Biology subjects

Morikawa, R.

Publications and source records attributed to Morikawa, R..

6 recordsLinked to original sources

bioRxiv2025

Intestinal fructose metabolism/GLP-1/β-cell axis counteracts hyperglycemia after short-term fructose ingestion

Fructose ingestion increases circulating GLP-1 and insulin, yet the specific contributions of these hormonal responses to glycaemic control remain incompletely defined. We hypothesised that fructose metabolism in intestinal L-cells triggers GLP-1 secretion, which then potentiates insulin secretion and counteracts fructose-induced hyperglycaemia. To test this hypothesis, we systematically characterised metabolic responses across multiple mouse strains after 24 h ad libitum fructose ingestion. In both lean (NSY.B6-a/a) and obese diabetic (NSY.B6-Ay/a) mice, fructose elevated plasma insulin, glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP). The insulin response was preserved in GIP receptor-deficient mice (Gipr-/-) but was abolished in proglucagon-deficient mice (Gcg-/-) by pharmacological GLP-1 receptor antagonism, indicating a requirement for GLP-1, but not GIP. Across strains, fructose-induced insulin response correlated with attenuation of post-fructose glycaemia, consistent with insulin being essential for suppressing fructose-induced hyperglycaemia. To explore the mechanism underlying fructose-induced GLP-1 secretion, we combined ATP-sensitive potassium channel-deficient mice (Kcnj11-/-), GLUTag L-cell line, and metabolic tracing of 13C-labelled fructose in freshly isolated intestinal crypts. These complementary approaches support a model in which fructolysis increases the ATP/ADP ratio in L-cells, closes KATP channels, and stimulates GLP-1 secretion. In obese diabetic mice, increased fructolytic flux and a higher ATP/ADP ratio were associated with elevated GLP-1 levels, further corroborating this model. Collectively, our findings indicate that intestinal fructose metabolism drives GLP-1 secretion required to potentiate insulin secretion, thereby establishing a gut-pancreas axis that counter-regulates fructose-induced hyperglycaemia. KEY POINTS SUMMARYO_LIFructose ingestion acutely increases plasma insulin levels, but the underlying mechanisms and physiological significance remain elusive. C_LIO_LIOur study demonstrates that short-term (24h) fructose ingestion in mice elevates both insulin and glucagon-like peptide 1 (GLP-1) levels in the blood, with the plasma insulin response being GLP-1-dependent. C_LIO_LIWe found that fructose metabolism in intestinal L-cells triggered GLP-1 secretion by increasing the ATP/ADP ratio and closing ATP-sensitive K+ channels (KATP channels). C_LIO_LIThis intestinal fructose metabolism/GLP-1/{beta}-cell axis plays a crucial role in preventing fructose-induced hyperglycaemia, an effect that is compromised in obese diabetic mice. C_LIO_LIThese insights highlight the previously unclear metabolic responses following short-term fructose ingestion and their importance in glucose homeostasis. C_LI 1. ABSTRACT FIGURE LEGENDThis study investigated the hormonal effects of short-term fructose consumption in mice, allowing them ad-lib access to fructose solution for 24 h. Fructose metabolism in intestinal L-cells increases the intracellular ATP/ADP ratio, leading to GLP-1 secretion via KATP channel closure and Ca2+ influx. GLP-1 promotes insulin secretion from pancreatic {beta}-cells. The fructose metabolism/GLP-1/insulin pathway is essential for mitigation of fructose-induced hyperglycaemia. Figures were drawn using BioRender.com.

physiology↗

bioRxiv2025

Rapid water flow navigates long-distance migration of thermophilic bacteria

Bacteria thrive in nearly all environments on Earth, demonstrating remarkable adaptability to physical stimuli, as well as chemicals and light. However, the mechanisms by which bacteria locate and settle in ecological niches optimal for their growth remains poorly understood. Here, we show that Thermus thermophilus, a highly thermophilic non-flagellated species of bacteria, exhibits positive rheotaxis, navigating upstream in unidirectional rapid water flow. Mimicking their natural habitat at 70{degrees}C with a water current under optical microscopy, cells traveled distances up to 1 mm in 30 min, with infrequent directional changes. This long-distance surface migration is driven by type IV pili, facilitating vertical attachment at the cell pole, and shear-induced tilting of the cell body, resulting in alignment of the leading pole toward the direction of water flow. Direct visualization of T4P filaments and their dynamics revealed that rheotaxis is triggered by weakened attachment at the cell pole, regulated by ATPase activity, which was further validated by a mathematical modeling. Flow experiments on 16 bacterial strains and species in the Deinococcus-Thermus phylum revealed that positive rheotaxis is highly conserved among rod-shaped Thermaceae, whereas no rheotactic behavior was observed in spherical-shaped Deinococcus. Our findings suggest that thermophilic bacteria reach their ecological niches by responding to the physical stimulus of rapid water flow, a ubiquitous feature in hot spring environments. This study highlights unforeseen survival strategies, showcasing an evolutionary adaptation to a surface-associated lifestyle where swimming bacteria would otherwise be swept away.

microbiology↗

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↗

bioRxiv2018

Targeting neuronal and glial cell types with synthetic promoter AAVs in mice, non-human primates, and humans

Targeting genes to specific neuronal or glial cell types is valuable both for understanding and for repairing brain circuits. Adeno-associated viral vectors (AAVs) are frequently used for gene delivery, but targeting expression to specific cell types is a challenge. We created a library of 230 AAVs, each with a different synthetic promoter designed using four independent strategies. We show that ~11% of these AAVs specifically target expression to neuronal and glial cell types in the mouse retina, mouse brain, non-human primate retina in vivo, and in the human retina in vitro. We demonstrate applications for recording, stimulation, and molecular characterization, as well as the intersectional and combinatorial labeling of cell types. These resources and approaches allow economic, fast, and efficient cell-type targeting in a variety of species, both for fundamental science and for gene therapy.

neuroscience↗