The role of mitogen-activated protein kinase and protein kinase C in fibronectin production in human vascular smooth muscle cells

Animal models of catheter-induced intimal hyperplasia in type 1 and type 2 diabetes and the effects of pharmacologic intervention

Diabetes is a complex disorder characterized by impaired insulin formation, release or action (insulin resistance), elevated blood glucose, and multiple long-term complications. It is a common endocrine disorder of humans and is associated with abnormalities of carbohydrate and lipid metabolism. There are two forms of diabetes, classified as type 1 and type 2. In type 1 diabetes, hyperglycemia is due to an absolute lack of insulin, whereas in type 2 diabetes, hyperglycemia is due to a relative lack of insulin and insulin resistance. More than 90% of people with diabetes have type 2 with varied degrees of insulin resistance. Insulin resistance is often associated with impaired insulin secretion, and hyperglycemia is a common feature in both types of diabetes, but failure to make a distinction between the types of diabetes in different animal models has led to confusion in the literature. This is particularly true in relation to cardiovascular disease in the presence of diabetes and especially the response to vascular injury, in which there are major differences between the two types of diabetes. Animal models do not completely mimic the clinical disease seen in humans. Animal models are at best analogies of the pathologic process they are designed to represent. The focus of this review is an analysis of intimal hyperplasia following catheter-induced vascular injury, including factors that may complicate comparisons between different animal models or between in vitro and in vivo studies. We examine the variables, pitfalls, and caveats that follow from the manner of induction of the injury and the diabetic state of the animal. The efficacy of selected antidiabetic drugs in inhibiting the development of the hyperplastic response is also discussed.

PKCδ Is Necessary for Smad3 Expression and Transforming Growth Factor β–Induced Fibronectin Synthesis in Vascular Smooth Muscle Cells

Objective— The purpose of these studies is to investigate the mechanism by which transforming growth factor (TGF)β1 regulates the synthesis of the extracellular matrix protein fibronectin (FN).

Methods and Results— TGFβ1 elicited a time-dependent induction of FN protein and mRNA in A10 rat aortic smooth muscle cells (SMCs). Ectopic expression of Smad3 in A10 cells stimulated both basal and TGFβ1-induced FN expression, whereas expression of Smad7 eliminated the TGFβ response. Because TGFβ activated PKCδ in SMCs, we tested the role of PKCδ in regulation of FN expression. Inhibition of PKCδ activity by rottlerin or dominant-negative adenovirus (AdPKCδ DN) blocked TGFβ1’s induction of FN, whereas overexpression of PKCδ enhanced TGFβ’s effect. Moreover, aortic SMCs isolated from PKCδ −/− mice exhibited diminished FN induction in response to TGFβ. Furthermore, we found that Smad3 protein and mRNA were markedly reduced in AdPKCδ DN-treated A10 cells and in PKCδ null cells. Finally, restoring Smad3 in rottlerin-treated A10 and PKCδ null cells rescues the ability of TGFβ to upregulate FN protein and mRNA expression.

Conclusion— Our data suggest that TGFβ-activated PKCδ is critical to maintain normal expression of Smad3, which in turn is required for the induction of fibronectin. PKCδ represents a promising target for treating the fibroproliferative response after arterial injury.

Role of protein kinase C and oxidative stress in interleukin-1beta-induced human proximal tubule cell injury and fibrogenesis

BACKGROUND

Interleukin (IL)-1beta, a pro-inflammatory macrophage-derived cytokine, is implicated as a key mediator of interstitial fibrosis and tubular loss or injury in progressive renal insufficiency. This study investigates some of the mechanisms of action of IL-1beta on the proximal tubule.

METHODS

Confluent cultures of primary human proximal tubule cells (PTC) were incubated in serum-free media supplemented with either IL-1beta (0-4 ng/mL), phorbol-12-myristate 13-acetate (PMA, protein kinase C activator) (6.25-100 nmol/L), or vehicle (control), together with a non-specific protein kinase C inhibitor (H7), a specific protein kinase C inhibitor (BIM-1), an anti-oxidant (NAC) or a NADPH oxidase inhibitor (AEBSF).

