Argonaute3-SF3B3 complex controls pre-mRNA splicing to restrain type 2 immunity.

Argonaute (AGO) proteins execute microRNA (miRNA)-mediated gene silencing. However, it is unclear whether all 4 mammalian AGO proteins (AGO1, AGO2, AGO3, and AGO4) are required for miRNA activity. We generate Ago1, Ago3, and Ago4-deficient mice (Ago134Δ) and find AGO1/3/4 to be redundant for miRNA biogenesis, homeostasis, or function, a role that is carried out by AGO2. Instead, AGO1/3/4 regulate the expansion of type 2 immunity via precursor mRNA splicing in CD4+ T helper (Th) lymphocytes. Gain- and loss-of-function experiments demonstrate that nuclear AGO3 interacts directly with SF3B3, a component of the U2 spliceosome complex, to aid global mRNA splicing, and in particular the isoforms of the gene Nisch, resulting in a dysregulated Nisch isoform ratio. This work uncouples AGO1, AGO3, and AGO4 from miRNA-mediated RNA interference, identifies an AGO3:SF3B3 complex in the nucleus, and reveals a mechanism by which AGO proteins regulate inflammatory diseases.

Nischarin Deletion Reduces Oxidative Metabolism and Overall ATP: A Study Using a Novel NISCHΔ5-6 Knockout Mouse Model.

Nischarin (Nisch) is a cytosolic scaffolding protein that harbors tumor-suppressor-like characteristics. Previous studies have shown that Nisch functions as a scaffolding protein and regulates multiple biological activities. In the current study, we prepared a complete Nisch knockout model, for the first time, by deletion of exons 5 and 6. This knockout model was confirmed by Qrt-PCR and Western blotting with products from mouse embryonic fibroblast (MEF) cells. Embryos and adult mice of knockouts are significantly smaller than their wild-type counterparts. Deletion of Nisch enhanced cell migration, as demonstrated by wound type and transwell migration assays. Since the animals were small in size, we investigated Nisch's effect on metabolism by conducting several assays using the Seahorse analyzer system. These data indicate that Nisch null cells have lower oxygen consumption rates, lower ATP production, and lower levels of proton leak. We examined the expression of 15 genes involved in lipid and fat metabolism, as well as cell growth, and noted a significant increase in expression for many genes in Nischarin null animals. In summary, our results show that Nischarin plays an important physiological role in metabolic homeostasis.

Prenatal exposure to di (2-ethylhexyl) phthalate causes autism-like behavior through inducing Nischarin expression in the mouse offspring.

Epidemiologic evidence has suggested a relationship between di (2-ethylhexyl) phthalate (DEHP) prenatal exposure and autism spectrum disorders (ASD), but the underlying mechanisms are still at large unknown. In this study, pregnant mice were intragastrically administered with DEHP once a day from GD 3 to GD 17 and the neurobehavioral changes of offspring were evaluated. In addition to the repetitive stereotyped behaviors, DEHP at the concentration of 50 mg/kg/day and above significantly impaired the sociability of the offspring (P < 0.05) and decreased the density of dendritic spines of pyramidal neurons in the prefrontal cortex (P < 0.05). At the same time, the expression of Nischarin protein in prefrontal lobe increased (P < 0.05). Similarly, after 12-h incubation of DEHP at the concentration of 100 nM, the total spine density, especially the mushroom and stubby spine populations, significantly decreased in the primary cultured prefrontal cortical neurons (P < 0.05). However, the inhibitory effect of DEHP were reversed by knockdown of Nischarin expression. Collectively, these results suggest that prenatal DEHP exposure induces Nischarin expression, causes dendritic spine loss, and finally leads to autism-like behavior in mouse offspring.

Small Molecule Targets TMED9 and Promotes Lysosomal Degradation to Reverse Proteinopathy.

Intracellular accumulation of misfolded proteins causes toxic proteinopathies, diseases without targeted therapies. Mucin 1 kidney disease (MKD) results from a frameshift mutation in the MUC1 gene (MUC1-fs). Here, we show that MKD is a toxic proteinopathy. Intracellular MUC1-fs accumulation activated the ATF6 unfolded protein response (UPR) branch. We identified BRD4780, a small molecule that clears MUC1-fs from patient cells, from kidneys of knockin mice and from patient kidney organoids. MUC1-fs is trapped in TMED9 cargo receptor-containing vesicles of the early secretory pathway. BRD4780 binds TMED9, releases MUC1-fs, and re-routes it for lysosomal degradation, an effect phenocopied by TMED9 deletion. Our findings reveal BRD4780 as a promising lead for the treatment of MKD and other toxic proteinopathies. Generally, we elucidate a novel mechanism for the entrapment of misfolded proteins by cargo receptors and a strategy for their release and anterograde trafficking to the lysosome.

