PubMed Health⌕ Search

Biomedical subjects

Naoto Kubota

Publications and source records attributed to Naoto Kubota.

At least 19 recordsLinked to original sources
PubMed2026

Hereditary Diffuse Gastric Cancer With Poorly Differentiated Gallbladder Adenocarcinoma: A Case Report Suggesting Carcinogenesis in the Stomach and Gallbladder Caused by a Pathogenic Germline Variant in CDH1.

BACKGROUND/AIM: Hereditary diffuse gastric cancer (HDGC) is an autosomal dominant cancer syndrome primarily characterized by a high lifetime risk of diffuse gastric cancer and lobular breast cancer. It is predominantly caused by inactivating germline variants in the tumor suppressor gene CDH1. While the association between HDGC and these two specific malignancies is well-established, the co-occurrence of extra-gastric malignancies in other organs remains exceptionally rare. In particular, the clinical and genetic relationship between HDGC and gallbladder adenocarcinoma has not been previously clarified. CASE REPORT: We present the case of a 67-year-old female initially referred for surgical management of gallbladder cancer (GBC) following an initial cholecystectomy for progressive wall thickening. Pathological examination of the gallbladder revealed a de novo, poorly differentiated adenocarcinoma invading the subserosal layer with reduced E-cadherin expression. Given the atypical histopathology and a significant family history-her father and brother both died of gastric cancer at young ages-a preoperative gastric endoscopy was performed. The endoscopy identified multiple faded mucosal lesions, which biopsy confirmed as signet-ring cell carcinoma. The patient subsequently underwent total gastrectomy and gallbladder bed resection. Postoperative pathology identified 22 distinct malignant gastric lesions, predominantly signet-ring cell carcinoma (pT1a), showing variable or lost E-cadherin expression. Germline genetic testing via direct sequencing identified a pathogenic frameshift mutation in exon 5 of the CDH1 gene. CONCLUSION: This represents the first reported case of synchronous HDGC and primary gallbladder adenocarcinoma associated with a germline CDH1 mutation. Our findings suggest that pathogenic CDH1 variants may contribute to the carcinogenesis of poorly differentiated gallbladder adenocarcinoma. Clinicians should consider the possibility of extra-gastric malignancies in HDGC patients.

Humans↗
PubMed2024

The phosphatidylserine targeting antibody bavituximab plus pembrolizumab in unresectable hepatocellular carcinoma: a phase 2 trial.

Immune checkpoint inhibitors targeting PD-1/L1 have modest efficacy in hepatocellular carcinoma as single agents. Targeting membranous phosphatidylserine may induce pro-inflammatory and -immune stimulating effects that enhance immunotherapy activity. This hypothesis was tested in a single-arm phase 2 trial evaluating frontline bavituximab, a phosphatidylserine targeting antibody, plus pembrolizumab (anti-PD-1) in patients with unresectable hepatocellular carcinoma (NCT03519997). The primary endpoint was investigator-assessed objective response rate among evaluable patients, and secondary end points included progression-free survival, incidence of adverse events, overall survival, and duration of response. Among 28 evaluable patients, the confirmed response rate was 32.1%, which met the pre-specified endpoint, and the median progression-free survival was 6.3 months (95% CI, 1.3-11.3 months). Treatment related-adverse events of any grade occurred in 45.7% of patients, with grade 3 or greater adverse events in 14.3% of patients. Adverse events of any cause were observed in 33 patients (94.3%), with grade 3 or greater adverse events in 11 patients (31.4%). Prespecified exploratory analyses of baseline tumor specimens showed that a depletion of B cells, and the presence of fibrotic tissue and expression of immune checkpoints in stroma was associated with tumor response. These results suggest that targeting phosphatidylserine may lead to synergistic effects with PD-1 blockade without increasing toxicity rates, and future studies on this therapeutic strategy may be guided by biomarkers characterizing the pre-treatment tumor microenvironment.

Humans↗
PubMed2007

Glucokinase and IRS-2 are required for compensatory beta cell hyperplasia in response to high-fat diet-induced insulin resistance.

