1 knockout mice. Pressure overload for 4 weeks robustly induced cardiac hypertrophy, fibrosis and contractile dysfunction. However, deletion of Keap1 in the Postn lineage attenuated these cardiac pathologies. The anti-fibrotic effects of Keap1 deletion were also confirmed in renal fibrosis in the unilateral ureteral obstruction (UUO) model. ConclusionsFibroblast Nrf2 transcriptionally represses fibrosis-related genes in cooperation with the corepressor Ddx54. Fibroblast-specific deletion of Keap1 attenuated pathological fibrosis in pressure overload heart failure and renal fibrosis.

cell biology↗