RESULTS

Interleukin-1beta-treated PTC exhibited time-dependent increases in fibronectin secretion (ELISA), cell injury (LDH release) and reactive nitrogen species (RNS) release (Griess assay). Proximal tubule cell DNA synthesis (thymidine incorporation) was also significantly suppressed. The effects of IL-1beta, which were reproduced by incubation of PTC with PMA (6.25-100 nmol/L), were blocked by H7 but not by BIM-1. The anti-oxidant (4 mmol/L) partially blocked IL-1beta-induced fibronectin secretion by PTC, but did not affect IL-1beta-induced LDH release, RNS release or growth inhibition. The NADPH oxidase inhibitor (AEBSF) significantly attenuated all observed deleterious effects of IL-1beta on PTC.

CONCLUSION

Interleukin-1beta directly induces proximal tubule injury, extracellular matrix production and impaired growth. The anti-oxidant, NAC, appears to ameliorate part of the fibrogenic effect of IL-1beta on PTC through mechanisms that do not significantly involve protein kinase C activation or nitric oxide release.

Vascular smooth muscle cell migration: current research and clinical implications

Atherosclerosis and intimal hyperplasia are major causes of morbidity and mortality. These processes develop secondary to endothelial injury due to multiple stimuli, including smoking, diabetes mellitus, hypertension, and hyperlipidemia. Once this injury occurs, an essential element in the development of both these processes is vascular smooth muscle cell (VSMC) migration. Understanding the mechanisms involved in VSMC migration and ultimately the development of strategies by which this process can be inhibited, has been a major focus of research. The authors present a review of the extracellular proteins (growth factors, extracellular matrix components, and cell surface receptors) and intracellular signaling pathways involved in VSMC migration, as well as potential therapeutic approaches to inhibit this process.

The ins and outs of fibronectin matrix assembly

Cell phenotype is specified by environmental cues embedded in the architecture and composition of the extracellular matrix (ECM). Much has been learned about matrix organization and assembly through analyses of the ECM protein fibronectin (FN). FN matrix assembly is a cell-mediated process in which soluble dimeric FN is converted into a fibrillar network. Binding of cell surface integrin receptors to FN converts it to an active form, which promotes fibril formation through interactions with other cell-associated FN dimers. As FN fibrils form on the outside of the cell, cytoplasmic domains of integrin receptors organize cytoplasmic proteins into functional complexes inside. Intracellular connections to the actin cytoskeletal network and stimulation of certain key intracellular signaling pathways are essential for FN-integrin interactions and propagation of FN fibril formation. Thus, assembly of native functional ECM depends on exquisite coordination between extracellular events and intracellular pathways.

Neuritogenesis induced by thyroid hormone-treated astrocytes is mediated by epidermal growth factor/mitogen-activated protein kinase-phosphatidylinositol 3-kinase pathways and involves modulation of extracellular matrix proteins

Thyroid hormone (T3) plays a crucial role in several steps of cerebellar ontogenesis. By using a neuron-astrocyte coculture model, we have investigated the effects of T3-treated astrocytes on cerebellar neuronal differentiation in vitro. Neurons plated onto T3-astrocytes presented a 40-60% increase on the total neurite length and an increment in the number of neurites. Treatment of astrocytes with epidermal growth factor (EGF) yielded similar results, suggesting that this growth factor might mediate T3-induced neuritogenesis. EGF and T3 treatment increased fibronectin and laminin expression by astrocytes, suggesting that astrocyte neurite permissiveness induced by these treatments is mostly due to modulation of extracellular matrix (ECM) components. Such increase in ECM protein expression as well as astrocyte permissiveness to neurite outgrowth was reversed by the specific EGF receptor tyrosine kinase inhibitor, tyrphostin. Moreover, studies using selective inhibitors of several transduction-signaling cascades indicated that modulation of ECM proteins by EGF is mainly through a synergistic activation of mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways. In this work, we provide evidence of a novel role of EGF as an intermediary factor of T3 action on cerebellar ontogenesis. By modulating the content of ECM proteins, EGF increases neurite outgrowth. Our data reveal an important role of astrocytes as mediators of T3-induced cerebellar development and partially elucidate the role of EGF and mitogen-activated protein kinase/phosphatidylinositol 3-kinase pathways on this process.

