Arid5a/IL-6/PAI-1 Signaling Is Involved in the Pathogenesis of Lipopolysaccharide-Induced Kidney Injury.

A systemic inflammatory response leads to widespread organ dysfunction, such as kidney dysfunction. Plasminogen activator inhibitor-1 (PAI-1) is involved in the pathogenesis of inflammatory kidney injury; however, the regulatory mechanism of PAI-1 in injured kidneys remains unclear. PAI-1 is induced by interleukin (IL)-6 in patients with sepsis. In addition, the stabilization of IL-6 is regulated by the adenine-thymine-rich interactive domain-containing protein 5a (Arid5a). Therefore, the aim of the present study was to examine the involvement of Arid5a/IL-6/PAI-1 signaling in lipopolysaccharide (LPS)-induced inflammatory kidney injury. LPS treatment to C57BL/6J mice upregulated Pai-1 mRNA in the kidneys. Enzyme-linked immunosorbent assay (ELISA) revealed that PAI-1 expression was induced in the culture supernatants of LPS-treated human umbilical vein endothelial cells, but not in those of LPS-treated human kidney 2 (HK-2) cells, a tubular cell line. Combined with single-cell analysis, endothelial cells were found to be responsible for PAI-1 elevation in LPS-treated kidneys. Administration of TM5441, a PAI-1 inhibitor, reduced the urinary albumin/creatinine ratio, concomitant with downregulation of Il-6 and Arid5a mRNA expressions. IL-6 treatment in LPS model mice further upregulated Pai-1 mRNA expression compared with LPS alone, accompanied by renal impairment. Furthermore, the expression of Il-6 and Pai-1 mRNA was lower in Arid5a knockout mice than in wild-type mice after LPS treatment. Taken together, the vicious cycle of Arid5a/IL-6/PAI-1 signaling is involved in LPS-induced kidney injury.

Transcription factor old astrocyte specifically induced substance is a novel regulator of kidney fibrosis.

Prevention of kidney fibrosis is an essential requisite for effective therapy in preventing chronic kidney disease (CKD). Here, we identify Old astrocyte specifically induced substance (OASIS)/cAMP responsive element-binding protein 3-like 1 (CREB3l1), a CREB/ATF family transcription factor, as a candidate profibrotic gene that drives the final common pathological step along the fibrotic pathway in CKD. Although microarray data from diseased patient kidneys and fibrotic mouse model kidneys both exhibit OASIS/Creb3l1 upregulation, the pathophysiological roles of OASIS in CKD remains unknown. Immunohistochemistry revealed that OASIS protein was overexpressed in human fibrotic kidney compared with normal kidney. Moreover, OASIS was upregulated in murine fibrotic kidneys, following unilateral ureteral obstruction (UUO), resulting in an increase in the number of OASIS-expressing pathological myofibroblasts. In vitro assays revealed exogenous TGF-ß1 increased OASIS expression coincident with fibroblast-to-myofibroblast transition and OASIS contributed to TGF-ß1-mediated myofibroblast migration and increased proliferation. Significantly, in vivo kidney fibrosis induced via UUO or ischemia/reperfusion injury was ameliorated by systemic genetic knockout of OASIS, accompanied by reduced myofibroblast proliferation. Microarrays revealed that the transmembrane glycoprotein Bone marrow stromal antigen 2 (Bst2) expression was reduced in OASIS knockout myofibroblasts. Interestingly, a systemic anti-Bst2 blocking antibody approach attenuated kidney fibrosis in normal mice but not in OASIS knockout mice after UUO, signifying Bst2 functions downstream of OASIS. Finally, myofibroblast-restricted OASIS conditional knockouts resulted in resistance to kidney fibrosis. Taken together, OASIS in myofibroblasts promotes kidney fibrosis, at least in part, via increased Bst2 expression. Thus, we have identified and demonstrated that OASIS signaling is a novel regulator of kidney fibrosis.

Maresin-1 induces cardiomyocyte hypertrophy through IGF-1 paracrine pathway.

