MKP-1 Deficiency Exacerbates Skin Fibrosis in a Mouse Model of Scleroderma

Scleroderma is a chronic fibrotic disease, where proinflammatory and profibrotic events precede collagen accumulation. MKP-1 [mitogen-activated protein kinase (MAPK) phosphatase-1] downregulates inflammatory MAPK pathways suppressing inflammation. MKP-1 also supports Th1 polarization, which could shift Th1/Th2 balance away from profibrotic Th2 profile prevalent in scleroderma. In the present study, we investigated the potential protective role of MKP-1 in scleroderma. We utilized bleomycin-induced dermal fibrosis model as a well-characterized experimental model of scleroderma. Dermal fibrosis and collagen deposition as well as the expression of inflammatory and profibrotic mediators were analyzed in the skin samples. Bleomycin-induced dermal thickness and lipodystrophy were increased in MKP-1-deficient mice. MKP-1 deficiency enhanced collagen accumulation and increased expression of collagens, 1A1 and 3A1, in the dermis. Bleomycin-treated skin from MKP-1-deficient mice also showed enhanced expression of inflammatory and profibrotic factors IL-6, TGF-β1, fibronectin-1 and YKL-40, and chemokines MCP-1, MIP-1α and MIP-2, as compared to wild-type mice. The results show, for the first time, that MKP-1 protects from bleomycin-induced dermal fibrosis, suggesting that MKP-1 favorably modifies inflammation and fibrotic processes that drive the pathogenesis of scleroderma. Compounds enhancing the expression or activity of MKP-1 could thus prevent fibrotic processes in scleroderma and possess potential as a novel immunomodulative drug.

Dysregulation of Lipid Metabolism in Mkp-1 Deficient Mice during Gram-Negative Sepsis

Mitogen-activated protein kinase phosphatase (Mkp)-1 exerts its anti-inflammatory activities during Gram-negative sepsis by deactivating p38 and c-Jun N-terminal kinase (JNK). We have previously shown that Mkp-1^+/+ mice, but not Mkp-1^-/- mice, exhibit hypertriglyceridemia during severe sepsis. However, the regulation of hepatic lipid stores and the underlying mechanism of lipid dysregulation during sepsis remains an enigma. To understand the molecular mechanism underlying the sepsis-associated metabolic changes and the role of Mkp-1 in the process, we infected Mkp-1^+/+ and Mkp-1^-/- mice with Escherichia coli i.v., and assessed the effects of Mkp-1 deficiency on tissue lipid contents. We also examined the global gene expression profile in the livers via RNA-seq. We found that in the absence of E. coli infection, Mkp-1 deficiency decreased liver triglyceride levels. Upon E. coli infection, Mkp-1^+/+ mice, but not Mkp-1^-/- mice, developed hepatocyte ballooning and increased lipid deposition in the livers. E. coli infection caused profound changes in the gene expression profile of a large number of proteins that regulate lipid metabolism in wildtype mice, while these changes were substantially disrupted in Mkp-1^-/- mice. Interestingly, in Mkp-1^+/+ mice E. coli infection resulted in downregulation of genes that facilitate fatty acid synthesis but upregulation of Cd36 and Dgat2, whose protein products mediate fatty acid uptake and triglyceride synthesis, respectively. Taken together, our studies indicate that sepsis leads to a substantial change in triglyceride metabolic gene expression programs and Mkp-1 plays an important role in this process.