Nischarin Regulates Secretion of Exosomes and Cancer Progression.

The intercellular exchange of exosomes may play a regulatory function in tumor progression and metastasis. Maziveyi and colleagues demonstrated that Nischarin regulated the secretion of exosomes from breast cancer cells. Loss of Nischarin expression increased exosome production and promoted tumor cell growth and migration, supporting that Nischarin can influence the behavior of surrounding cancer cells. This study identified a novel function of the tumor suppressor Nischarin in exosome biology and cancer progression.See related article by Maziveyi et al., p. 2152.

The role of IRAS/Nischarin involved in the development of morphine tolerance and physical dependence.

Morphine is a potent opioid analgesic used to alleviate moderate or severe pain, but the development of drug tolerance and dependence limits its use in pain management. Our previous studies showed that the candidate protein for I1 imidazoline receptor, imidazoline receptor antisera-selected (IRAS)/Nischarin, interacts with µ opioid receptor (MOR) and modulates its trafficking. However, there is no report of the effect of IRAS on morphine tolerance and physical dependence. In the present study, we found that IRAS knockout (KO) mice showed exacerbated analgesic tolerance and physical dependence compared to wild-type (WT) mice by chronic morphine treatment. Chronic morphine treatment down-regulated the expression of MOR in spinal cord of IRAS KO mice, while had no significant effect on MOR expression in WT mice. We observed the compensatory increase of cAMP accumulation in spinal cord after morphine tolerance, and this change was more significant in KO mice than WT mice. Furthermore, KO mice showed more elevation in the phosphorylation of AMPA receptor GluR1-S845 than WT mice, while the total expression of GluR1 remained unchanged after morphine dependence. Altogether, these data suggest that IRAS may play an important role in the development of morphine tolerance and physical dependence in vivo through modulating MOR expression, as well as AMPA GluR1-S845 phosphorylation, which might be one of the mechanisms underlying the development of opiate addiction.

Development of insulin resistance in Nischarin mutant female mice.

BACKGROUND/OBJECTIVES: NISCH-STAB1 is a newly identified locus correlated to human waist-hip ratio (WHR), which is a risk indicator of developing obesity-associated diabetes. Our previous studies have shown that Nisch mutant male mice increased glucose tolerance in chow-fed conditions. Thus we hypothesized that Nisch mutant mice will have changes in insulin resistance, adipocytes, hepatic steatosis when mice are fed with high-fat diet (HFD). METHODS: Insulin resistance was assessed in Nisch mutant mice and WT mice fed with high-fat diet (60% by kCal) or chow diet. Whole-body energy metabolism was examined using an indirect calorimeter. Adipose depots including inguinal white adipose tissue (WAT), perigonadal WAT, retroperitoneal WAT, and mesenteric WAT were extracted. Area and eqdiameter of each adipocyte were determined, and insulin signaling was examined as well. Paired samples of subcutaneous and omental visceral adipose tissue were obtained from 400 individuals (267 women, 133 men), and examined the expression of Nischarin. RESULTS: We found that insulin signaling was impaired in major insulin-sensitive tissues of Nisch mutant female mice. When mice were fed with HFD for 15 weeks, the Nisch mutant female mice not only developed severe insulin resistance and decreased glucose tolerance compared with wild-type control mice, but also accumulated more white fat, had larger adipocytes and developed severe hepatic steatosis than wild-type control mice. To link our animal studies to human diseases, we further analyzed Nischarin expression in the paired human samples of visceral and subcutaneous adipose tissue from Caucasians. In humans, we found that Nischarin expression is attenuated in adipose tissue with obesity. More importantly, we found that Nischarin mRNA inversely correlated with parameters of obesity, fat distribution, lipid and glucose metabolism. CONCLUSIONS: Taken together, our data revealed sexual dimorphism of Nischarin in body fat distribution, insulin resistance, and glucose tolerance in mice.

Activation of imidazoline receptor I2, and improved pancreatic ß-cell function in human islets.