The resolution of inflammation is closely linked with tissue repair. Recent studies have revealed that macrophages suppress inflammatory reactions by producing lipid mediators, called specialized proresolving mediators (SPMs); however, the biological significance of SPMs in tissue repair remains to be fully elucidated in the heart. In this study, we focused on maresin-1 (MaR1) and examined the reparative effects of MaR1 in cardiomyocytes. The treatment with MaR1 increased cell size in cultured neonatal rat cardiomyocytes. Since the expression of fetal cardiac genes was unchanged by MaR1, physiological hypertrophy was induced by MaR1. SR3335, an inhibitor of retinoic acid-related orphan receptor α (RORα), mitigated MaR1-induced cardiomyocyte hypertrophy, consistent with the recent report that RORα is one of MaR1 receptors. Importantly, in response to MaR1, cardiomyocytes produced IGF-1 via RORα. Moreover, MaR1 activated phosphoinositide 3-kinase (PI3K)/Akt signaling pathway and wortmannin, a PI3K inhibitor, or triciribine, an Akt inhibitor, abrogated MaR1-induced cardiomyocyte hypertrophy. Finally, the blockade of IGF-1 receptor by NVP-AEW541 inhibited MaR-1-induced cardiomyocyte hypertrophy as well as the activation of PI3K/Akt pathway. These data indicate that MaR1 induces cardiomyocyte hypertrophy through RORα/IGF-1/PI3K/Akt pathway. Considering that MaR1 is a potent resolving factor, MaR1 could be a key mediator that orchestrates the resolution of inflammation with myocardial repair.

CXCL10 is a novel anti-angiogenic factor downstream of p53 in cardiomyocytes.

Tumor suppressor protein p53 plays crucial roles in the onset of heart failure. p53 activation results in cardiac dysfunction, at least partially by suppressing angiogenesis. Though p53 has been reported to reduce VEGF production by inhibiting hypoxia-inducible factor, the anti-angiogenic property of p53 remains to be fully elucidated in cardiomyocytes. To explore the molecular signals downstream of p53 that regulate vascular function, especially under normoxic conditions, DNA microarray was performed using p53-overexpressing rat neonatal cardiomyocytes. Among genes induced by more than 2-fold, we focused on CXCL10, an anti-angiogenic chemokine. Real-time PCR revealed that p53 upregulated the CXCL10 expression as well as p21, a well-known downstream target of p53. Since p53 is known to be activated by doxorubicin (Doxo), we examined the effects of Doxo on the expression of CXCL10 and found that Doxo enhanced the CXCL10 expression, accompanied by p53 induction. Importantly, Doxo-induced CXCL10 was abrogated by siRNA knockdown of p53, indicating that p53 activation is necessary for Doxo-induced CXCL10. Next, we examined the effect of hypoxic condition on p53-mediated induction of CXCL10. Interestingly, CXCL10 was induced by hypoxia and its induction was potentiated by the overexpression of p53. Finally, the conditioned media from cultured cardiomyocytes expressing p53 decreased the tube formation of endothelial cells compared with control, analyzed by angiogenesis assay. However, the inhibition of CXCR3, the receptor of CXCL10, restored the tube formation. These data indicate that CXCL10 is a novel anti-angiogenic factor downstream of p53 in cardiomyocytes and could contribute to the suppression of vascular function by p53.

Myeloid cell-specific ablation of Runx2 gene exacerbates post-infarct cardiac remodeling.

Runt-related transcription factor 2 (Runx2), a regulator of osteoblast differentiation, is pathologically involved in vascular calcification; however, the significance of Runx2 in cardiac homeostasis remains unclear. Here, we investigated the roles of Runx2 in cardiac remodeling after myocardial infarction (MI). The expression of Runx2 mRNA and protein was upregulated in murine hearts after MI. Runx2 was expressed in heart-infiltrating myeloid cells, especially in macrophages, at the border zone of post-infarct myocardium. To analyze the biological functions of Runx2 in cardiac remodeling, myeloid cell-specific Runx2 deficient (CKO) mice were exposed to MI. After MI, ventricular weight/tibia length ratio was increased in CKO mice, concomitant with severe cardiac dysfunction. Cardiac fibrosis was exacerbated in CKO mice, consistent with the upregulation of collagen 1a1 expression. Mechanistically, immunohistochemical analysis using anti-CD31 antibody showed that capillary density was decreased in CKO mice. Additionally, conditioned culture media of myeloid cells from Runx2 deficient mice exposed to MI induced the tube formation of vascular endothelial cells to a lesser extent than those from control mice. RNA-sequence showed that the expression of pro-angiogenic or anti-angiogenic factors was altered in macrophages from Runx2-deficient mice. Collectively, Runx2+ myeloid cells infiltrate into post-infarct myocardium and prevent adverse cardiac remodeling, at least partially, by regulating endothelial cell function.