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Biomedical subjects

Keisuke Sekine

Publications and source records attributed to Keisuke Sekine.

9 recordsLinked to original sources

MIF-CD74 axis facilitates MDSC infiltration in the tumor microenvironment of pancreatic ductal adenocarcinoma.

Immune checkpoint inhibitors show insufficient efficacy against pancreatic ductal adenocarcinoma (PDAC). The tumor microenvironment (TME) has a remarkable influence on responsiveness to cancer immunotherapy. The aim of this study was to investigate immunosuppressive characteristics of TME in PDAC tissues. The flow cytometry (FCM) of PDAC surgical specimens revealed that the profile of tumor-infiltrating leukocytes was classified into myeloid cell- and T-cell-dominant subtypes; the myeloid subtype was associated with poorer patient outcomes. Myeloid-derived suppressor cells (MDSCs) showed the highest hazard ratio among various myeloid cell types. Single-cell RNA sequencing and FCM revealed that most MDSCs, but not lymphocytes, in PDAC tissues characteristically express CD74. Macrophage migration inhibitory factor (MIF), a CD74 ligand, was highly expressed in cancer-associated fibroblasts (CAFs) and cancer cells. Spatial transcriptomics demonstrated that the MIF-CD74+ myeloid cell interaction was recognized in CAF-dominant areas in PDAC tissue. CAFs expressing immune suppressor molecules such as MFAP5 and LRRC15 were consistent with MIF+ CAFs. Furthermore, MIF+ CAFs enhanced the migratory activity of MDSCs and promoted MDSC induction and activation. In the murine model, MDSCs were significantly increased in MIF-expressing PDAC tumors, as were CD74+ M-MDSCs per M-MDSC, confirming in vivo interaction between CD74 and MIF. MDSCs play a crucial role in creating an immunosuppressive TME in PDAC; the MIF-CD74 axis drives interactions between MDSCs and CAFs.

Humans↗

Impaired flow-dependent control of vascular tone and remodeling in P2X4-deficient mice.

The structure and function of blood vessels adapt to environmental changes such as physical development and exercise. This phenomenon is based on the ability of the endothelial cells to sense and respond to blood flow; however, the underlying mechanisms remain unclear. Here we show that the ATP-gated P2X4 ion channel, expressed on endothelial cells and encoded by P2rx4 in mice, has a key role in the response of endothelial cells to changes in blood flow. P2rx4(-/-) mice do not have normal endothelial cell responses to flow, such as influx of Ca(2+) and subsequent production of the potent vasodilator nitric oxide (NO). Additionally, vessel dilation induced by acute increases in blood flow is markedly suppressed in P2rx4(-/-) mice. Furthermore, P2rx4(-/-) mice have higher blood pressure and excrete smaller amounts of NO products in their urine than do wild-type mice. Moreover, no adaptive vascular remodeling, that is, a decrease in vessel size in response to a chronic decrease in blood flow, was observed in P2rx4(-/-) mice. Thus, endothelial P2X4 channels are crucial to flow-sensitive mechanisms that regulate blood pressure and vascular remodeling.

Acetylcholine↗

Neuronal leucine-rich repeat protein 4 functions in hippocampus-dependent long-lasting memory.

Neuronal leucine-rich repeat proteins (NLRRs) are type I transmembrane proteins and expressed in neuronal tissues, but their function remains unknown. Here, we describe the identification and characterization of a new member of the NLRR family, NLRR4, and its potential role in long-lasting memory. We generated NLRR4-deficient (NLRR4(-/-)) mice and found that they showed impaired memory retention. In hippocampus-dependent learning tasks, NLRR4(-/-) mice were able to learn and maintain the memories for one day but unable to retain the memories for four days after learning. In contrast, in a hippocampus-independent task, NLRR4(-/-) mice were able to retain the memory normally for at least seven days. These results suggest that NLRR4 plays a key role in hippocampus-dependent long-lasting memory.

Amino Acid Sequence↗

SRC-1 is necessary for skeletal responses to sex hormones in both males and females.

UNLABELLED: We created SRC-1(-/-) mice by mating floxed SRC-1 mice with CMV-Cre transgenic mice. The SRC-1(-/-) mice showed high turnover osteopenia under physiological conditions and hardly responded to osteoanabolic actions of exogenous androgen and estrogen in males and females, respectively, after gonadectomies, indicating that SRC-1 is essential for the maintenance of bone mass by sex hormones. INTRODUCTION: Steroid receptor coactivator-1 (SRC-1) is the first identified coactivator of nuclear receptors. This study investigated the role of SRC-1 in skeletal tissues of males and females using the deficient (SRC-1(-/-)) mice. MATERIALS AND METHODS: SRC-1(-/-) mice were generated by mating our original floxed SRC-1 mice with CMV-Cre transgenic mice. Bone metabolism between 24-week-old SRC-1(-/-) and wildtype (WT) littermates under physiological conditions was compared in males and females by radiological, histological, and biochemical analyses. Difference of skeletal responses to steroid hormones was examined by gonadectomies and exogenous administration experiments with the hormones. Statistical analysis was performed by ANOVA determined by posthoc testing using Bonferroni's method. RESULTS AND CONCLUSIONS: Although SRC-1(-/-) mice showed no abnormality in growth or major organs, both males and females showed osteopenia with high bone turnover in the trabecular bones, but not in the cortical bones, compared with WT littermates. Their serum levels of sex hormones were upregulated, suggesting a compensatory reaction for the insensitivity to these hormones. Gonadectomies caused decreases in BMDs of SRC-1(-/-) and WT mice to the same levels; however, replacement with 5 alpha-dihydrotestosterone and 17 beta-estradiol in males and females, respectively, failed to restore the bone loss in SRC-1(-/-), whereas the WT bone volume was increased to the sham-operated levels. In contrast, bone loss by administered prednisolone was similarly seen in SRC-1(-/-) and WT mice. We conclude that SRC-1 is essential for the maintenance of bone mass by sex hormones, but not for the catabolic action of glucocorticoid, under both physiological and pathological conditions.

