Obesity is associated with a state of chronic low-grade inflammation, which contributes to insulin resistance and type 2 diabetes. However, the molecular mechanisms that link obesity to inflammation are not fully understood. Follistatin-like 1 (FSTL1) is a novel proinflammatory cytokine that is expressed in adipose tissue and secreted by preadipocytes/adipocytes. We aimed to test whether FSTL1 could have a role in obesity-induced inflammation and insulin resistance. It was found that FSTL1 expression was markedly decreased during differentiation of 3T3-L1 preadipocytes but reinduced by TNF-α. Furthermore, a significant increase in FSTL1 levels was observed in adipose tissue of obese ob/ob mice, as well as in serum of overweight/obese subjects. Mechanistic studies revealed that FSTL1 induced inflammatory responses in both 3T3-L1 adipocytes and RAW264.7 macrophages. The expression of proinflammatory mediators including IL-6, TNF-α, and MCP-1 was upregulated by recombinant FSTL1 in a dose-dependent manner, paralleled with activation of the IKKβ-NFκB and JNK signaling pathways in the two cell lines. Moreover, FSTL1 impaired insulin signaling in 3T3-L1 adipocytes, as revealed by attenuated phosphorylation of both Akt and IRS-1 in response to insulin stimulation. Together, our results suggest that FSTL1 is a potential mediator of inflammation and insulin resistance in obesity.

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SUMMARYThe epididymis and efferent ducts play major roles in sperm maturation, transport, concentration and storage by reabsorbing water, ions and proteins produced from seminiferous tubules. Gpr48-null male mice demonstrate reproductive tract defects and infertility. In the present study, we found that estrogen receptor  (ER) was dramatically reduced in the epididymis and efferent ducts in Gpr48-null male mice. We further revealed that ER could be upregulated by Gpr48 activation via the cAMP/PKA signaling pathway. Moreover, we identified a cAMP responsive element (Cre) motif located at -1307 to -1300 bp in the ER promoter that is able to interact with Cre binding protein (Creb). In conclusion, Gpr48 participates in the development of the male epididymis and efferent ducts through regulation of ER expression via the cAMP/PKA signaling pathway. KEY WORDS: Gpr48, ER(Esr1), Creb, Epididymis, Infertility, MouseG protein-coupled receptor 48 upregulates estrogen receptor  expression via cAMP/PKA signaling in the male reproductive tract DEVELOPMENT 152 is observed in Gpr48-null mice. The expression of ER, NHE3 and aquaporin 1 (Aqp1) is reduced in the proximal segment of the efferent ducts.In the present study, we investigated the role of Gpr48 in the regulation of ER expression and further explored the molecular mechanism underlying this regulation. MATERIALS AND METHODS MiceGpr48-null male mice were housed at 21±1°C with a humidity of 55±10% and a 12-hour light-dark cycle. Food and water were available ad libitum. For genotyping analysis, genomic DNA was isolated from tail biopsy and PCR was carried out using three primers: upstream primer 5Ј-CCAGTCACCACTCTTACACAATGGCTAAAC-3Ј; and downstream primers 5Ј-GGTCTTTGAGCACCAGAGGAC-3Ј and 5Ј-TCCCGTAG -GAGATAGCGTCCTAG-3Ј. With regard to the male fertility assay, each Gpr48+/-and Gpr48 -/-adult male aged 12 weeks was housed with two Gpr48 +/+ females. The females were examined daily for vaginal plugs. The litter number was counted immediately after parturition. The animal protocol was reviewed and approved by the Animal Care Committee of Shanghai Jiao Tong University School of Medicine. Ligation operationTwenty-four mice at 3 weeks of age received bilateral efferent ductile ligation (EGL; n8), bilateral vasoligation (VGL; n8) and sham operations (n8). For EGL, the efferent ductule was doubly ligated close to the epididymis and away from the epididymal and testicular vasculature and vas deferens. For VGL, bilateral vasa deferentia were doubly ligated. The mice receiving EGL, VGL or sham operations were observed daily to ascertain a normal descending of the testes. Immunofluorescence and immunohistochemical stainingAnimal tissues were fixed overnight in Bouin's solution, dehydrated in ethanol, embedded in paraffin and sectioned at 5 m. Immunofluorescence and immunohistochemical staining were performed according to a standard protocol. In brief, the sections were de-paraffined, progressively rehydrated and treated with 3% hydrogen peroxide in methanol for 30 minutes...

Aldosterone and the mineralocorticoid receptor (MR) are critical to the maintenance of electrolyte and BP homeostasis. Mutations in the MR cause aldosterone resistance known as pseudohypoaldosteronism type 1 (PHA1); however, some cases consistent with PHA1 do not exhibit known gene mutations, suggesting the possibility of alternative genetic variants. We observed that G protein-coupled receptor 48 (Gpr48/ Lgr4) hypomorphic mutant (Gpr48 m/m ) mice had hyperkalemia and increased water loss and salt excretion despite elevated plasma aldosterone levels, suggesting aldosterone resistance. When we challenged the mice with a low-sodium diet, these features became more obvious; the mice also developed hyponatremia and increased renin expression and activity, resembling a mild state of PHA1. There was marked renal downregulation of MR and its downstream targets (e.g., the a-subunit of the amiloride-sensitive epithelial sodium channel), which could provide a mechanism for the aldosterone resistance. We identified a noncanonical cAMP-responsive element located in the MR promoter and demonstrated that GPR48 upregulates MR expression via the cAMP/protein kinase A pathway in vitro. Taken together, our data demonstrate that GPR48 enhances aldosterone responsiveness by activating MR expression, suggesting that GPR48 contributes to homeostasis of electrolytes and BP and may be a candidate gene for PHA1.