Jens W. Fischer

Reduced MMP-2 activity contributes to cardiac fibrosis in experimental diabetic cardiomyopathy

ObjectiveTo evaluate the regulation of matrix metalloproteinase (MMP)-2 in diabetic cardiomyopathy.MethodsLeft ventricle (LV) function was determined by a micro-tip catheter in streptozotocin (STZ)-induced diabetic rats, 2 or 6 weeks (w) after STZ-application. LV total collagen, collagen type I and III content were immunohistologically analyzed and quantified by digital image analysis. LV collagen type I, III and MMP-2 mRNA expression was quantified by real-time RT-PCR. LV pro- and active MMP-2 levels were analyzed by zymography; Smad 7, membrane type (MT)1-MMP and tissue inhibitor metalloproteinase (TIMP)-2 protein levels by Western Blot.ResultsSTZ-induced diabetes was associated with a time-dependent impairment of LV diastolic and systolic function. This was paralleled by a time-dependent increase in LV total collagen content, despite reduced LV collagen type I and III mRNA levels, indicating a role of post-transcriptional/post-translational changes of extracellular matrix regulation. Six weeks (w) after STZ-injection, MMP-2 mRNA expression and pro-MMP-2 levels were 2.7-fold (P < 0.005) and 1.3-fold (P < 0.05) reduced versus controls, respectively, whereas active MMP-2 was decreased to undetectable levels 6 w post-STZ. Concomitantly, Smad 7 and TIMP-2 protein levels were 1.3-fold (P < 0.05) and 10-fold (P < 0.005) increased in diabetics versus controls, respectively, whereas the 45 kDa form of MT1-MMP was undetectable in diabetics.ConclusionUnder STZ-diabetic conditions, cardiac fibrosis is associated with a dysregulation in extracellular matrix degradation. This condition is featured by reduced MMP-2 activity, concomitant with increased Smad 7 and TIMP-2 and decreased MT1-MMP protein expression, which differs from mechanisms involved in dilated and ischemic heart disease.

Epidermal EGFR Controls Cutaneous Host Defense and Prevents Inflammation

Epidermal EGFR regulates skin inflammation and contributes to skin barrier function and host defense. Skin-Deep Search for the Effects of EGFR Inhibitors The goal of all medical interventions is to treat disease while minimizing the damage to healthy tissues in the body. This can be difficult to achieve for cancer drugs, however, especially when the effectiveness of a drug directly correlates with its side effects, as is the case for inhibitors of the epidermal growth factor receptor (EGFR). EGFR inhibitors are particularly known for causing a severe rash and skin damage, which sometimes forces patients to prematurely stop their treatments. Now, two papers by Mascia et al. and Lichtenberger et al. help clarify the mechanism of rash formation induced by EGFR inhibitors and uncover some of the skin components that contribute to this phenomenon. Both sets of authors used mouse models that lack EGFR only in the skin to replicate the pattern of injury seen in patients treated with EGFR inhibitors. They characterized the changes in chemokine expression in the skin of treated patients and study animals and examined the effects of EGFR inhibition on skin defenses and bacteria. They also investigated the effects of crossing mice that lack EGFR in the skin with mice deficient in different immune pathways and immune cell types to determine which ones are necessary for the rash phenotype. The findings of these two studies suggest that EGFR signaling is important for normal skin barrier function and antimicrobial defense, and that skin macrophages may contribute to the adverse effects of EGFR inhibitors. Additional work will be necessary to further expand our understanding of EGFR inhibitor toxicity and to continue the search for ways to prevent this disruptive side effect. The current studies provide mechanistic insights that should help guide further investigation in this area. The epidermal growth factor receptor (EGFR) plays an important role in tissue homeostasis and tumor progression. However, cancer patients treated with EGFR inhibitors (EGFRIs) frequently develop acneiform skin toxicities, which are a strong predictor of a patient’s treatment response. We show that the early inflammatory infiltrate of the skin rash induced by EGFRI is dominated by dendritic cells, macrophages, granulocytes, mast cells, and T cells. EGFRIs induce the expression of chemokines (CCL2, CCL5, CCL27, and CXCL14) in epidermal keratinocytes and impair the production of antimicrobial peptides and skin barrier proteins. Correspondingly, EGFRI-treated keratinocytes facilitate lymphocyte recruitment but show a considerably reduced cytotoxic activity against Staphylococcus aureus. Mice lacking epidermal EGFR (EGFRΔep) show a similar phenotype, which is accompanied by chemokine-driven skin inflammation, hair follicle degeneration, decreased host defense, and deficient skin barrier function, as well as early lethality. Skin toxicities were not ameliorated in a Rag2-, MyD88-, and CCL2-deficient background or in mice lacking epidermal Langerhans cells. The skin phenotype was also not rescued in a hairless (hr/hr) background, demonstrating that skin inflammation is not induced by hair follicle degeneration. Treatment with mast cell inhibitors reduced the immigration of T cells, suggesting that mast cells play a role in the EGFRI-mediated skin pathology. Our findings demonstrate that EGFR signaling in keratinocytes regulates key factors involved in skin inflammation, barrier function, and innate host defense, providing insights into the mechanisms underlying EGFRI-induced skin pathologies.

