T Helper 2 Cytokine Signaling in Bone Marrow-Derived Fibroblasts: A Target for Renal Fibrosis

Radiation-induced fibrosis: Mechanisms and therapeutic strategies from an immune microenvironment perspective

Radiation-induced fibrosis (RIF) is a severe chronic complication of radiotherapy (RT) manifested by excessive extracellular matrix (ECM) components deposition within the irradiated area. The lung, heart, skin, jaw, pelvic organs and so on may be affected by RIF, which hampers body functions and quality of life. There is accumulating evidence suggesting that the immune microenvironment may play a key regulatory role in RIF. This article discussed the synergetic or antagonistic effects of immune cells and mediators in regulating RIF's development. Several potential preventative and therapeutic strategies for RIF were proposed based on the immunological mechanisms to provide clinicians with improved cognition and clinical treatment guidance.

MHC class II in renal tubules plays an essential role in renal fibrosis

Immunomodulation is considered a potential therapeutic approach for chronic kidney disease (CKD). Although it has been previously reported that CD4⁺ T cells contribute to the development of renal fibrosis, the role of MHC class II (MHCII) in the development of renal fibrosis remains largely unknown. The present study reports that the expression of MHCII molecules in renal cortical tubules is upregulated in mouse renal fibrosis models generated by unilateral ureter obstruction (UUO) and folic acid (FA). Proximal tubule epithelial cells (PTECs) are functional antigen-presenting cells that promote the proliferation of CD4⁺ T cells in an MHCII-dependent manner. PTECs from mice with renal fibrosis had a stronger ability to induce T cell proliferation and cytokine production than control cells. Global or renal tubule-specific ablation of H2-Ab1 significantly alleviated renal fibrosis following UUO or FA treatment. Renal expression of profibrotic genes showed a consistent reduction in H2-Ab1 gene-deficient mouse lines. Moreover, there was a marked increase in renal tissue CD4⁺ T cells after UUO or FA treatment and a significant decrease following renal tubule-specific ablation of H2-Ab1. Furthermore, renal tubule-specific H2-Ab1 gene knockout mice exhibited higher proportions of regulatory T cells (Tregs) and lower proportions of Th2 cells in the UUO- or FA-treated kidneys. Finally, Immunohistochemistry (IHC) studies showed increased renal expression of MHCII and the profibrotic gene α smooth muscle actin (α-SMA) in CKD patients. Together, our human and mouse data demonstrate that renal tubular MHCII plays an important role in the pathogenesis of renal fibrosis.

Pharmacological Inhibition of STAT6 Ameliorates Myeloid Fibroblast Activation and Alternative Macrophage Polarization in Renal Fibrosis

A hallmark of chronic kidney disease is renal fibrosis, which can result in progressive loss of kidney function. Currently, there is no effective therapy for renal fibrosis. Therefore, there is an urgent need to identify potential drug targets for renal fibrosis. In this study, we examined the effect of a selective STAT6 inhibitor, AS1517499, on myeloid fibroblast activation, macrophage polarization, and development of renal fibrosis in two experimental murine models. To investigate the effect of STAT6 inhibition on myeloid fibroblast activation, macrophage polarization, and kidney fibrosis, wild-type mice were subjected to unilateral ureteral obstruction or folic acid administration and treated with AS1517499. Mice treated with vehicle were used as control. At the end of experiments, kidneys were harvested for analysis of myeloid fibroblast activation, macrophage polarization, and renal fibrosis and function. Unilateral ureteral obstruction or folic acid administration induced STAT6 activation in interstitial cells of the kidney, which was significantly abolished by AS1517499 treatment. Mice treated with AS1517499 accumulated fewer myeloid fibroblasts and myofibroblasts in the kidney with ureteral obstruction or folic acid nephropathy compared with vehicle-treated mice. Moreover, AS1517499 significantly suppressed M2 macrophage polarization in the injured kidney. Furthermore, AS1517499 markedly reduced the expression levels of extracellular matrix proteins, and development of kidney fibrosis and dysfunction. These findings suggest that AS1517499 inhibits STAT6 activation, suppresses myeloid fibroblast activation, reduces M2 macrophage polarization, attenuates extracellular matrix protein production, and preserves kidney function. Therefore, targeting STAT6 with AS1517499 is a novel therapeutic approach for chronic kidney disease.