AIM: The impact of BL11282, an imidazoline receptor (NISCH) agonist, on potentiation of glucose-stimulated insulin secretion (GSIS) from isolated human non-diabetic (ND) and type 2 diabetic (T2D) islets was investigated. METHODS: Analysis of mRNA was performed by RNA-sequencing and qPCR. Insulin and cAMP by RIA and ELISA respectively. RESULTS: RNA-sequencing data revealed that NISCH is highly expressed in fat tissues, islets, liver and muscles, with eight detectable splice variants of transcripts in islets. NISCH had a positive correlation with GLP-1 (GLP1R) and GIP (GIPR) receptor transcripts. The expression of NISCH was confirmed by qPCR in human islets. NISCH and GLP1R were comparably higher expressed in mouse islets compared to human islets. GSIS was dose-dependently potentiated by BL11282 from incubated islets of ND and T2D human islet donors. The insulinotropic action of BL11282 was associated with increased cAMP. While the harmful effect of high glucose on reductive capacity of islet cells was enhanced by glibenclamide during long-term culture, it was counteracted by BL11282 or Bt2-cAMP. BL11282 also increased proliferation of INS-1 cells during long-time culture. CONCLUSION: Our data suggest that BL11282 potentiates GSIS by an action involving cAMP/PKA system and BL11282 could be an attractive insulinotropic and ß-cell protective agent.

Nischarin regulates focal adhesion and Invadopodia formation in breast cancer cells.

BACKGROUND: During metastasis, tumor cells move through the tracks of extracellular matrix (ECM). Focal adhesions (FAs) are the protein complexes that link the cell cytoskeleton to the ECM and their presence is necessary for cell attachment. The tumor suppressor Nischarin interacts with a number of signaling proteins such as Integrin α5, PAK1, LIMK1, LKB1, and Rac1 to prevent cancer cell migration. Although previous findings have shown that Nischarin exerts this migratory inhibition by interacting with other proteins, the effects of these interactions on the entire FA machinery are unknown. METHODS: RT-PCR, Western Blotting, invadopodia assays, and immunofluorescence were used to examine FA gene expression and determine whether Nischarin affects cell attachment, as well as the proteins that regulate it. RESULTS: Our data show that Nischarin prevents cell migration and invasion by altering the expression of key focal adhesion proteins. Furthermore, we have found that Nischarin-expressing cells have reduced ability to attach the ECM, which in turn leads to a decrease in invadopodia-mediated matrix degradation. CONCLUSIONS: These experiments demonstrate an important role of Nischarin in regulating cell attachment, which adds to our understanding of the early events of the metastatic process in breast cancer.

A mouse-to-man candidate gene study identifies association of chronic otitis media with the loci TGIF1 and FBXO11.

Chronic otitis media with effusion (COME) is the most common cause of hearing loss in children, and known to have high heritability. Mutant mouse models have identified Fbxo11, Evi1, Tgif1, and Nisch as potential risk loci. We recruited children aged 10 and under undergoing surgical treatment for COME from 35 hospitals in the UK, and their nuclear family. We performed association testing with the loci FBXO11, EVI1, TGIF1 and NISCH and sought to replicate significant results in a case-control cohort from Finland. We tested 1296 families (3828 individuals), and found strength of association with the T allele at rs881835 (p = 0.006, OR 1.39) and the G allele at rs1962914 (p = 0.007, OR 1.58) at TGIF1, and the A allele at rs10490302 (p = 0.016, OR 1.17) and the G allele at rs2537742 (p = 0.038, OR 1.16) at FBXO11. Results were not replicated. This study supports smaller studies that have also suggested association of otitis media with polymorphism at FBX011, but this is the first study to report association with the locus TGIF1. Both FBX011 and TGIF1 are involved in TGF-ß signalling, suggesting this pathway may be important in the transition from acute to chronic middle ear inflammation, and a potential molecular target.

Investigation of morin-induced insulin secretion in cultured pancreatic cells.

