bims-stacyt 2018-06-17 papers

Kidney Int. 2018 Jun 07. pii: S0085-2538(18)30250-3. [Epub ahead of print]

Palmitate deranges erythropoietin production via transcription factor ATF4 activation of unfolded protein response.

Thitinun Anusornvongchai, Masaomi Nangaku, Tzu-Ming Jao, Chia-Hsien Wu, Yu Ishimoto, Hiroshi Maekawa, Tetsuhiro Tanaka, Akira Shimizu, Masayuki Yamamoto, Norio Suzuki, Ryoji Sassa, Reiko Inagi.

Lipotoxicity plays an important role in the progression of chronic kidney damage via various mechanisms, such as endoplasmic reticulum stress. Several studies proposed renal lipotoxicity in glomerular and tubular cells but the effect of lipid on renal erythropoietin (EPO)-producing (REP) cells in the interstitium has not been elucidated. Since renal anemia is caused by derangement of EPO production in REP cells, we evaluated the effect of palmitate, a representative long-chain saturated fatty acid, on EPO production and the endoplasmic reticulum stress pathway. EPO production was suppressed by palmitate (palmitate-conjugated bovine serum albumin [BSA]) or a high palmitate diet, but not oleic acid-conjugated BSA or a high oleic acid diet, especially under cobalt-induced pseudo-hypoxia both in vitro and in vivo. Importantly, suppression of EPO production was not induced by a decrease in transcription factor HIF activity, while it was significantly associated with endoplasmic reticulum stress, particularly transcription factor ATF4 activation, which suppresses 3'-enhancer activity of the EPO gene. ATF4 knockdown by siRNA significantly attenuated the suppressive effect of palmitate on EPO production. Studies utilizing inherited super-anemic mice (ISAM) mated with EPO-Cre mice (ISAM-REC mice) for lineage-labeling of REP cells showed that ATF4 activation by palmitate suppressed EPO production in REP cells. Laser capture microdissection confirmed ATF4 activation in the interstitial area of ISAM-REC mice treated with palmitate-conjugated BSA. Thus, endoplasmic reticulum stress induced by palmitate suppressed EPO expression by REP cells in a manner independent of HIF activation. The link between endoplasmic reticulum stress, dyslipidemia, and hypoxia may contribute to development and progression of anemia in CKD.

Keywords: anemia; endoplasmic reticulum; erythropoietin; fibrosis; hypoxia; lipids

DOI: https://doi.org/10.1016/j.kint.2018.03.011

Biochem Biophys Res Commun. 2018 Jun 11. pii: S0006-291X(18)31327-5. [Epub ahead of print]

Octanoic acid potentiates glucose-stimulated insulin secretion and expression of glucokinase through the olfactory receptor in pancreatic β-cells.

Jaechan Leem, Hae-Min Shim, Hochan Cho, Jae-Hyung Park.

Olfactory receptors (ORs) are G protein-coupled receptors that mediate olfactory chemosensation, leading to the perception of smell. ORs are expressed in many tissues, but their functions are largely unknown. Here, we show that the olfactory receptor Olfr15 is highly and selectively expressed in both mouse pancreatic β-cells and MIN6 cells. In addition, octanoic acid (OA), a medium-chain fatty acid, potentiates glucose-stimulated insulin secretion (GSIS). The OA-induced enhancement of GSIS was inhibited by Olfr15 knockdown. Treatment with a PLC inhibitor or an Ins(1,4,5)P3 receptor (IP3R) antagonist also blocked the OA-induced enhancement of GSIS. These results suggest that OA potentiates GSIS via Olfr15 though the PLC-IP3 pathway. Furthermore, long-term treatment with OA increased cellular glucose uptake in MIN6 cells by up-regulating the expression of glucokinase (GK). Moreover, this process was blocked by an IP3R antagonist and a Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) inhibitor. Similarly, OA stimulated GK promoter activity, while either Olfr15 or CaMKIV knockdown blocked the stimulatory effect of OA on GK promoter activity. These results suggest that long-term treatment of OA induces GK promoter activity via Olfr15 through the IP3-CaMKK/CaMKIV pathway. In islets from type 2 diabetic mice, the expression level of Olfr15 and the OA-induced enhancement of GSIS were strongly reduced. Collectively, our results highlight the crucial role of the olfactory receptor Olfr15 in potentiating GSIS in pancreatic β-cells, suggesting that Olfr15 may be an important therapeutic target in type 2 diabetes.

Keywords: Glucokinase; Insulin secretion; Octanoic acid; Olfactory receptor; Pancreatic β-cell; Type 2 diabetes

DOI: https://doi.org/10.1016/j.bbrc.2018.06.015

Cytokine. 2018 Jun 06. pii: S1043-4666(18)30237-0. [Epub ahead of print]

Interferon-γ interferes with host cell metabolism during intracellular Chlamydia trachomatis infection.

Kensuke Shima, Nadja Kaeding, Iretiolu Mayokun Ogunsulire, Inga Kaufhold, Matthias Klinger, Jan Rupp.

Interferon-γ (IFN-γ) is a central mediator of host immune responses including T-cell differentiation and activation of macrophages for the control of bacterial pathogens. Anti-bacterial mechanisms of IFN-γ against the obligate intracellular bacteria Chlamydiatrachomatis in epithelial cells have been intensively investigated in the past, focusing on cellular tryptophan depletion by an IFN-γ induced expression of the indoleamine 2, 3-deoxygenase (IDO). In this study, we could show that IFN-γ treatment caused a significant reduction of the host cell glycolysis that was accompanied by a reduction of glucose transporter-1 (GLUT1) and hypoxia inducible factor-1α (HIF-1α) expression. Furthermore, C. trachomatis induced enhancement of glycolytic and mitochondrial activation were significantly suppressed by IFN-γ treatment. We could further show that glucose starvation, as observed under IFN-γ treatment, was associated with an attenuated antimicrobial efficacy of doxycycline (DOX) against C. trachomatis. In conclusions, anti-chlamydial activity of IFN-γ goes beyond tryptophan depletion including interference with cellular energy metabolism resulting reduced progeny, but also impaired antimicrobial susceptibility of C. trachomatis.

Keywords: Antimicrobial efficacy; C. trachomatis; GLUT1; Glycolysis; HIF-1α; IFN-γ; Mitochondria

DOI: https://doi.org/10.1016/j.cyto.2018.05.039