Biglycan Is Required for Adaptive Remodeling After Myocardial Infarction

Background— After myocardial infarction (MI), extensive remodeling of extracellular matrix contributes to scar formation and preservation of hemodynamic function. On the other hand, adverse and excessive extracellular matrix remodeling leads to fibrosis and impaired function. The present study investigates the role of the small leucine-rich proteoglycan biglycan during cardiac extracellular matrix remodeling and cardiac hemodynamics after MI. Methods and Results— Experimental MI was induced in wild-type (WT) and bgn−/0 mice by permanent ligation of the left anterior descending coronary artery. Biglycan expression was strongly increased at 3, 7, and 14 days after MI in WT mice. bgn−/0 mice showed increased mortality rates after MI as a result of frequent left ventricular (LV) ruptures. Furthermore, tensile strength of the LV derived from bgn−/0 mice 21 days after MI was reduced as measured ex vivo. Collagen matrix organization was severely impaired in bgn−/0 mice, as shown by birefringence analysis of Sirius red staining and electron microscopy of collagen fibrils. At 21 days after MI, LV hemodynamic parameters were assessed by pressure-volume measurements in vivo to obtain LV end-diastolic pressure, end-diastolic volume, and end-systolic volume. bgn−/0 mice were characterized by aggravated LV dilation evidenced by increased LV end-diastolic volume (bgn−/0, 111±4.2 &mgr;L versus WT, 96±4.4 &mgr;L; P<0.05) and LV end-diastolic pressure (bgn−/0, 24±2.7 versus WT, 18±1.8 mm Hg; P<0.05) and severely impaired LV function (EF, bgn−/0, 12±2% versus WT, 21±4%; P<0.05) 21 days after MI. Conclusion— Biglycan is required for stable collagen matrix formation of infarct scars and for preservation of cardiac hemodynamic function.

Survivin Determines Cardiac Function by Controlling Total Cardiomyocyte Number

Background— Survivin inhibits apoptosis and regulates cell division in many organs, but its function in the heart is unknown. Methods and Results— We show that cardiac-specific deletion of survivin resulted in premature cardiac death. The underlying cause was a dramatic reduction in total cardiomyocyte numbers as determined by a stereological method for quantification of cells per organ. The resulting increased hemodynamic load per cell led to progressive heart failure as assessed by echocardiography, magnetic resonance imaging, positron emission tomography, and invasive catheterization. The reduction in total cardiomyocyte number in α-myosin heavy chain (MHC)–survivin−/− mice was due to an ≈50% lower mitotic rate without increased apoptosis. This occurred at the expense of DNA accumulation because survivin-deficient cardiomyocytes displayed marked DNA polyploidy indicative of consecutive rounds of DNA replication without cell division. Survivin small interfering RNA knockdown in neonatal rat cardiomyocytes also led to polyploidization and cell cycle arrest without apoptosis. Adenoviral overexpression of survivin in cardiomyocytes inhibited doxorubicin-induced apoptosis, induced DNA synthesis, and promoted cell cycle progression. The phenotype of the αMHC-survivin−/− mice also allowed us to determine the minimum cardiomyocyte number sufficient for normal cardiac function. In human cardiomyopathy, survivin was potently induced in the failing heart and downregulated again after hemodynamic support by a left ventricular assist device. Its expression positively correlated with the mean cardiomyocyte DNA content. Conclusions— We suggest that the ontogenetically determined cardiomyocyte number may be an independent factor in the susceptibility to cardiac diseases. Through its profound impact on both cardiomyocyte replication and apoptosis, survivin may emerge as a promising new target for myocardial regeneration.

