Biology subjects

Maejima, Y.

Publications and source records attributed to Maejima, Y..

5 recordsLinked to original sources

bioRxiv2024

β-adrenergic blockers increase cAMP and stimulate insulin secretion through a PKA/RYR2/TRPM5 pathway in pancreatic β-cells in vitro

{beta}-adrenergic blockers ({beta}-blockers) are extensively used to inhibit {beta}-adrenoceptor activation and subsequent cAMP production in many cell types. In this study, we characterized the effects of {beta}-blockers on mouse pancreatic {beta}-cells. Unexpectedly, high doses (100 M) of {beta}- blockers (propranolol and bisoprolol) led to a 5-10 fold increase in cAMP levels, enhanced intracellular influx, and stimulated a 2-4 fold increase in glucose-and glimepiride-induced insulin secretion in MIN6-K8 clonal {beta}-cells and isolated mouse pancreatic islets. These effects were observed despite minimal expression of {beta}-adrenoceptors in these cells. Mechanistically, cAMP increase led to ryanodine receptor 2 (RYR2) phosphorylation via protein kinase A (PKA), triggering Ca2+-induced Ca2+ release (CICR). CICR then activates transient receptor potential cation channel subfamily M member 5 (TRPM5), resulting in increased Ca2+ influx via voltage-dependent Ca2+ channels. These effects contradict the conventional understanding of the pharmacology of {beta}-blockers, highlighting the variability in {beta}-blocker actions depending on the experimental context. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/618403v3_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@c9ef31org.highwire.dtl.DTLVardef@176a67aorg.highwire.dtl.DTLVardef@abc69aorg.highwire.dtl.DTLVardef@17ba9d4_HPS_FORMAT_FIGEXP M_FIG C_FIG At high concentrations (> 10 M), the {beta}-adrenergic blocker propranolol paradoxically increased intracellular cAMP levels in pancreatic {beta}-cells. This leads to PKA-induced RYR2 phosphorylation and extracellular Ca2+ influx, leading to CICR from the ER. CICR activated TRPM5, which augmented {beta}-cell electrical activity, extracellular Ca2+ influx, and insulin secretion.

cell biology↗

bioRxiv2024

Pyruvate kinase modulates the link between β-cell fructose metabolism and insulin secretion

2Glucose triggers insulin secretion from pancreatic {beta}-cells through intracellular glucose metabolism, ATP production, and closure of ATP-sensitive K+ channels (KATP channels). Fructose also stimulates insulin secretion, but the underlying mechanisms remain unclear. This study investigated the contribution of phospholipase C (PLC) signaling and fructose metabolism to fructose-stimulated insulin secretion (FSIS) using MIN6-K8 clonal {beta}-cells and mouse islets. Fructose-induced PLC activation, assessed by inositol 1-phosphate accumulation, was reduced in fructose-unresponsive {beta}-cell models, such as diabetic mouse islets and KATP channel-deficient {beta}-cells, suggesting that {beta}-cell fructose responsiveness is primarily determined by PLC signaling. Although FSIS was dependent on KATP channels and Ca2+ influx, the ATP/ADP ratio was unexpectedly lowered by fructose, and suppression of intracellular fructose metabolism hardly affected FSIS. Metabolic flux analysis revealed that the accumulation of fructose 1-phosphate (F1P) suppressed pyruvate kinase (PK) activity, contributing to ATP depletion. Strikingly, a small-molecule PK activator, TEPP-46, antagonized F1P-mediated PK suppression, prevented the drop in the ATP/ADP ratio, and restored FSIS in MIN6-K8 cells, normal mouse islets, and fructose-unresponsive diabetic mouse islets. These findings revealed the metabolic effects of fructose in {beta}-cells and identified PK as a key regulator linking {beta}-cell fructose metabolism and FSIS, thereby providing new insights into the mechanisms of insulin secretion and potential therapeutic targets for fructose-associated metabolic diseases. 1 GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=124 SRC="FIGDIR/small/608033v2_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@11ce1e9org.highwire.dtl.DTLVardef@1339f22org.highwire.dtl.DTLVardef@1493a5org.highwire.dtl.DTLVardef@e97026_HPS_FORMAT_FIGEXP M_FIG C_FIG Left: Fructose-stimulated insulin secretion (FSIS) is driven by sweet taste receptor (STR)-mediated PLC signaling in pancreatic {beta}-cells. Meanwhile, fructose metabolism does not promote FSIS because fructose causes accumulation of fructose 1-phosphate (F1P), which suppresses pyruvate kinase M2 (PKM2), lowering the ATP/ADP ratio. Right: A small-molecule PK activator counteracted F1P-mediated PKM2 inhibition, prevented ATP decrease, and substantially enhanced FSIS in normal and diabetic mouse {beta}-cells. Thus, PK has been identified as a key regulator linking {beta}-cell fructose metabolism and FSIS.

