Instructive Role of the Microenvironment in Preventing Renal Fibrosis

Accumulation of myofibroblasts is a hallmark of renal fibrosis. A significant proportion of myofibroblasts has been reported to originate via endothelial-mesenchymal transition. We initially hypothesized that exposing myofibroblasts to the extract of endothelial progenitor cells (EPCs) could reverse this transition. Indeed, in vitro treatment of transforming growth factor-beta1 (TGF-beta1)-activated fibroblasts with EPC extract prevented expression of alpha-smooth muscle actin (alpha-SMA); however, it did not enhance expression of endothelial markers. In two distinct models of renal fibrosis-unilateral ureteral obstruction and chronic phase of folic acid-induced nephropathy-subcapsular injection of EPC extract to the kidney prevented and reversed accumulation of alpha-SMA-positive myofibroblasts and reduced fibrosis. Screening the composition of EPC extract for cytokines revealed that it is enriched in leukemia inhibitory factor (LIF) and vascular endothelial growth factor. Only LIF was capable of reducing fibroblast-to-myofibroblast transition of TGF-beta1-activated fibroblasts. In vivo subcapsular administration of LIF reduced the number of myofibroblasts and improved the density of peritubular capillaries; however, it did not reduce the degree of fibrosis. A receptor-independent ligand for the gp130/STAT3 pathway, hyper-interleukin-6 (hyper-IL-6), not only induced a robust downstream increase in pluripotency factors Nanog and c-Myc but also exhibited a powerful antifibrotic effect. In conclusion, EPC extract prevented and reversed fibroblast-to-myofibroblast transition and renal fibrosis. The component of EPC extract, LIF, was capable of preventing development of the contractile phenotype of activated fibroblasts but did not eliminate TGF-beta1-induced collagen synthesis in cultured fibroblasts and models of renal fibrosis, whereas a receptor-independent gp130/STAT3 agonist, hyper-IL-6, prevented fibrosis. In summary, these studies, through the evolution from EPC extract to LIF and then to hyper-IL-6, demonstrate the instructive role of microenvironmental cues and may provide in the future a facile strategy to prevent and reverse renal fibrosis. Stem Cells Translational Medicine 2017;6:992-1005

Tumor necrosis factor-alpha induced expression of matrix metalloproteinase-9 through p21-activated Kinase-1

Background Expressed in embryonic development, matrix metalloprotein-9 (MMP-9) is absent in most of developed adult tissues, but recurs in inflammation during tissue injury, wound healing, tumor formation and metastasis. Expression of MMP-9 is tightly controlled by extracellular cues including pro-inflammatory cytokines and extracellular matrix (ECM). While the pathologic functions of MMP-9 are evident, the intracellular signaling pathways to control its expression are not fully understood. In this study we investigated mechanism of cytokine induced MMP-9 with particular emphasis on the role of p21-activated-kinase-1 (PAK1) and the down stream signaling. Results In response to TNF-alpha or IL-1alpha, PAK1 was promptly activated, as characterized by a sequential phosphorylation, initiated at threonine-212 followed by at threonine-423 in the activation loop of the kinase, in human skin keratinocytes, dermal fibroblasts, and rat hepatic stellate cells. Ectopic expression of PAK1 variants, but not p38 MAP kinase, impaired the TNF-alpha-induced MMP-9 expression, while other MMPs such as MMP-2, -3 and -14 were not affected. Activation of Jun N-terminal kinase (JNK) and NF-kappaB has been demonstrated to be essential for MMP-9 expression. Expression of inactive PAK1 variants impaired JNK but not NF-kappaB activation, which consequently suppressed the 5'-promoter activities of the MMP-9 gene. After the cytokine-induced phosphorylation, both ectopically expressed and endogenous PAK1 proteins were promptly accumulated even in the condition of suppressing protein synthesis, suggesting the PAK1 protein is stabilized upon TNF-alpha stimulation. Stabilization of PAK1 protein by TNF-alpha treatment is independent of the kinase catalytic activity and p21 GTPase binding capacities. In contrast to epithelial cells, mesenchymal cells require 3-dimensional type-I collagen in response to TNF-alpha to massively express MMP-9. The collagen effect is mediated, in part, by boost JNK activation in a way to cooperate the cytokine signaling. Conclusion We identified a novel mechanism for MMP-9 expression in response to injury signals, which is mediated by PAK1 activation and stabilization leading JNK activation

Tumor necrosis factor-alpha induced expression of matrix metalloproteinase-9 through p21-activated Kinase-1