Morin is a flavonoid contained in guava that is known to reduce hyperglycemia in diabetes. Insulin secretion has been demonstrated to increase following the administration of morin. The present study is designed to investigate the potential mechanism(s) of morin-induced insulin secretion in the MIN6 cell line. First, we identified that morin induced a dose-dependent increase in insulin secretion and intracellular calcium content in MIN6 cells. Morin potentiated glucose-stimulated insulin secretion (GSIS). Additionally, we used siRNA for the ablation of imidazoline receptor protein (NISCH) expression in MIN6 cells. Interestingly, the effects of increased insulin secretion by morin and canavanine were markedly reduced in Si-NISCH cells. Moreover, we used KU14R to block imidazoline I3 receptor (I-3R) that is known to enhance insulin release from the pancreatic ß-cells. Without influence on the basal insulin secretion, KU14R dose-dependently inhibited the increased insulin secretion induced by morin or efaroxan in MIN6 cells. Additionally, effects of increased insulin secretion by morin or efaroxan were reduced by diazoxide at the dose sufficient to open KATP channels and attenuated by nifedipine at the dose used to inhibit L-type calcium channels. Otherwise, phospholipase C (PLC) is introduced to couple with imidazoline receptor (I-R). The PLC inhibitor dose-dependently inhibited the effects of morin in MIN6 cells. Similar blockade was also observed in protein kinase C (PKC) inhibitor-treated cells. Taken together, we found that morin increases insulin secretion via the activation of I-R in pancreatic cells. Therefore, morin would be useful to develop in the research and treatment of diabetic disorders.

Diosmin, a Citrus Nutrient, Activates Imidazoline Receptors to Alleviate Blood Glucose and Lipids in Type 1-Like Diabetic Rats.

Diosmin is a nutrient that is widely contained in citrus and that has been indicated to improve glucose metabolism in diabetic disorders. Recently, we demonstrated that diosmin induces ß-endorphin to lower hyperglycemia in diabetic rats. However, the mechanisms of diosmin in opioid secretion were unclear. Therefore, we focused on the secretion of opioids from isolated adrenal glands induced by diosmin. The changes in the released ß-endorphin-like immunoreactivity (BER) were determined using ELISA. Diosmin increased the BER level in a dose-dependent manner, and this effect was markedly reduced in the absence of calcium ions. Activation of the imidazoline I-2 receptor (I-2R) has been introduced to induce opioid secretion. Interestingly, we observed that diosmin activates CHO cells expressing I-R. Additionally, diosmin-increased BER was inhibited by the blockade of I-2R in isolated adrenal glands. Additionally, an antagonist of I-2R blocked diosmin-induced effects, including the reduction in hyperglycemia and the increase in plasma BER in streptozotocin-induced diabetic rats (STZ-diabetic rats). Repeated treatment of STZ-diabetic rats with diosmin for one week induced changes in hepatic glycogen, lipid levels, and the expression of phosphoenolpyruvate carboxykinase (PEPCK). Furthermore, an antagonist of I-2R blocked the diosmin-induced changes. Additionally, plasma lipids modified by diosmin were also reversed by the blockade of I-2R in STZ-diabetic rats. Taken together, we suggest that diosmin may activate I-2R to enhance the secretion of ß-endorphin from adrenal glands and to influence metabolic homeostasis, resulting in alleviation of blood glucose and lipids in STZ-diabetic rats.

Breast Cancer Tumor Suppressors: A Special Emphasis on Novel Protein Nischarin.

Tumor suppressor genes regulate cell growth and prevent spontaneous proliferation that could lead to aberrant tissue function. Deletions and mutations of these genes typically lead to progression through the cell-cycle checkpoints, as well as increased cell migration. Studies of these proteins are important as they may provide potential treatments for breast cancers. In this review, we discuss a comprehensive overview on Nischarin, a novel protein discovered by our laboratory. Nischarin, or imidazoline receptor antisera-selected protein, is a protein involved in a vast number of cellular processes, including neuronal protection and hypotension. The NISCH promoter experiences hypermethylation in several cancers, whereas some highly aggressive breast cancer cells exhibit genomic loss of the NISCH locus. Furthermore, we discuss data illustrating a novel role of Nischarin as a tumor suppressor in breast cancer. Analysis of this new paradigm may shed light on various clinical questions. Finally, the therapeutic potential of Nischarin is discussed.

Frequent Loss of NISCH Promotes Tumor Proliferation and Invasion in Ovarian Cancer via Inhibiting the FAK Signal Pathway.