Glucokinase (Gck) functions as a glucose sensor for insulin secretion, and in mice fed standard chow, haploinsufficiency of beta cell-specific Gck (Gck(+/-)) causes impaired insulin secretion to glucose, although the animals have a normal beta cell mass. When fed a high-fat (HF) diet, wild-type mice showed marked beta cell hyperplasia, whereas Gck(+/-) mice demonstrated decreased beta cell replication and insufficient beta cell hyperplasia despite showing a similar degree of insulin resistance. DNA chip analysis revealed decreased insulin receptor substrate 2 (Irs2) expression in HF diet-fed Gck(+/-) mouse islets compared with wild-type islets. Western blot analyses confirmed upregulated Irs2 expression in the islets of HF diet-fed wild-type mice compared with those fed standard chow and reduced expression in HF diet-fed Gck(+/-) mice compared with those of HF diet-fed wild-type mice. HF diet-fed Irs2(+/-) mice failed to show a sufficient increase in beta cell mass, and overexpression of Irs2 in beta cells of HF diet-fed Gck(+/-) mice partially prevented diabetes by increasing beta cell mass. These results suggest that Gck and Irs2 are critical requirements for beta cell hyperplasia to occur in response to HF diet-induced insulin resistance.

Animals↗
PubMed2006

Regulation of bone formation by adiponectin through autocrine/paracrine and endocrine pathways.

Since interaction between bone and lipid metabolism has been suggested, this study investigated the regulation of bone metabolism by adiponectin, a representative adipokine, by analyzing deficient and overexpressing transgenic mice. We initially confirmed that adiponectin and its receptors were expressed in osteoblastic and osteoclastic cells, indicating that adiponectin can act on bone not only through an endocrine pathway as a hormone secreted from fat tissue, but also through an autocrine/paracrine pathway. There was no abnormality in bone mass or turnover of adiponectin-deficient (Ad-/-) mice, possibly due to an equivalent balance of the two pathways. In the culture of bone marrow cells from the Ad-/- mice, osteogenesis was decreased compared to the wild-type (WT) cell culture, indicating a positive effect of endogenous adiponectin through the autocrine/paracrine pathway. To examine the endocrine action of adiponectin, we analyzed transgenic mice overexpressing adiponectin in the liver, and found no abnormality in the bone. Addition of recombinant adiponectin in cultured osteoprogenitor cells suppressed osteogenesis, suggesting that the direct action of circulating adiponectin was negative for bone formation. In the presence of insulin, however, this suppression was blunted, and adiponectin enhanced the insulin-induced phosphorylations of the main downstream molecule insulin receptor substrate-1 and Akt. These lines of results suggest three distinct adiponectin actions on bone formation: a positive action through the autocrine/paracrine pathway by locally produced adiponectin, a negative action through the direct pathway by circulating adiponectin, and a positive action through the indirect pathway by circulating adiponectin via enhancement of the insulin signaling.

Adiponectin↗
PubMed2006

Overexpression of monocyte chemoattractant protein-1 in adipose tissues causes macrophage recruitment and insulin resistance.

Adipose tissue expression and circulating concentrations of monocyte chemoattractant protein-1 (MCP-1) correlate positively with adiposity. To ascertain the roles of MCP-1 overexpression in adipose, we generated transgenic mice by utilizing the adipocyte P2 (aP2) promoter (aP2-MCP-1 mice). These mice had higher plasma MCP-1 concentrations and increased macrophage accumulation in adipose tissues, as confirmed by immunochemical, flow cytometric, and gene expression analyses. Tumor necrosis factor-alpha and interleukin-6 mRNA levels in white adipose tissue and plasma non-esterified fatty acid levels were increased in transgenic mice. aP2-MCP-1 mice showed insulin resistance, suggesting that inflammatory changes in adipose tissues may be involved in the development of insulin resistance. Insulin resistance in aP2-MCP-1 mice was confirmed by hyperinsulinemic euglycemic clamp studies showing that transgenic mice had lower rates of glucose disappearance and higher endogenous glucose production than wild-type mice. Consistent with this, insulin-induced phosphorylations of Akt were significantly decreased in both skeletal muscles and livers of aP2-MCP-1 mice. MCP-1 pretreatment of isolated skeletal muscle blunted insulin-stimulated glucose uptake, which was partially restored by treatment with the MEK inhibitor U0126, suggesting that circulating MCP-1 may contribute to insulin resistance in aP2-MCP-1 mice. We concluded that both paracrine and endocrine effects of MCP-1 may contribute to the development of insulin resistance in aP2-MCP-1 mice.