Regulation of fibronectin fibrillogenesis by protein kinases in cultured rat osteoblasts

Fibronectin (Fn) plays an important role in the regulation of adhesion, migration, and maturation of osteoblasts. Fn fibrillogenesis is involved in the process of bone mineralization. To elucidate the regulatory role of protein kinases in the formation of fibrillar Fn matrix, Fn synthesis and assembly were examined in cultured osteoblasts. Osteoblasts assembled the endogenously released soluble Fn into immobilized form on the substratum in a time-dependent manner. Both 12-O-tetradecanoylphorbol-13 acetate (TPA) and forskolin increased the synthesis of Fn. However, the extracellular assembly of Fn fibril from both endogenously released and exogenously applied soluble Fn was increased by TPA but decreased by forskolin. Protein kinase C (PKC) inhibitors, such as H7, Ro 318220, and Gö 6976, inhibited Fn fibrillogenesis. These results suggest that the dynamic of Fn fibrillogenesis is differentially regulated by the activation of PKC and protein kinase A (PKA). Both classic and novel isoforms of PKC are involved in the action of TPA in osteoblasts. It has been reported that alpha5beta1 integrin is related to Fn fibrillogenesis. Immunocytochemistry and flow cytometry showed that TPA and forskolin increased and inhibited, respectively, the clustering and surface expression of alpha5 integrins. TPA and forskolin did not affect protein levels of alpha5 integrins. The Western blot and reverse transcriptase-polymerase chain reaction showed that protein and mRNA levels of beta1 integrins also were not affected by TPA and forskolin. These results suggest that TPA and forskolin may affect the surface expression of alpha5beta1 integrins. cAMP response element-binding protein phosphorylation is involved in the action of forskolin but not that of TPA. Our results suggest that PKC activation enhanced Fn fibrillogenesis, whereas PKA activation inhibited extracellular Fn fibrillogenesis in primary cultured osteoblasts. Cytosolic Fn synthesis and extracellular Fn assembly may be differentially regulated by the activation of PKA.

Involvement of p38 MAP kinase in TGF-beta-stimulated VEGF synthesis in aortic smooth muscle cells

Although it is known that transforming growth factor (TGF)-beta induces vascular endothelial growth factor (VEGF) synthesis in vascular smooth muscle cells, the underlying mechanisms are still poorly understood. In the present study, we examined whether the mitogen-activated protein (MAP) kinase superfamily is involved in TGF-beta-stimulated VEGF synthesis in aortic smooth muscle A10 cells. TGF-beta stimulated the phosphorylation of p42/p44 MAP kinase and p38 MAP kinase, but not that of SAPK (stress-activated protein kinase)/JNK (c-Jun N-terminal kinase). The VEGF synthesis induced by TGF-beta was not affected by PD98059 or U0126, specific inhibitors of the upstream kinase that activates p42/p44 MAP kinase. We confirmed that PD98059 or U0126 did actually suppress the phosphorylation of p42/p44 MAP kinase by TGF-beta in our preparations. PD169316 and SB203580, specific inhibitors of p38 MAP kinase, significantly reduced the TGF-beta-stimulated synthesis of VEGF (each in a dose-dependent manner). PD169316 or SB203580 attenuated the TGF-beta-induced phosphorylation of p38 MAP kinase. These results strongly suggest that p38 MAP kinase plays a part in the pathway by which TGF-beta stimulates the synthesis of VEGF in aortic smooth muscle cells.

Localization of extracellular matrix and mitogen-activated protein kinase (MAPK) in aorta of streptozotocin treated Mongolian gerbils

To evaluate the relationship among the extracellular matrix (ECM) and mitogen-activated protein kinase (MAPK) family for the vascular damages in hyperglycemia, we injected Mongolian gerbils intravenously with 150 mg/kg streptozotocin (STZ) and observed over the next one year the resulting aortic changes by immunohistochemical techniques. After STZ treatment, hyperglycemia was confirmed. At 4 weeks after STZ administration morphological observation revealed increased stromal components among the vascular smooth muscle cells (SMCs). Immunohistochemically, extracellular matrices such as fibronectin and laminin were localized in the aorta at 4 weeks and one year after STZ administration. The reaction products of MAPK in vascular SMCs were more increased at one year than at 4 weeks after STZ administration. After STZ administration, the increase of ECM and MAPK was observed in the aorta, which suggests these factors play important roles in the pathogenesis of macrovasculopathy in diabetes mellitus.

p38 Map kinase regulates vascular smooth muscle cell collagen synthesis by angiotensin II in SHR but not in WKY