Natural killer T cell/IL-4 signaling promotes bone marrow-derived fibroblast activation and M2 macrophage-to-myofibroblast transition in renal fibrosis

Renal fibrosis is a histological manifestation of chronic kidney disease. Natural killer T (NKT) cells have a critical role in the pathogenesis of fibrotic disorder. However, the role of NKT cells in regulating kidney fibrosis remains largely unknown. In the current study, we showed that the percentages of NKT⁺ cells and NKT⁺-IL-4⁺ cells were notably increased in folic acid (FA) and obstructive nephropathy. CD1d deficiency protected mice from renal fibrosis induced by FA and obstructive injury. Specifically, Loss of CD1d reduced bone marrow-derived myofibroblasts and CD206⁺/α-smooth muscle actin⁺ cells in the kidneys of injured mice. But mice treated with α-galactosylceramide (α-GC, a specific activator of NKT cells) developed more severe fibrosis, accumulated more myeloid myofibroblasts and M2 macrophages-myofibroblasts transition (M2MMT) cells in FA injured kidneys. Furthermore, IL-4 expression was markedly reduced in CD1d deficiency mice but increased in α-GC-treated mice. Administration of IL-4 abrogates the inhibiting effect of CD1d deficiency on renal fibrosis, bone marrow-derived fibroblasts activation, and M2MMT in FA injured kidneys. Conversely, pharmacological inhibition of IL-4 attenuated the development of renal fibrosis, decreased bone marrow-derived myofibroblasts, and suppressed M2MMT. Thus, this study revealed a novel role of NKT cells in the bone marrow-derived fibroblasts activation and M2MMT during renal fibrosis. Targeting NKT cell/IL-4 signaling may be an effective treatment for renal fibrosis.

The IL-4 receptor α has a critical role in bone marrow-derived fibroblast activation and renal fibrosis

Renal fibrosis is a common pathway leading to the progression of chronic kidney disease, and bone marrow-derived fibroblasts contribute significantly to the development of renal fibrosis. However, the signaling mechanisms underlying the activation of these fibroblasts are not completely understood. Here, we examined the role of IL-4 receptor α (IL-4Rα) in the activation of myeloid fibroblasts in two experimental models of renal fibrosis. Compared with wild-type mice, IL-4Rα knockout mice accumulated fewer bone marrow-derived fibroblasts and myofibroblasts in their kidneys. IL-4Rα deficiency suppressed the expression of α-smooth muscle actin, extracellular matrix proteins and the development of renal fibrosis. Furthermore, IL-4Rα deficiency inhibited the activation of signal transducer and activator of transcription 6 (STAT6) in the kidney. Moreover, wild-type mice engrafted with bone marrow cells from IL-4Rα knockout mice exhibited fewer myeloid fibroblasts in the kidney and displayed less severe renal fibrosis following ureteral obstructive injury compared with wild-type mice engrafted with wild-type bone marrow cells. In vitro, IL-4 activated STAT6 and stimulated expression of α-smooth muscle actin and fibronectin in mouse bone marrow monocytes. This was abolished in the absence of IL-4Rα. Thus, IL-4Rα plays an important role in bone marrow-derived fibroblast activation, resulting in extracellular matrix protein production and fibrosis development. Hence, the IL-4Rα/STAT6 signaling pathway may serve as a novel therapeutic target for chronic kidney disease.

Recent Advances in Magnetic Resonance Imaging Assessment of Renal Fibrosis

CKD is a global public health problem. Renal fibrosis is a final common pathway leading to progressive loss of function in CKD. The degree of renal fibrosis predicts the prognosis of CKD. Recent studies have shown that bone marrow-derived fibroblasts contribute significantly to the development of renal fibrosis, which may yield novel therapeutic strategy for fibrotic kidney disease. Therefore, it is imperative to accurately assess the degree of renal fibrosis noninvasively to identify those patients who can benefit from antifibrotic therapy. In this review, we summarize recent advances in the assessment of renal fibrosis by magnetic resonance imaging.

Peroxisome proliferator-activated receptor-γ agonist pioglitazone fails to attenuate renal fibrosis caused by unilateral ureteral obstruction in mice

Renal tubulointerstitial fibrosis is the common ending of progressive renal disease. It is worth developing new ways to stop the progress of renal fibrosis. Peroxisome proliferator-activated receptor-γ (PPARγ) agonists have been studied to treat diabetic nephropathy, cisplatin-induced acute renal injury, ischemia reperfusion injury and adriamycin nephropathy. In this study, unilateral ureteral obstruction (UUO) was used to establish a different renal fibrosis model. PPAR? agonist pioglitazone was administrated by oral gavage and saline was used as control. At 7th and 14th day after the operation, mice were sacrificed for fibrosis test and T lymphocytes subsets test. Unexpectedly, through MASSON staining, immunohistochemistry for α-SMA, and Western blotting for a-SMA and PDGFR-β, we found that pioglitazone failed to attenuate renal fibrosis in UUO mice. However, flow cytometry showed that pioglitazone down-regulated Th1 cells, and up-regulated Th2 cells, Th17 cells and Treg cells. But the Th17/Treg ratio had no significant change by pioglitazone. Real-time PCR results showed that TGF-β and MCP-1 had no significant changes, at the same time, CD4(+) T cells associated cytokines were partially regulated by pioglitazone pretreatment. Taken together, pioglitazone failed to suppress renal fibrosis progression caused by UUO.