MKP-1 signaling events are required for early osteoclastogenesis in lineage defined progenitor populations by disrupting RANKL-induced NFATc1 nuclear translocation

Cytokine-directed osteoclastogenesis is initiated in response to macrophage colony stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) to drive formation of osteoclasts (OC), large bone resorptive cells of hematopoietic origin. RANKL-induced signaling activates the MAPK pathways, which initiates nuclear translocation of the master regulator of osteoclast formation, transcription factor NFATc1. Proper control over these signaling events is essential to normal OC formation response to stimuli. MAPK phosphatase 1 (MKP-1), a serine and tyrosine phosphatase encoded by the gene Dusp1, functions to dephosphorylate and subsequently inactivate MAPK (p38 and JNK) signaling essential in osteoclastogenesis. Here, we explored the role of MKP-1 during RANKL-driven osteoclastogenesis from defined (B220/CD45(-)GR1(-)CD11b(lo/-)CD115(+)) OC progenitor (dOCP) populations using WT and Dusp1(-/-) global knockout mice. Sorted cells were driven to OC by M-CSF pre-treatment followed by RANKL stimulation for 3days. OC formation and qPCR products were analyzed for maturation. Results indicate that Dusp1(-/-) dOCP form less numerous, significantly smaller and less functional OC compared to WT controls. These data were corroborated by mRNA expression of the key OC genes, Nfatc1 and Tm7sf4 (DC-STAMP), which were significantly reduced in early osteoclastogenesis in OC progenitor from Dusp1(-/-) mice. Intriguingly, our data reveals that MKP-1 may positively control OC formation in response to RANKL by regulating NFATc1 nuclear translocation. Collectively, this report supports the idea that MKP-1 signaling is essential in early osteoclastogenesis in response to RANKL-induced signaling.

Interleukin-17A stimulates cardiac fibroblast proliferation and migration via negative regulation of the dual-specificity phosphatase MKP-1/DUSP-1

The dual-specificity mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) inactivates MAP kinases by dephosphorylation. Here we show that the proinflammatory cytokine interleukin (IL)-17A induces adult mouse primary cardiac fibroblast (CF) proliferation and migration via IL-17 receptor A//IL-17 receptor C-dependent MKP-1 suppression, and activation of p38 MAPK and ERK1/2. IL-17A mediated p38 MAPK and ERK1/2 activation is inhibited by MKP-1 overexpression, but prolonged by MKP-1 knockdown. IL-17A induced miR-101 expression via PI3K/Akt, and miR-101 inhibitor reversed MKP-1 down regulation. Importantly, MKP-1 knockdown, pharmacological inhibition of p38 MAPK and ERK1/2, or overexpression of dominant negative MEK1, each markedly attenuated IL-17A-mediated CF proliferation and migration. Similarly, IL-17F and IL-17A/F heterodimer that also signal via IL-17RA/IL-17RC, stimulated CF proliferation and migration. These results indicate that IL-17A stimulates CF proliferation and migration via Akt/miR-101/MKP-1-dependent p38 MAPK and ERK1/2 activation. These studies support a potential role for IL-17 in cardiac fibrosis and adverse myocardial remodeling.

Mitogen-activated protein kinase phosphatase-1 deficiency decreases atherosclerosis in apolipoprotein E null mice by reducing monocyte chemoattractant protein-1 levels

RATIONALE

We previously reported that mitogen-activated protein kinase phosphatase-1 (MKP-1) expression is necessary for oxidized phospholipids to induce monocyte chemoattractant protein-1 (MCP-1) secretion by human aortic endothelial cells. We also reported that inhibition of tyrosine phosphatases including MKP-1 ameliorated atherosclerotic lesions in mouse models of atherosclerosis.

OBJECTIVE

This study was conducted to further investigate the specific role of MKP-1 in atherogenesis.