NISCH encodes the imidazoline receptor Nischarin and is a known tumor suppressor in many human malignancies; however, its roles in ovarian cancer are still largely unknown. Here, we aim to investigate the biologic functions of NISCH in ovarian cancer. We found that NISCH was significantly downregulated, which correlated considerably with advanced tumor stage, poor differentiation, lymph node metastasis, and the serous/mucinous subtypes in a panel of ovarian cancer tissues. Moreover, NISCH gene silencing was mainly the product of promoter hypermethylation, which could be reversed by treatment with 5-aza-dC. In vitro, NISCH overexpression suppressed cell proliferation and colony formation by hindering cell-cycle progression, whereas the opposite was observed in NISCH knockdown counterparts. In vivo, abundant NISCH expression hindered the growth of HO8910 xenografts, whereas NISCH knockdown accelerated the growth of SKOV3 xenografts. In addition, NISCH significantly attenuated cell invasion by inhibiting the phosphorylation of FAK and ERK, which could be neutralized by PF-562271 (a FAK/Pyk2 inhibitor). Accordingly, NISCH knockdown xenografts exhibited increased peritoneal/pelvic metastases that were not present in counterparts treated with PF-562271. Furthermore, NISCH expression in primary ovarian cancer cells predicted a cellular resistance to PF-562271. In conclusion, we showed that NISCH was frequently silenced by promoter hypermethylation in human ovarian cancer. NISCH manipulated cellular proliferation and invasion by arresting cell cycle and inhibiting the FAK signal. Our findings revealed the biologic functions of NISCH in ovarian cancer, and might be useful for treating patients with aberrant expression of NISCH.

Expression of integrin-binding protein Nischarin in metastatic breast cancer.

The present study aimed to investigate the expression of Nischarin protein in primary breast cancer (PBC), and to evaluate its role in tumor metastasis. Paired specimens of breast cancer tissues and adjacent normal tissues were surgically obtained from 60 patients with PBC at the Zhejiang Cancer Hospital (Hangzhou, China). Nischarin protein concentrations were determined by an ELISA assay. Breast cancer tissues exhibited a significantly lower concentration of Nischarin (5.86 ± 3.19 ng/ml) compared with that of the adjacent noncancerous tissues (9.25 ± 3.65 ng/ml; P<0.001). Furthermore, cancer tissue from patients with lymph node metastasis had significantly lower levels of Nischarin protein (4.69 ± 2.40 ng/ml) than those of patients without lymph node metastasis (7.04 ± 3.47 ng/ml; P=0.004). There was no significant difference in Nischarin protein expression levels between patients with grade I, II or III PBC (grade I, 5.44 ± 3.57 ng/ml; grade II, 6.42 ± 3.85 ng/ml and grade III, 5.10 ± 1.18 ng/ml; P=0.765). The significant differences in the expression of Nischarin between: i) Cancer tissue and noncancerous tissue and ii) patients with and without lymph node metastasis, suggested that Nischarin may have a significant role in tumor occurrence and metastasis of breast cancer. Nischarin expression may therefore be used as a marker to predict the invasiveness and metastasis of PBC.

Integrin-binding protein nischarin interacts with tumor suppressor liver kinase B1 (LKB1) to regulate cell migration of breast epithelial cells.

Biallelic inactivation of LKB1, a serine/threonine kinase, has been detected in 30% of lung adenocarcinomas, and inhibition of breast tumor growth has been demonstrated. We have identified the tumor suppressor, Nischarin, as a novel binding partner of LKB1. Our mapping analysis shows that the N terminus of Nischarin interacts with amino acids 44-436 of LKB1. Time lapse microscopy and Transwell migration data show that the absence of both Nischarin and LKB1 from an invasive breast cancer cell line (MDA-MB-231) enhances migration as measured by increased distance and speed of migrating cells. Our data suggest that this is a result of elevated PAK1 and LIMK1 phosphorylation. Moreover, the absence of Nischarin and LKB1 increased tumor growth in vivo. Consistent with this, the percentage of S phase cells was increased, as demonstrated by flow cytometry and enhanced cyclin D1. The absence of Nischarin and LKB1 also led to a dramatic increase in the formation of lung metastases. Our studies, for the first time, demonstrate functional interaction between LKB1 and Nischarin to inhibit cell migration and breast tumor progression. Mechanistically, we show that these two proteins together regulate PAK-LIMK-Cofilin and cyclin D1/CDK4 pathways.

Improvement of obesity by activation of I1-imidazoline receptors in high fat diet-fed mice.

Imidazoline I1-receptor (I1R) is known to regulate the blood pressure, and rilmenidine, as the agonist, is used to treat hypertension in clinics. However, the role of I1R in obesity is still unclear. In the present study, we investigated the changes of obesity by activation of I1R in high fat diet (HFD)-fed mice. Chronic administration of rilmenidine into HFD-fed mice for 8 weeks significantly reduced body weight, which was reversed by efaroxan at the dose sufficient to block I1R. Also, rilmenidine significantly decreased the energy intake of HFD-fed mice. This reduction of energy intake was abolished by efaroxan at the same dosing for blockade of I1R. However, hypothalamic I1R protein expression in HFD-fed mice was markedly lower than that in normal chow-fed mice. In addition, epididymal white adipose tissue (eWAT) cell size in HFD-fed mice was decreased by rilmenidine via the activation of I1R. Moreover, effect of rilmenidine on appetite disappeared in db/db mice. Taken together, we suggest that rilmenidine can improve obesity in HFD-fed mice through an activation of I1R to ameliorate energy intake and eWAT accumulation.