Adipose Tissue↗
PubMed2006

Peroxisome proliferator-activated receptor gamma-mediated regulation of neural stem cell proliferation and differentiation.

Peroxisome proliferator-activated receptor gamma (PPARgamma) plays an important role in insulin sensitivity, tissue homeostasis, and regulating cellular functions. We found high-level expression of PPARgamma in embryo mouse brain and neural stem cells (NSCs), in contrast to extremely low levels in adult mouse brain. Here, we show that PPARgamma mediates the proliferation and differentiation of murine NSCs via up-regulation of the epidermal growth factor receptor and activation of the ERK pathway. Cell growth rates of NSCs prepared from heterozygous PPARgamma-deficient mouse brains, PPARgamma-RNA-silenced NSCs, and PPARgamma dominant-negative NSCs were significantly decreased compared with those of wild-type NSCs. Physiological concentrations of PPARgamma agonists, rosiglitazone and pioglitazone, stimulated NSC growth, whereas antagonists caused cell death in a concentration-dependent manner via activation of the caspase cascade. The stimulation of cell growth by PPARgamma was associated with a rapid activation of the ERK pathway by phosphorylation and up-regulation of epidermal growth factor receptor and cyclin B protein levels. In contrast, activation of PPARgamma by agonists inhibited the differentiation of NSCs into neurons. The inhibition of differentiation was associated with an activation of STAT3. These data indicate that PPARgamma regulates the development of the central nervous system during early embryogenesis via control of NSC proliferation.

Animals↗
PubMed2006

Pioglitazone ameliorates insulin resistance and diabetes by both adiponectin-dependent and -independent pathways.

Thiazolidinediones have been shown to up-regulate adiponectin expression in white adipose tissue and plasma adiponectin levels, and these up-regulations have been proposed to be a major mechanism of the thiazolidinedione-induced amelioration of insulin resistance linked to obesity. To test this hypothesis, we generated adiponectin knock-out (adipo-/-) ob/ob mice with a C57B/6 background. After 14 days of 10 mg/kg pioglitazone, the insulin resistance and diabetes of ob/ob mice were significantly improved in association with significant up-regulation of serum adiponectin levels. Amelioration of insulin resistance in ob/ob mice was attributed to decreased glucose production and increased AMP-activated protein kinase in the liver but not to increased glucose uptake in skeletal muscle. In contrast, insulin resistance and diabetes were not improved in adipo-/-ob/ob mice. After 14 days of 30 mg/kg pioglitazone, insulin resistance and diabetes of ob/ob mice were again significantly ameliorated, which was attributed not only to decreased glucose production in the liver but also to increased glucose uptake in skeletal muscle. Interestingly, adipo-/-ob/ob mice also displayed significant amelioration of insulin resistance and diabetes, which was attributed to increased glucose uptake in skeletal muscle but not to decreased glucose production in the liver. The serum-free fatty acid and triglyceride levels as well as adipocyte sizes in ob/ob and adipo-/-ob/ob mice were unchanged after 10 mg/kg pioglitazone but were significantly reduced to a similar degree after 30 mg/kg pioglitazone. Moreover, the expressions of TNFalpha and resistin in adipose tissues of ob/ob and adipo-/-ob/ob mice were unchanged after 10 mg/kg pioglitazone but were decreased after 30 mg/kg pioglitazone. Thus, pioglitazone-induced amelioration of insulin resistance and diabetes may occur adiponectin dependently in the liver and adiponectin independently in skeletal muscle.