Regulation of Thrombomodulin Expression in Human Vascular Smooth Muscle Cells by COX-2–Derived Prostaglandins

There is concern that cyclooxygenase (COX)-2 inhibitors may promote atherothrombosis by inhibiting vascular formation of prostacyclin (PGI2) and an increased thrombotic risk of COX-2 inhibitors has been reported. It is widely accepted that the prothrombotic effects of COX-2 inhibitors can be explained by the removal of platelet-inhibitory PGI2. Using microarray chip technology, we have previously demonstrated that thrombomodulin (TM) mRNA is upregulated in cultured human coronary artery smooth muscle cells by the stable prostacyclin mimetic iloprost. This study is the first to demonstrate a stimulation of the expression of functionally active thrombomodulin in human smooth muscle cells by prostaglandins, endogenously formed via the COX-2 pathway. Because TM is an important inhibitor of blood coagulation, these findings provide a novel platelet-independent mechanism to explain the prothrombotic effects of COX-2 inhibitors. The full text of this article is available online at http://circres.ahajournals.org.

Inhibition of Hyaluronan Synthesis Accelerates Murine Atherosclerosis Novel Insights Into the Role of Hyaluronan Synthesis

Background— Hyaluronan is thought to mediate neointimal hyperplasia but also vasoprotection as an integral component of the endothelial glycocalyx. The present study addressed for the first time the effects of long-term pharmacological inhibition of hyaluronan synthesis on vascular function and atherosclerosis. Methods and Results— Four-week-old apolipoprotein E–deficient mice on a Western diet received orally an inhibitor of hyaluronan synthesis, 4-methylumbelliferone (4-MU; 10 mg/g body wt), resulting in 600 nmol/L 4-MU in plasma. As a result, aortic plaque burden was markedly increased at 25 weeks. Furthermore, acetylcholine-dependent relaxation of aortic rings was decreased and mean arterial blood pressure was increased in response to 4-MU. However, hydralazine blunted the hypertensive effect of 4-MU without inhibiting the proatherosclerotic effect. A photothrombosis model revealed a prothrombotic state that was not due to increased platelet activation or increased thrombin activation as monitored by CD62P expression and the endogenous thrombin potential. Importantly, increased recruitment of macrophages to vascular lesions was detected after 2 and 21 weeks of 4-MU treatment by immunohistochemistry, by intravital microscopy, and in a peritonitis model. As a potential underlying mechanism, severe damage of the endothelial glycocalyx after 2 and 21 weeks of treatment with 4-MU was detected by electron microscopy of the innominate artery and myocardial capillaries. Furthermore, 600 nmol/L 4-MU inhibited hyaluronan synthesis in cultured endothelial cells. Conclusions— The data suggest that systemic inhibition of hyaluronan synthesis by 4-MU interferes with the protective function of the endothelial glycocalyx, thereby facilitating leukocyte adhesion, subsequent inflammation, and progression of atherosclerosis.Background— Hyaluronan is thought to mediate neointimal hyperplasia but also vasoprotection as an integral component of the endothelial glycocalyx. The present study addressed for the first time the effects of long-term pharmacological inhibition of hyaluronan synthesis on vascular function and atherosclerosis. Methods and Results— Four-week-old apolipoprotein E–deficient mice on a Western diet received orally an inhibitor of hyaluronan synthesis, 4-methylumbelliferone (4-MU; 10 mg/g body wt), resulting in 600 nmol/L 4-MU in plasma. As a result, aortic plaque burden was markedly increased at 25 weeks. Furthermore, acetylcholine-dependent relaxation of aortic rings was decreased and mean arterial blood pressure was increased in response to 4-MU. However, hydralazine blunted the hypertensive effect of 4-MU without inhibiting the proatherosclerotic effect. A photothrombosis model revealed a prothrombotic state that was not due to increased platelet activation or increased thrombin activation as monitored by CD62P expression and the endogenous thrombin potential. Importantly, increased recruitment of macrophages to vascular lesions was detected after 2 and 21 weeks of 4-MU treatment by immunohistochemistry, by intravital microscopy, and in a peritonitis model. As a potential underlying mechanism, severe damage of the endothelial glycocalyx after 2 and 21 weeks of treatment with 4-MU was detected by electron microscopy of the innominate artery and myocardial capillaries. Furthermore, 600 nmol/L 4-MU inhibited hyaluronan synthesis in cultured endothelial cells. Conclusions— The data suggest that systemic inhibition of hyaluronan synthesis by 4-MU interferes with the protective function of the endothelial glycocalyx, thereby facilitating leukocyte adhesion, subsequent inflammation, and progression of atherosclerosis. # Clinical Perspective {#article-title-39}