Cigarette smoke induces methylation of the tumor suppressor gene NISCH.

We have previously identified a putative tumor suppressor gene, NISCH, whose promoter is methylated in lung tumor tissue as well as in plasma obtained from lung cancer patients. NISCH was observed to be more frequently methylated in smoker lung cancer patients than in non-smoker lung cancer patients. Here, we investigated the effect of tobacco smoke exposure on methylation of the NISCH gene. We tested methylation of NISCH after oral keratinocytes were exposed to mainstream and side stream cigarette smoke extract in culture. Methylation of the promoter region of the NISCH gene was also evaluated in plasma obtained from lifetime non-smokers and light smokers (<20 pack/year), with and without lung tumors, and heavy smokers (20+ pack/year) without disease. Promoter methylation of NISCH was tested by quantitative fluorogenic real-time PCR in all samples. Promoter methylation of NISCH occurred after exposure to mainstream tobacco smoke as well as to side stream tobacco smoke in normal oral keratinocyte cell lines. NISCH methylation was also detected in 68% of high-risk, heavy smokers without detectable tumors. Interestingly, in light smokers, NISCH methylation was present in 69% of patients with lung cancer and absent in those without disease. Our pilot study indicates that tobacco smoke induces methylation changes in the NISCH gene promoter before any detectable cancer. Methylation of the NISCH gene was also found in lung cancer patients' plasma samples. After confirming these findings in longitudinally collected plasma samples from high-risk populations (such as heavy smokers), examining patients for hypermethylation of the NISCH gene may aid in identifying those who should undergo additional screening for lung cancer.

Rac and Rab GTPases dual effector Nischarin regulates vesicle maturation to facilitate survival of intracellular bacteria.

The intracellular pathogenic bacterium Salmonella enterica serovar typhimurium (Salmonella) relies on acidification of the Salmonella-containing vacuole (SCV) for survival inside host cells. The transport and fusion of membrane-bound compartments in a cell is regulated by small GTPases, including Rac and members of the Rab GTPase family, and their effector proteins. However, the role of these components in survival of intracellular pathogens is not completely understood. Here, we identify Nischarin as a novel dual effector that can interact with members of Rac and Rab GTPase (Rab4, Rab14 and Rab9) families at different endosomal compartments. Nischarin interacts with GTP-bound Rab14 and PI(3)P to direct the maturation of early endosomes to Rab9/CD63-containing late endosomes. Nischarin is recruited to the SCV in a Rab14-dependent manner and enhances acidification of the SCV. Depletion of Nischarin or the Nischarin binding partners--Rac1, Rab14 and Rab9 GTPases--reduced the intracellular growth of Salmonella. Thus, interaction of Nischarin with GTPases may regulate maturation and subsequent acidification of vacuoles produced after phagocytosis of pathogens.

Improvement of hyperphagia by activation of cerebral I(1)-imidazoline receptors in streptozotocin-induced diabetic mice.

Imidazoline I1-receptors (I1R) are known to regulate blood pressure and rilmenidine, an agonist, is widely used as antihypertensive agent in clinic. However, the role of I1R in feeding behavior is still unclear. In the present study, we used the agonist of I1R to investigate the effect on hyperphagia in streptozotocin (STZ)-induced diabetic mice. Rilmenidine decreased the food intake of STZ-diabetic mice in a dose-dependent manner. The reduction of food intake was abolished by pretreatment with efaroxan at the dose sufficient to block I1R. Intracerebroventricular (icv) administration of rilmenidine into STZ-diabetic mice also significantly reduced hyperphagia, which was reversed by icv administration of efaroxan. In addition, similar results were observed in STZ-diabetic mice, which received chronic treatment with rilmenidine 3 times daily (t.i.d.) for 7 days. Moreover, the hypothalamic neuropeptide Y (NPY) level was reduced by rilmenidine that was also reversed by pretreatment with efaroxan. In conclusion, the obtained results suggest that rilmenidine can decrease food intake in STZ-diabetic mice through an activation of I1R to lower hypothalamic NPY level.