Adiponectin↗
PubMed2006

Effects of peroxisome proliferator-activated receptor gamma and its ligand on blood-retinal barrier in a streptozotocin-induced diabetic model.

PURPOSE: To clarify whether endogenous peroxisome proliferator-activated receptor gamma (PPARgamma) and its ligand, rosiglitazone, affect retinal leukostasis and the associated vascular leakage using an experimental diabetic model. METHODS: Diabetes was induced in heterozygous PPARgamma+/- mice and Brown Norway rats with an intraperitoneal streptozotocin (STZ) injection. Retinal leukostasis and leakage, quantified by concanavalin A (Con A) lectin perfusion labeling combined with a fluorophotometric dextran leakage assay, were investigated at 120 days in diabetic PPARgamma+/- and wild-type mice and at 21 days in diabetic rats receiving rosiglitazone or the vehicle. The retinal protein expression levels of vascular endothelial growth factor (VEGF), tumor necrosis factor (TNF)-alpha, and the intercellular adhesion molecule (ICAM)-1 were investigated by means of the ELISA assay. RESULTS: In the diabetic PPARgamma+/- mice, retinal leukostasis and leakage were greater than in the diabetic wild-type mice. In addition retinal leukostasis and leakage were suppressed by treatment with rosiglitazone in experimental diabetic rats. ELISA analysis revealed that the upregulated ICAM-1 expression in the diabetic rat retina was reduced by rosiglitazone treatment. CONCLUSIONS: An endogenous pathway involving PPARgamma provides protection against retinal leukostasis and retinal leakage in diabetes and treatment with PPARgamma specific ligands inhibits retinal leukostasis and retinal leakage in diabetic rats.

Animals↗
PubMed2006

Adiponectin and adiponectin receptors in insulin resistance, diabetes, and the metabolic syndrome.

Adiponectin is an adipokine that is specifically and abundantly expressed in adipose tissue and directly sensitizes the body to insulin. Hypoadiponectinemia, caused by interactions of genetic factors such as SNPs in the Adiponectin gene and environmental factors causing obesity, appears to play an important causal role in insulin resistance, type 2 diabetes, and the metabolic syndrome, which are linked to obesity. The adiponectin receptors, AdipoR1 and AdipoR2, which mediate the antidiabetic metabolic actions of adiponectin, have been cloned and are downregulated in obesity-linked insulin resistance. Upregulation of adiponectin is a partial cause of the insulin-sensitizing and antidiabetic actions of thiazolidinediones. Therefore, adiponectin and adiponectin receptors represent potential versatile therapeutic targets to combat obesity-linked diseases characterized by insulin resistance. This Review describes the pathophysiology of adiponectin and adiponectin receptors in insulin resistance, diabetes, and the metabolic syndrome.

Adiponectin↗
PubMed2005

Chemopreventive effect of peroxisome proliferator-activated receptor gamma on gastric carcinogenesis in mice.

Peroxisome proliferator-activated receptor gamma (PPARgamma) is known to be expressed in several cancers, and the treatment of these cancer cells with PPARgamma ligands often induces cell differentiation and apoptosis. Recently, the chemopreventive potential of PPARgamma ligands on colon carcinogenesis was reported, although the effect of PPARgamma on colon carcinogenesis and the mechanism of the effect remain controversial. In this study, we attempted to elucidate the role of PPARgamma in gastric carcinogenesis and explored the possible use of PPARgamma ligand as a chemopreventive agent for gastric cancer. N-methyl-N-nitrosourea (MNU, 240 ppm) was given in drinking water for 10 weeks to induce gastric cancer in PPARgamma wild-type (+/+) and heterozygous-deficient (+/-) mice, followed by treatment with PPARgamma ligand [troglitazone, 0.15% (w/w) in powder food] or the vehicle alone for 42 weeks. At the end of the experiment, PPARgamma (+/-) mice were more susceptible to MNU-induced gastric cancer than wild-type (+/+) mice (89.5%/55.5%), and troglitazone significantly reduced the incidence of gastric cancer in PPARgamma (+/+) mice (treatment 55.5%/vehicle 9%) but not in PPARgamma (+/-) mice. The present study showed that (a) PPARgamma suppresses gastric carcinogenesis, (b) the PPARgamma ligand troglitazone is a potential chemopreventive agent for gastric carcinogenesis, and (c) troglitazone's chemopreventive effect is dependent on PPARgamma.