Abstract Background Expressed in embryonic development, matrix metalloprotein-9 (MMP-9) is absent in most of developed adult tissues, but recurs in inflammation during tissue injury, wound healing, tumor formation and metastasis. Expression of MMP-9 is tightly controlled by extracellular cues including pro-inflammatory cytokines and extracellular matrix (ECM). While the pathologic functions of MMP-9 are evident, the intracellular signaling pathways to control its expression are not fully understood. In this study we investigated mechanism of cytokine induced MMP-9 with particular emphasis on the role of p21-activated-kinase-1 (PAK1) and the down stream signaling. Results In response to TNF-alpha or IL-1alpha, PAK1 was promptly activated, as characterized by a sequential phosphorylation, initiated at threonine-212 followed by at threonine-423 in the activation loop of the kinase, in human skin keratinocytes, dermal fibroblasts, and rat hepatic stellate cells. Ectopic expression of PAK1 variants, but not p38 MAP kinase, impaired the TNF-alpha-induced MMP-9 expression, while other MMPs such as MMP-2, -3 and -14 were not affected. Activation of Jun N-terminal kinase (JNK) and NF-kappaB has been demonstrated to be essential for MMP-9 expression. Expression of inactive PAK1 variants impaired JNK but not NF-kappaB activation, which consequently suppressed the 5'-promoter activities of the MMP-9 gene. After the cytokine-induced phosphorylation, both ectopically expressed and endogenous PAK1 proteins were promptly accumulated even in the condition of suppressing protein synthesis, suggesting the PAK1 protein is stabilized upon TNF-alpha stimulation. Stabilization of PAK1 protein by TNF-alpha treatment is independent of the kinase catalytic activity and p21 GTPase binding capacities. In contrast to epithelial cells, mesenchymal cells require 3-dimensional type-I collagen in response to TNF-alpha to massively express MMP-9. The collagen effect is mediated, in part, by boost JNK activation in a way to cooperate the cytokine signaling. Conclusion We identified a novel mechanism for MMP-9 expression in response to injury signals, which is mediated by PAK1 activation and stabilization leading JNK activation.</p

Interleukin-1 as an injury signal mobilizes retinyl esters in hepatic stellate cells through down regulation of lecithin retinol acyltransferase.

Retinoids are mostly stored as retinyl esters in hepatic stellate cells (HSCs) through esterification of retinol and fatty acid, catalyzed by lecithin-retinol acyltransferase (LRAT). This study is designated to address how retinyl esters are mobilized in liver injury for tissue repair and wound healing. Initially, we speculated that acute inflammatory cytokines may act as injury signal to mobilize retinyl esters by down-regulation of LRAT in HSCs. By examining a panel of cytokines we found interleukin-1 (IL-1) can potently down-regulate mRNA and protein levels of LRAT, resulting in mobilization of retinyl esters in primary rat HSCs. To simulate the microenvironment in the space of Disse, HSCs were embedded in three-dimensional extracellular matrix, by which HSCs retaine quiescent phenotypes, indicated by up-regulation of LRAT and accumulation of lipid droplets. Upon IL-1 stimulation, LRAT expression went down together with mobilization of lipid droplets. Secreted factors from Kupffer cells were able to suppress LRAT expression in HSCs, which was neutralized by IL-1 receptor antagonist. To explore the underlying mechanism we noted that the stability of LRAT protein is not significantly regulated by IL-1, indicating the regulation is likely at transcriptional level. Indeed, we found that IL-1 failed to down-regulate recombinant LRAT protein expressed in HSCs by adenovirus, while transcription of endogenous LRAT was promptly decreased. Following liver damage, IL-1 was promptly elevated in a close pace with down-regulation of LRAT transcription, implying their causative relationship. After administration of IL-1, retinyl ester levels in the liver, as measured by LC/MS/MS, decreased in association with down-regulation of LRAT. Likewise, IL-1 receptor knockout mice were protected from injury-induced down-regulation of LRAT. In summary, we identified IL-1 as an injury signal to mobilize retinyl ester in HSCs through down-regulation of LRAT, implying a mechanism governing transition from hepatic injury to wound healing

Interleukin-1 induced mobilization of retinyl ester in primary rat hepatic stellate cells is related to down-regulation of LRAT.

<p>Primary rat HSCs were cultured on plastic plate and treated with or without IL-1α (10 ng/ml) for 3 days. (A) Phase contrast images of HSCs. (B) Vitamin A auto-fluorescence in HSCs under UV excitation. Arrows indicate the small droplets that undergo mobilization along cytoplasmic processes as visualized by UV excitation. (C) Retinyl palmitate storage was measured by LC/MS/MS analysis, by which all-trans retinoic acid was used as an internal control for sample normalization. Results are expressed as ng/10⁶ cells. *<i>P</i><0.05 (n = 6). (D) Immunofluorescence staining for LRAT (red) in HSCs. Nuclei are indicated by DAPI staining (blue). Original magnification ×200. (E) Densitometry (pixel) analysis of 5 independent images or fields. *<i>P</i><0.05.</p

Interleukin-1 suppresses LRAT expression in primary rat hepatic stellate cells cultured in 3D ECM.

<p>(A) HSCs in equal number were seeded on plastic or embedded in 3D ECM (type I collagen or Matrigel, 1×10⁵ cells in 0.4 cm³). After recovery, the cultures were treated with or without IL-1 (10 ng/ml) for 18 hours. LRAT gene expression was measured by Affymetrix DNA microarray analysis, which has been extensively calibrated for many genes by qRT-PCR. (B–D) The levels of LRAT protein expressed by HSCs cultured on plastic or in 3D ECM. The effects of IL-1 treatments on LRAT expression were measured by Western blot analysis. GAPDH was used as loading control. (E) Vitamin A autofluorescence in the cultures was visualized by UV excitation for HSCs cultured in 3D ECM treated with or without IL-1 for 3 days. Original magnification ×200.</p