cell biology↗

bioRxiv2024

Sildenafil amplifies calcium influx and insulin secretion in pancreatic β cells

Sildenafil, a phosphodiesterase-5 (PDE5) inhibitor, has been shown to improve insulin sensitivity in animal models and prediabetic patients. However, its other metabolic effects remain poorly investigated. This study examines the impact of sildenafil on insulin secretion in MIN6-K8 mouse clonal {beta} cells. Sildenafil is shown to amplify insulin secretion by enhancing Ca2+ influx, an effect that requires other depolarizing stimuli in MIN6-K8 cells but not in KATP channel-deficient {beta} cells, which are already depolarized. These results indicate that the action of sildenafil is dependent on depolarization and is independent of KATP channels. Furthermore, sildenafil-amplified insulin secretion is not inhibited by nifedipine or PDE5 knockdown. Thus, sildenafil stimulates Ca2+ influx independently of L-type voltage-dependent Ca2+ channels (VDCCs) and PDE5, a mechanism that differs from the known pharmacology of sildenafil and conventional insulin secretory pathways. Our results reposition sildenafil as an insulinotropic agent that can be used as a potential anti-diabetic medicine or a tool to elucidate the molecular mechanism of insulin secretion.

cell biology↗

bioRxiv2023

Chemogenetic activation of target neurons expressing insect Ionotropic Receptors in the mammalian central nervous system by systemic administration of ligand precursors

The IR-mediated neuronal activation (IRNA) technology allows stimulation of neurons in the brain that heterologously-express members of the insect chemosensory IR repertoire in response to their cognate ligands. In the current protocol, a ligand against the complex consisting of IR84a and IR8a subunits, phenylacetic acid (PhAc), is locally injected into a brain region, because of a low efficiency of PhAc for the delivery into the brain across the blood-brain barrier. To circumvent this invasive injection, here we developed a strategy for activation of target neurons in the brain through peripheral administration with a precursor of PhAc, methyl ester of PhAc (PhAcM), which is efficiently transferred into the brain and converted to the mature ligand by endogenous esterase activities. Peripheral administration of with PhAcM activated IR84a/IR8a-expressing neurons in the locus coeruleus of mice and increased the release of neurotransmitters in their nerve terminal regions. (S)-2-phenylpropionic acid ((S)-PhPr) was newly identified as a ligand for IR84a/IR8a, and peripheral administration with the methyl ester of PhPr with the S-configuration [(S)-PhPrM] caused similar effects on the target neurons. In addition, cell-type specific expression of IR84a/IR8a complex in the striatum of rats was unilaterally induced with a viral vector based on the Cre-loxP system. Peripheral administration with PhAcM or (S)-PhPrM stimulated the neurotransmitter release in the ipsilateral terminal regions of the vector-injected striatum, and PhAcM administration resulted in rotational behavior. Finally, we demonstrated that the metabolites of the peripherally administered-radiolabeled (S)-PhPrM accumulated in the IR84a/IR8a-expressing region in the striatum of the vector-injected rats. These results demonstrate that the systemic IRNA technique provides a powerful strategy for remote manipulation of diverse types of target neurons in the mammalian central nervous system.

neuroscience↗

bioRxiv2023

Cardiomyocyte transcriptomic signatures in response to Trypanosoma cruzi infection underpin Chagas cardiomyopathy progression.

Chagas disease can lead to life-threatening cardiac manifestations that occur more frequently in geographic areas more prevalent with the TcI/II circulating genetic strains. To elucidate the differential transcriptomic signatures of the cardiomyocyte resulting from infection with TcI/II or TcVI T. cruzi strains and explore their relationships with pathogenesis, HL-1 rodent cardiomyocytes were infected with TcI/II or TcVI T. cruzi trypomastigotes. RNA was isolated serially post-infection for microarray analysis. Enrichment analyses of differentially expressed genes (fold-change [≥]2 or [≤] 0.5) highlighted the over-represented biological pathways. We found that Oxidative stress-related GO terms, Hypertrophy model, Apoptosis, and MAPK signaling pathways (all with p<0.01) were upregulated. Glutathione and one-carbon metabolism pathway, and Cellular nitrogen compound metabolic process GO term (all with p <0.001) were upregulated exclusively in the cardiomyocytes infected with the TcI/II strains. Upregulation in the oxidative stress-related and hypertrophic responses are shared hallmarks with viral myocarditis, another inflammatory cardiac pathology. Nitrogen metabolism upregulation and Glutathione metabolism imbalance may implicate the relation of nitrosative stress and poor oxygen radicals scavenging in the unique pathophysiology of chagasic cardiomyopathy development. ImportanceChagas disease affects more than 6 million people worldwide. One-third of those chronically infected will develop the life-threatening condition Chagas Cardiomyopathy (CCM). Trypanosoma cruzi (T. cruzi), grouped based on their genetic variability into six discrete typing units (DTU), are associated with DTU-specific clinical phenotypes. The diverse genetic make-up of parasite virulence factors shall evoke unique host defense responses of variable magnitude, collectively affecting the phenotypic expression of CCM. To address this, we performed a transcriptome analysis of cardiomyocytes infected with three different T. cruzi strains each belonging to a different DTU. As a result, we were able to point out dysregulation in nitrogen metabolic processes, Glutathione, and one-carbon metabolism pathways as main features in the host response against cardiomyopathy-prone T. cruzi strains. Further research on these pathways could serve not only in the lookout for progression biomarkers but also in the lead toward the discovery of new therapeutic targets.

cell biology↗