Animals↗
PubMed2005

Role of Krüppel-like factor 15 (KLF15) in transcriptional regulation of adipogenesis.

Krüppel-like zinc finger transcription factors (KLFs) play diverse roles during cell differentiation and development in mammals. We have now shown by microarray analysis that expression of the KLF15 gene is markedly up-regulated during the differentiation of 3T3-L1 preadipocytes into adipocytes. Inhibition of the function of KLF15, either by expression of a dominant negative mutant or by RNA interference, both reduced the expression of peroxisome proliferator-activated receptor gamma (PPARgamma) and blocked adipogenesis in 3T3-L1 preadipocytes exposed to inducers of adipocyte differentiation. However, the dominant negative mutant of KLF15 did not affect the expression of CCAAT/enhancer-binding protein beta (C/EBPbeta) elicited by inducers of differentiation in 3T3-L1 preadipocytes. In addition, ectopic expression of KLF15 in NIH 3T3 or C2C12 cells triggered both lipid accumulation and the expression of PPARgamma in the presence of inducers of adipocyte differentiation. Ectopic expression of C/EBPbeta, C/EBPdelta, or C/EBPalpha in NIH 3T3 cells also elicited the expression of KLF15 in the presence of inducers of adipocyte differentiation. Moreover, KLF15 and C/EBPalpha acted synergistically to increase the activity of the PPARgamma2 gene promoter in 3T3-L1 adipocytes. Our observations thus demonstrate that KLF15 plays an essential role in adipogenesis in 3T3-L1 cells through its regulation of PPAR gamma expression.

3T3-L1 Cells↗
PubMed2005

Krüppel-like transcription factor KLF5 is a key regulator of adipocyte differentiation.

Krüppel-like factor 5 (KLF5) is a zinc-finger transcription factor known to play a pivotal role in the pathogenesis of cardiovascular disease. Here, we show that neonatal heterozygous KLF5 knockout mice exhibit a marked deficiency in white adipose tissue development, suggesting that KLF5 is also required for adipogenesis. In 3T3-L1 preadipocytes, KLF5 expression was induced at an early stage of differentiation, and this was followed by expression of PPARgamma2. Constitutive overexpression of dominant-negative KLF5 inhibited adipocyte differentiation, whereas overexpression of wild-type KLF5 induced differentiation even without hormonal stimulation. Moreover, embryonic fibroblasts obtained from KLF5+/- mice showed much attenuated adipocyte differentiation, confirming the key role played by KLF5 in adipocyte differentiation. KLF5 expression is induced by C/EBPbeta and delta. KLF5, in turn, acts in concert with C/EBPbeta/delta to activate the PPARgamma2 promoter. This study establishes KLF5 as a key component of the transcription factor network controlling adipocyte differentiation.

3T3-L1 Cells↗
PubMed2004

Expression of DGAT2 in white adipose tissue is regulated by central leptin action.

Acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes catalyze the final step in mammalian triglyceride synthesis, and their functions are considered to be involved in the mechanisms of obesity, insulin resistance, and leptin resistance. Insulin receptor substrate-2 (IRS-2)-deficient mice exhibit obesity-associated with hypertrophic adipocytes and leptin resistance. Screening for transcripts of genes involved in fatty acid and triglyceride synthesis to investigate the mechanism of the hypertrophic change in the adipocytes showed that expression of DGAT2 mRNA was up-regulated in the white adipose tissue (WAT) of Irs2-/- mice, whereas that of DGAT1 was down-regulated. This reciprocal expression of DGAT1 and DGAT2 was also observed in WAT of leptin-deficient ob/ob mice. A high fat diet also resulted in increased DGAT2 and reduced DGAT1 in the WAT of C57BL/6 mice. Induction of adipocyte hypertrophy in vitro up-regulated both DGAT1 and DGAT2 expression in 3T3-L1 cells, suggesting that adipocyte non-autonomous mechanism in vivo is required for the reciprocal changes in expression of DGAT1 and DGAT2. In fact, intracerebroventricular infusion of leptin reduced DGAT2 expression in WAT of Irs2-/- mice and ob/ob mice, independently of DGAT1 expression. We propose the hypothesis that leptin regulates adipocyte size by altering expression patterns of DGAT via central nervous system to determine the levels of triglyceride synthesis.