Induction of hyaluronic acid synthase 2 (HAS2) in human vascular smooth muscle cells by vasodilatory prostaglandins.

Abstract— Hyaluronic acid (HA) is a prominent constituent of the extracellular matrix of atherosclerotic vascular lesions in humans known to modulate vascular smooth muscle phenotype. The regulation of HA synthesis by vasodilatory prostaglandins was analyzed in human arterial smooth muscle cells (SMCs). The prostacyclin analogue, iloprost (100 nmol/L), markedly increased pericellular formation of HA coats and HA secretion into the cell culture medium in human arterial SMCs (8.7±1.6-fold). Expression of HA synthase 2 (HAS2) was determined by semiquantitative RT-PCR and found to be strongly upregulated at concentrations of iloprost between 1 and 100 nmol/L after 3 hours. Furthermore, endogenous cyclooxygenase-2 (COX2) activity was required for basal expression of HAS2 mRNA in SMCs in vitro. Total HA secretion in response to iloprost was markedly decreased by RNA interference (RNAi), specific for HAS2. In addition, siRNA targeting HAS2 strongly increased the spreading of human SMCs compared with mock-transfected cells. HAS2 mRNA levels were also stimulated by a selective prostacyclin receptor (IP) agonist, cicaprost (10 nmol/L), prostaglandin E2 (10 nmol/L), and the EP2 receptor agonist, butaprost (1 &mgr;mol/L). Induction of HAS2 mRNA and HA synthesis by prostaglandins was mimicked by stable cAMP analogues and forskolin. In human atherectomy specimens from the internal carotid artery, HA deposits and COX2 expression colocalized frequently. In addition, strong EP2 receptor expression was detected in SMCs in HA-rich areas. Therefore, upregulation of HAS2 expression via EP2 and IP receptors might contribute to the accumulation of HA during human atherosclerosis, thereby mediating proatherosclerotic functions of COX2.

Decorin Promotes Aortic Smooth Muscle Cell Calcification and Colocalizes to Calcified Regions in Human Atherosclerotic Lesions

Objective—Ectopic calcification localized to the intima of atherosclerotic plaque is a risk marker for cardiovascular events and increases the risk of aortic dissection during angioplasty. A variety of extracellular matrix molecules such as collagen type 1, bone sialoprotein, and osteopontin are known to regulate the biomineralization of bone and ectopic vascular calcification. In the present study, it was investigated whether decorin, a small leucine-rich proteoglycan expressed in bone and atherosclerotic plaque, is involved in arterial calcification. Methods and ResultsCalcification was induced in cultured bovine aortic smooth muscle cell (BASMC) by the addition of β-glycerophosphate or inorganic phosphate. Northern and Western analysis revealed that decorin expression was strongly upregulated in mineralizing BASMC. Furthermore, overexpression of decorin using a retroviral expression vector resulted in a 3- to 4-fold elevation of calcium deposited on the BASMC monolayer. Increased calcification in response to decorin could also be mimicked by adding exogenous decorin to the cultures. In addition, human coronary atherosclerotic lesions taken from sudden-death patients showed marked colocalization of calcium deposits with decorin. Conclusions—Decorin induces calcification of arterial smooth muscle cell cultures and colocalizes to mineral deposition in human atherosclerotic plaque, suggesting that decorin functions as promoter of intimal calcification.