Vascular remodeling in hypertension is associated with cell growth and increased deposition of extracellular matrix components, particularly collagen. Mechanisms underlying these processes are unclear, but MAP kinases, particularly ERK1/2 and p38 MAP kinase, may be important. We studied the role of ERK1/2 and p38 MAP kinase in vascular smooth muscle cell (VSMC) collagen synthesis and growth mediated by angiotensin (Ang) II in spontaneously hypertensive rats (SHR). Cultured mesenteric VSMC from Wistar-Kyoto rats and SHR were used. Phosphorylation of ERK1/2 and p38 MAP kinase were assessed by Western blots with phosphospecific antibodies. Ang II-stimulated DNA and collagen synthesis were determined by measuring incorporation of (3)H-thymidine and (3)H-proline, respectively. mRNA expression of procollagen I and III was determined by reverse transcription-polymerase chain reaction. Ang II increased ERK1/2 and p38 MAP kinase phosphorylation. Responses were augmented in SHR. Effects were inhibited by irbesartan, a selective AT(1) antagonist, but not by PD123319, a selective AT(2) blocker. Ang II stimulated (3)H-thymidine and (3)H-proline incorporation. These actions were enhanced 2- to 3-fold in SHR. PD98059, selective inhibitor of the ERK1/2 pathway, attenuated Ang II-induced growth and collagen effects and normalized responses in SHR. SB212190, a selective p38 MAP kinase inhibitor, did not alter Ang II-elicited DNA synthesis but reduced collagen production and mRNA expression of procollagen I and III in SHR. These data demonstrate that (1) Ang II-mediated activation of p38 and ERK1/2 is increased in SHR, (2) augmented growth responses are generated by ERK1/2-dependent, p38 MAP kinase-independent pathways, and (3) p38 MAP kinase influences Ang II-induced collagen production in SHR but not in Wistar-Kyoto rats. These results indicate differential roles of ERK1/2 and p38 MAP kinase in AT(1)-stimulated VSMC growth and collagen production, which may contribute to vascular remodeling in hypertension.

Mechanisms by which bradykinin promotes fibrosis in vascular smooth muscle cells: role of TGF-beta and MAPK

Accumulation of extracellular matrix (ECM) is a hallmark feature of vascular disease. We have previously shown that hyperglycemia induces the expression of B(2)-kinin receptors in vascular smooth muscle cells (VSMC) and that bradykinin (BK) and hyperglycemia synergize to stimulate ECM production. The present study examined the cellular mechanisms through which BK contributes to VSMC fibrosis. VSMC treated with BK (10(-8) M) for 24 h significantly increased alpha(2)(I) collagen mRNA levels. In addition, BK produced a two- to threefold increase in alpha(2)(I) collagen promoter activity in VSMC transfected with a plasmid containing the alpha(2)(I) collagen promoter. Furthermore, treatment of VSMC with BK for 24 h produced a two- to threefold increase in the secretion rate of tissue inhibitor of metalloproteinase 1 (TIMP-1). The increase in alpha(2)(I) collagen mRNA levels and alpha(2)(I) collagen promoter activity, as well as TIMP-1 secretion, in response to BK were blocked by anti-transforming growth factor-beta (anti-TGF-beta) neutralizing antibodies. BK (10(-8) M) increased the endogenous production of TGF-beta1 mRNA and protein levels. Inhibition of the mitogen-activated protein kinase (MAPK) pathway by PD-98059 inhibited the increase of alpha(2)(I) collagen promoter activity, TIMP-1 production, and TGF-beta1 protein levels observed in response to BK. These findings provide the first evidence that BK induces collagen type I and TIMP-1 production via autocrine activation of TGF-beta1 and implicate MAPK pathway as a key player in VSMC fibrosis in response of BK.

Angiotensin II activates collagen I gene through a mechanism involving the MAP/ER kinase pathway

Vascular remodeling and rearrangement of the extracellular matrix formation are among the major adaptive mechanisms to chronic increase in blood pressure. In previous studies we have found that angiotensin II (Ang II) participates in the hypertension-associated aortic and renal vascular fibrosis by stimulating collagen type I formation. The purpose of the present study was to gain insight into the molecular events that lead from the Ang II receptor to collagen I gene activation. To this end, we used a novel strain of transgenic mice harboring the luciferase gene under the control of the collagen I-alpha(2) chain promoter [procolalpha(2)(I)]. Ang II produced an early (1 hour) 2- to 3-fold stimulation of procolalpha(2)(I) activity in freshly isolated aortas and renal cortical slices (P:<0. 01) followed by similar increase in procolalpha(2)(I) mRNA aortic levels. This effect of Ang II was inhibited by AT1-receptor antagonism (candesartan) and blockade of the MAPK/ERK cascade (PD98059); in contrast, inhibition of the P38 kinase pathway (SB202190) and blockade of the release of the transcription factor NFkappaB (PDTC) did not have any effect in the Ang II-induced activation of the collagen I gene. In addition, Ang II induced a rapid (5 minutes) increase of the MAPK/ERK activity that was accompanied by increased expression (3-fold) of the c-fos proto-oncogene. This increase of c-fos mRNA expression was blocked by PD98059; in addition, curcumin, a blocker of the transcriptional factor AP-1, canceled the effect of Ang II on the collagen I gene. Decorin, a scavenger of the active form of transforming growth factor-beta (TGF-beta), canceled the Ang II effect on collagen I gene, whereas inhibition of the MAPK/ERK pathway had no effect on the TGF-beta-induced activation of procolalpha(2)(I). These data indicate that the cellular events after AT1 receptor stimulation and leading to activation of collagen I gene expression require activation of both the MAPK/ERK and TGF-beta signaling pathways.