3T3-L1 Cells↗
PubMed2004

Insulin/Foxo1 pathway regulates expression levels of adiponectin receptors and adiponectin sensitivity.

Adiponectin/Acrp30 is a hormone secreted by adipocytes, which acts as an antidiabetic and antiatherogenic adipokine. We reported previously that AdipoR1 and -R2 serve as receptors for adiponectin and mediate increased fatty acid oxidation and glucose uptake by adiponectin. In the present study, we examined the expression levels and roles of AdipoR1/R2 in several physiological and pathophysiological states such as fasting/refeeding, obesity, and insulin resistance. Here we show that the expression of AdipoR1/R2 in insulin target organs, such as skeletal muscle and liver, is significantly increased in fasted mice and decreased in refed mice. Insulin deficiency induced by streptozotocin increased and insulin replenishment reduced the expression of AdipoR1/R2 in vivo. Thus, the expression of AdipoR1/R2 appears to be inversely correlated with plasma insulin levels in vivo. Interestingly, the incubation of hepatocytes or myocytes with insulin reduced the expression of AdipoR1/R2 via the phosphoinositide 3-kinase/Foxo1-dependent pathway in vitro. Moreover, the expressions of AdipoR1/R2 in ob/ob mice were significantly decreased in skeletal muscle and adipose tissue, which was correlated with decreased adiponectin binding to membrane fractions of skeletal muscle and decreased AMP kinase activation by adiponectin. This adiponectin resistance in turn may play a role in worsening insulin resistance in ob/ob mice. In conclusion, the expression of AdipoR1/R2 appears to be inversely regulated by insulin in physiological and pathophysiological states such as fasting/refeeding, insulin deficiency, and hyper-insulinemia models via the insulin/phosphoinositide 3-kinase/Foxo1 pathway and is correlated with adiponectin sensitivity.

Adenoviridae↗
PubMed2004

A series of maturity onset diabetes of the young, type 2 (MODY2) mouse models generated by a large-scale ENU mutagenesis program.

Mutant mouse models are indispensable tools for clarifying the functions of genes and for elucidating the underlying pathogenic mechanisms of human diseases. Currently, several large-scale mutagenesis projects that employ the chemical mutagen N-ethyl-N-nitrosourea (ENU) are underway worldwide. One specific aim of our ENU mutagenesis project is to generate diabetic mouse models. We screened 9375 animals for dominant traits using a clinical biochemical test and thereby identified 11 mutations in the glucokinase (Gk) gene that were associated with hyperglycemia. GK is a key regulator of insulin secretion in the pancreatic beta-cell. Approximately 190 heterozygous mutations in the human GK gene have been reported to cause maturity onset diabetes of the young, type 2 (MODY2). In addition, five mutations have been reported to cause permanent neonatal diabetes mellitus (PNDM) when present on both alleles. The mutations in our 11 hyperglycemic mutants are located at different positions in Gk. Four have also been found in human MODY2 patients, and another mutant bears its mutation at the same location that is mutated in a PNDM patient. Thus, ENU mutagenesis is effective for developing mouse models for various human genetic diseases, including diabetes mellitus. Some of our Gk mutant lines displayed impaired glucose-responsive insulin secretion and the mutations had different effects on Gk mRNA levels and/or the stability of the GK protein. This collection of Gk mutants will be valuable for understanding GK gene function, for dissecting the function of the enzyme and as models of human MODY2 and PNDM.

Amino Acid Sequence↗