Retroviral Overexpression of Decorin Differentially Affects the Response of Arterial Smooth Muscle Cells to Growth Factors

Abstract—Decorin is a member of the family of small leucine-rich proteoglycans that are present in blood vessels and synthesized by arterial smooth muscle cells (ASMCs). This proteoglycan accumulates in topographically defined regions of atherosclerotic lesions and may play a role in the development of this disease. However, little is known about whether decorin has specific effects on the cellular events that contribute to atherosclerotic lesion formation. In the present study, rat ASMCs were transduced with a retroviral vector (LDSN) that carries the bovine decorin gene. Compared with vector control cells (LXSN), these cells constitutively overexpress decorin, as verified by Northern and Western analysis and by metabolic labeling. Experiments were performed to examine the responsiveness of decorin-overexpressing rat ASMCs to platelet-derived growth factor (PDGF) and transforming growth factor-&bgr;1 (TGF-&bgr;1), 2 growth factors that affect cell proliferation and extracellular matrix production in atherosclerosis. Decorin-overexpressing cells had decreased [3H]thymidine incorporation into DNA and increased the levels of the cyclin-dependent kinase inhibitors p21 and p27 in the first 24 hours of response to serum and PDGF-BB. However, these effects of decorin were not apparent at 48 or 72 hours after plating and did not result in reduced growth of decorin-overexpressing cells in response to serum and PDGF-BB. In contrast, the growth response of decorin-overexpressing ASMCs to TGF-&bgr;1, as well as the expression of TGF-&bgr;1–responsive genes, such as plasminogen activator inhibitor-1 and versican (an extracellular matrix proteoglycan), was diminished. These results indicate that decorin selectively inhibits the responsiveness of rat ASMCs to TGF-&bgr;1 and suggests that the induction of constitutive decorin overexpression by ASMCs in vivo may have therapeutic value in the inhibition of TGF-&bgr;1–mediated effects on the development of atherosclerotic lesions.

Collagen Fragments Inhibit Hyaluronan Synthesis in Skin Fibroblasts in Response to Ultraviolet B (UVB): NEW INSIGHTS INTO MECHANISMS OF MATRIX REMODELING*

UVB irradiation causes characteristic features of skin aging including remodeling of the dermal extracellular matrix. A key feature during this process is the up-regulation of matrix metalloproteinases and cleavage of collagen. Hyaluronic acid (HA), a major component of the dermal matrix, decreases after chronic UVB exposure. However, the factors that govern the decline of HA synthesis during the course of actinic aging are largely unknown. The aim of the present study was to explore whether collagen degradation causes inhibition of HA synthesis in human skin fibroblasts. After treatment of fibroblasts with collagen fragments (CF) in vitro, resolution of the actin cytoskeleton and inhibition of HA secretion occurred because of specific down-regulation of hyaluronan synthase 2 (HAS2) expression. The αvβ3-agonist, RGDS, latrunculin A, and an inhibitor of Rho-activated kinase inhibited HAS2 expression. Conversely, blocking antibodies to αvβ3 abolished the down-regulation of HAS2 and the cytoskeletal effects. Furthermore, inhibition of cofilin phosphorylation in response to CF was prevented by αvβ3-blocking antibodies. The key role of ERK signaling was shown by reduced nuclear accumulation of phosphoERK and of ELK-1 phosphorylation in response to CF. In addition, the ERK inhibitor PD98059 reduced HAS2 expression. Also, UVB irradiation of fibroblasts caused down-regulation of HAS2, which was sensitive to matrix metalloproteinase inhibitors and to αvβ3-blocking antibodies. In conclusion, these data suggest that CF activate αvβ3-integrins and in turn inhibit Rho kinase (ROCK) signaling and nuclear translocation of phosphoERK, resulting in reduced HAS2 expression. Therefore, a novel mechanism is presented how proteolytic collagen cleavage may inhibit HA synthesis in dermal fibroblasts during extrinsic skin aging.