METHODS AND RESULTS

We generated MKP-1(-/-)/apoE(-/-) double-knockout mice. At 24weeks of age, the size, macrophage and dendritic cell content of atherosclerotic lesions of the aortic root were significantly lower ( approximately -41% for lesions and macrophages, and approximately -78% for dendritic cells) in MKP-1(-/-)/apoE(-/-) mice when compared with apoE(-/-) mice. Total cholesterol (-18.4%, p=0.045) and very low-density lipoprotein (VLDL)/low-density lipoprotein (LDL) cholesterol (-20.0%, p=0.052) levels were decreased in MKP-1(-/-)/apoE(-/-) mice. Serum from MKP-1(-/-)/apoE(-/-) mice contained significantly lower levels of MCP-1 and possessed significantly reduced capability to induce monocyte migration in vitro. Moreover, peritoneal macrophages isolated from MKP-1(-/-)/apoE(-/-) mice produced significantly lower levels of MCP-1 when compared to peritoneal macrophages from apoE(-/-) mice. Furthermore, MKP-1(-/-)/apoE(-/-) mice had significantly reduced serum hydroxyeicosatetraenoic acids (HETEs) levels, which have been reported to induce MCP-1 levels.

CONCLUSIONS

Our results demonstrate that MKP-1 deficiency significantly decreases atherosclerotic lesion development in mice, in part, by affecting MCP-1 levels in the circulation and MCP-1 production by macrophages. MKP-1 may serve as a potential therapeutic target for the treatment of atherosclerotic disease.

Deletion of mitogen-activated protein kinase phosphatase 1 modifies the response to mechanical bone marrow ablation in a mouse model

The maintenance of bone mass results from a delicate balance between bone formation by osteoblasts and bone resorption by osteoclasts. Understanding these processes is essential for the development of effective treatments for skeletal diseases. Mechanical bone marrow ablation provides a unique animal model to study bone repair and the roles of specific genes in this process. Ablation of marrow induces the formation of intramembranous bone in the medullary cavity, which is subsequently resorbed by osteoclasts. We used this model to ask whether mitogen-activated protein kinase (MAPK) phosphatase 1 (MKP1) affects the bone formed in response to marrow ablation. MKP1 is a negative regulator of MAPK signaling, which is essential for a wide variety of cellular mechanisms, including those critical for osteoblast and osteoclast function. At 10 d after mechanical bone marrow ablation, the femurs of male mkp1(+/+) and mkp1(-/-) mice were compared with those of unoperated baseline mice by using radiography, peripheral quantitative computed tomography, and microcomputed tomography. Both genotypes developed increased bone mass after marrow ablation, but the increase was more pronounced in mkp1(-/-) mice compared with mkp1(+/+) mice. These results indicate that MKP1 affects the bone formed in response to marrow ablation and suggest encouraging possibilities for the use of inhibitors of MKP1 to modulate bone repair.

ERK-dependent MKP-1-mediated cisplatin resistance in human ovarian cancer cells

Mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) is the MAPK phosphatase family member that negatively regulates MAPK signaling. Our previous study showed that MKP-1 is involved in cisplatin resistance, but the mechanism underlying its resistance is not understood. Here, we show that ERK2-mediated MKP-1 expression is critical for cisplatin resistance. Specifically, we showed that in the human ovarian cancer cell lines, cisplatin induces MKP-1 through phosphorylation. We also showed that inhibition of ERK2 activity by the MEK1/2 inhibitor U0126 or by small interfering RNA silencing decreases MKP-1 induction, leading to an increase in cisplatin-induced cell death, which mimicked the results obtained with cells in which MKP-1 is down-regulated. Importantly, down-regulation of ERK2 decreased cisplatin-induced MKP-1 phosphorylation, suggesting that MKP-1 phosphorylation depends on ERK2 activity. Furthermore, down-regulation of ERK2 or MKP-1 enhanced cisplatin-induced apoptosis. In addition, we showed that down-regulation of ERK2 or MKP-1 decreases the basal level of Bcl-2 protein and that inhibition of Bcl-2 activity sensitizes ovarian cancer cells to cisplatin. Collectively, our results indicate that induction of MKP-1 by cisplatin is through phosphorylation involving ERK signaling and that MKP-1 plays a critical role in ERK-mediated cisplatin resistance. Thus, our results suggest that targeting ERK-MKP-1 signaling could overcome cisplatin resistance in human ovarian cancer.