The effect of protein kinase C and its alpha subtype on human vascular smooth muscle cell proliferation, migration and fibronectin production

BACKGROUND

Vascular smooth muscle cell (SMC) migration, proliferation and extracellular matrix protein production are key steps in the formation of intimal hyperplasia, a process that leads to failure of vascular reconstructions. Protein kinase C (PKC) may be involved in all 3 cellular events. PKC consists of a family of 11 isotypes, 8 of which we have identified in human vascular SMCs. In this study we evaluate the role of PKCalpha as a second messenger for proliferation, migration and fibronectin production induced by human saphenous vein SMCs.

METHODS

DNA synthesis was evaluated by using (3)H-thymidine incorporation. Mitogen-activated protein kinase (MAP-K) activation was quantified by Western blotting with an antibody to its phosphorylated substrate, Elk-1. Chemotaxis was evaluated by using a microchemotaxis chamber. SMC fibronectin was measured by Western blotting. For all experiments, PKCalpha was blocked with a selective inhibitor, Gö6976.

RESULTS

Gö6976, at concentrations that allow selective inhibition of PKCalpha, inhibited platelet-derived growth factor-stimulated SMC proliferation and MAP-K activation by 30% to 40% and 30% to 60%, respectively. SMC chemotaxis was stimulated approximately 2-fold by the PKCalpha inhibitor. Neither basal nor transforming growth factor-betaI induced fibronectin production was affected by Gö6976.

CONCLUSIONS

Our data suggest that PKCalpha is a positive mediator of SMC proliferation and MAP-K activity, a negative regulator of migration and has no effect on SMC fibronectin production. These data suggest that modulating activities of specific PKC isotypes might be useful in both the study and control of intimal hyperplasia.

Inhibition of phosphatidylinositol 3-kinase and protein kinase C attenuates extracellular matrix protein-induced vascular smooth muscle cell chemotaxis

PURPOSE

Intimal hyperplasia (IH), a significant cause of vascular reconstructive failure, is characterized by abnormal vascular smooth muscle cell (VSMC) migration, proliferation, and extracellular matrix (ECM) deposition. The ECM proteins, thrombospondin-1 (TSP-1), fibronectin (Fn), and vitronectin (Vn) can induce VSMC migration; however, the cellular signaling pathways involved are not identical for each ECM protein. Phosphatidylinositol 3-kinase (PI3K) and protein kinase C (PKC) are two enzymes that have been associated with VSMC migration. We sought to elucidate the roles of these enzymes in TSP-1-, Fn-, and Vn-stimulated VSMC migration.

METHODS

Chemotaxis assays were performed by using a modified Boyden Chamber. TSP-1, Fn, or Vn (20 microg/mL) or serum-free media (SFM) was placed in the bottom wells of the chamber. Quiescent bovine aortic VSMC were preincubated with LY 294002 (100 micromol/L), a PI3K inhibitor, bisindolylmaleimide I (GF 109203X, 1 micromol/L), a PKC inhibitor, or in SFM alone for 30 minutes. VSMCs (50,000 cells per well) were then placed in the top wells of the chamber, and the assay was conducted for 4 hours at 37 degrees C. Results were recorded as the number of cells migrated per five fields (400x) and analyzed by means of the paired t test, with P value less than.05 considered to be significant (n = 3).

RESULTS

The VSMC migration was significantly increased by TSP-1, Fn, and Vn. LY 294002 inhibited TSP-1-, Fn-, and Vn-stimulated VSMC migration (85% to 89%, P <.05). GF 109203X inhibited only TSP-1-stimulated migration (65%, P <.05).

CONCLUSION

These results suggest that TSP-1-, Fn-, and Vn-stimulated migration is at least partially dependent on PI3K. However, only TSP-1 stimulated migration is at least partially dependent on PKC.