Animals↗

Brain masculinization requires androgen receptor function.

Testicular testosterone produced during a critical perinatal period is thought to masculinize and defeminize the male brain from the inherent feminization program and induce male-typical behaviors in the adult. These actions of testosterone appear to be exerted not through its androgenic activity, but rather through its conversion by brain aromatase into estrogen, with the consequent activation of estrogen receptor (ER)-mediated signaling. Thus, the role of androgen receptor (AR) in perinatal brain masculinization underlying the expression of male-typical behaviors remains unclear because of the conversion of testosterone into estrogen in the brain. Here, we report a null AR mutation in mice generated by the Cre-loxP system. The AR-null mutation in males (AR(L-/Y)) resulted in the ablation of male-typical sexual and aggressive behaviors, whereas female AR-null homozygote (AR(L-/L-)) mice exhibited normal female sexual behaviors. Treatment with nonaromatizable androgen (5alpha-dihydrotestosterone, DHT) was ineffective in restoring the impaired male sexual behaviors, but it partially rescued impaired male aggressive behaviors in AR(L-/Y) mice. Impaired male-typical behaviors in ERalpha(-/-) mice were restored on DHT treatment. The role of AR function in brain masculinization at a limited perinatal stage was studied in AR(L-/L-) mice. Perinatal DHT treatment of females led to adult females sensitive to both 17beta-estradiol and DHT in the induction of male-typical behaviors. However, this female brain masculinization was abolished by AR inactivation. Our results suggested that perinatal brain masculinization requires AR function and that expression of male-typical behaviors in adults is mediated by both AR-dependent and -independent androgen signaling.

Androgen Receptor Antagonists↗

Suppressive function of androgen receptor in bone resorption.

As locally converted estrogen from testicular testosterone contributes to apparent androgen activity, the physiological significance of androgen receptor (AR) function in the beneficial effects of androgens on skeletal tissues has remained unclear. We show here that inactivation of AR in mice using a Cre-loxP system-mediated gene-targeting technique caused bone loss in males but not in females. Histomorphometric analyses of 8-week-old male AR knockout (ARKO) mice showed high bone turnover with increased bone resorption that resulted in reduced trabecular and cortical bone mass without affecting bone shape. Bone loss in orchidectomized male ARKO mice was only partially prevented by treatment with aromatizable testosterone. Analysis of primary osteoblasts and osteoclasts from ARKO mice revealed that AR function was required for the suppressive effects of androgens on osteoclastogenesis supporting activity of osteoblasts but not on osteoclasts. Furthermore, expression of the receptor activator of NF-kappaB ligand (RANKL) gene, which encodes a major osteoclastogenesis inducer, was found to be up-regulated in osteoblasts from AR-deficient mice. Our results indicate that AR function is indispensable for male-type bone formation and remodeling.

Androgen-Insensitivity Syndrome↗

FGF10 maintains stem cell compartment in developing mouse incisors.

Mouse incisors are regenerative tissues that grow continuously throughout life. The renewal of dental epithelium-producing enamel matrix and/or induction of dentin formation by mesenchymal cells is performed by stem cells that reside in cervical loop of the incisor apex. However, little is known about the mechanisms of stem cell compartment formation. Recently, a mouse incisor was used as a model to show that fibroblast growth factor (FGF) 10 regulates mitogenesis and fate decision of adult stem cells. To further illustrate the role of FGF10 in the formation of the stem cell compartment during tooth organogenesis, we have analyzed incisor development in Fgf10-deficient mice and have examined the effects of neutralizing anti-FGF10 antibody on the developing incisors in organ cultures. The incisor germs of FGF10-null mice proceeded to cap stage normally. However, at a later stage, the cervical loop was not formed. We found that the absence of the cervical loop was due to a divergence in Fgf10 and Fgf3 expression patterns at E16. Furthermore, we estimated the growth of dental epithelium from incisor explants of FGF10-null mice by organ culture. The dental epithelium of FGF10-null mice showed limited growth, although the epithelium of wild-type mice appeared to grow normally. In other experiments, a functional disorder of FGF10, caused by a neutralizing anti-FGF10 antibody, induced apoptosis in the cervical loop of developing mouse incisor cultures. However, recombinant human FGF10 protein rescued the cervical loop from apoptosis. Taken together, these results suggest that FGF10 is a survival factor that maintains the stem cell population in developing incisor germs.

Animals↗