Qiuxia Dai

Matrix metalloproteinase-9 deletion attenuates myocardial fibrosis and diastolic dysfunction in ageing mice

AIMS Age-related diastolic dysfunction has been attributed to an increased passive stiffness, which is regulated by extracellular matrix (ECM). We recently showed that matrix metalloproteinase (MMP)-9, an ECM mediator, increases in the left ventricle (LV) with age. The aim of this study, accordingly, was to determine the role of MMP-9 in cardiac ageing. METHODS AND RESULTS We compared LV function in young (6-9 months), middle-aged (12-15 months), old (18-24 months) and senescent (26-34 months) wild-type (WT) and MMP-9 null mice (n ≥ 12/group). All groups had similar fractional shortenings and aortic peak velocities, indicating that systolic function was not altered by ageing or MMP-9 deletion. The mitral ratios of early to late diastolic filling velocities were reduced in old and senescent WT compared with young controls, and this reduction was attenuated in MMP-9 null mice. Concomitantly, the increase in LV collagen content was reduced in MMP-9 null mice (n = 5-6/group). To dissect the mechanisms of these changes, we evaluated the mRNA expression levels of 84 ECM and adhesion molecules by real-time qPCR (n = 6/group). The expression of pro-fibrotic periostin and connective tissue growth factor (CTGF) increased with senescence, as did transforming growth factor-β (TGF-β)-induced protein levels and Smad signalling, and these increases were blunted by MMP-9 deletion. In senescence, MMP-9 deletion also resulted in a compensatory increase in MMP-8. CONCLUSION MMP-9 deletion attenuates the age-related decline in diastolic function, in part by reducing TGF-β signalling-induced periostin and CTGF expression and increasing MMP-8 expression to regulate myocardial collagen turnover and deposition.

Proteomic Analysis Identifies In vivo Candidate Matrix Metalloproteinase-9 Substrates in the Left Ventricle Post-Myocardial Infarction

Matrix metalloproteinase‐9 (MMP‐9) deletion has been shown to improve remodeling of the left ventricle post‐myocardial infarction (MI), but the mechanisms to explain this improvement have not been fully elucidated. MMP‐9 has a broad range of in vitro substrates, but relevant in vivo substrates are incompletely defined. Accordingly, we evaluated the infarct regions of wild‐type (wt) and MMP‐9 null (null) mice using a proteomic strategy. Wt and null groups showed similar infarct sizes (48±3 in wt and 45±3% in null), indicating that both groups received an equal injury stimulus. Left ventricle infarct tissue was homogenized and analyzed by 2‐DE and MS. Of 31 spot intensity differences, the intensities of 9 spots were higher and 22 spots were lower in null mice compared to wt (all p<0.05). Several extracellular matrix proteins were identified in these spots by MS, including fibronectin, tenascin‐C, thrombospondin‐1, and laminin. Fibronectin was observed on the gels at a lower than expected molecular weight in the wt group, which suggested substrate cleavage, and the lower molecular weight spot was observed at lower intensity in the MMP‐9 null group, which suggested cleavage by MMP‐9. Immunoblotting confirmed the presence of fibronectin cleavage products in the wt samples and lower levels in the absence of MMP‐9. In conclusion, examining infarct tissue from wt and MMP‐9 null mice by proteomic analysis provides a powerful and unique method to identify in vivo candidate MMP substrates.

Transgenic overexpression of matrix metalloproteinase-9 in macrophages attenuates the inflammatory response and improves left ventricular function post-myocardial infarction.

Following myocardial infarction (MI), activated macrophages infiltrate into the necrotic myocardium as part of a robust pro-inflammatory response and secrete matrix metalloproteinase-9 (MMP-9). Macrophage activation, in turn, modulates the fibrotic response, in part by stimulating fibroblast extracellular matrix (ECM) synthesis. We hypothesized that overexpression of human MMP-9 in mouse macrophages would amplify the inflammatory and fibrotic responses to exacerbate left ventricular dysfunction. Unexpectedly, at day 5 post-MI, ejection fraction was improved in transgenic (TG) mice (25±2%) compared to the wild type (WT) mice (18±2%; p<0.05). By gene expression profiling, 23 of 84 inflammatory genes were decreased in the left ventricle infarct (LVI) region from the TG compared to WT mice (all p<0.05). Concomitantly, TG macrophages isolated from the LVI, as well as TG peritoneal macrophages stimulated with LPS, showed decreased inflammatory marker expression compared to WT macrophages. In agreement with attenuated inflammation, only 7 of 84 cell adhesion and ECM genes were increased in the TG LVI compared to WT LVI, while 43 genes were decreased (all p<0.05). These results reveal a novel role for macrophage-derived MMP-9 in blunting the inflammatory response and limiting ECM synthesis to improve left ventricular function post-MI.

SPARC mediates early extracellular matrix remodeling following myocardial infarction

Secreted protein, acidic, and rich in cysteine (SPARC) is a matricellular protein that functions in the extracellular processing of newly synthesized collagen. Collagen deposition to form a scar is a key event following a myocardial infarction (MI). Because the roles of SPARC in the early post-MI setting have not been defined, we examined age-matched wild-type (WT; n=22) and SPARC-deficient (null; n=25) mice at day 3 post-MI. Day 0 WT (n=28) and null (n=20) mice served as controls. Infarct size was 52 ± 2% for WT and 47 ± 2% for SPARC null (P=NS), indicating that the MI injury was comparable in the two groups. By echocardiography, WT mice increased end-diastolic volumes from 45 ± 2 to 83 ± 5 μl (P < 0.05). SPARC null mice also increased end-diastolic volumes but to a lesser extent than WT (39 ± 3 to 63 ± 5 μl; P < 0.05 vs. day 0 controls and vs. WT day 3 MI). Ejection fraction fell post-MI in WT mice from 57 ± 2 to 19 ± 1%. The decrease in ejection fraction was attenuated in the absence of SPARC (65 ± 2 to 28 ± 2%). Fibroblasts isolated from SPARC null left ventricle (LV) showed differences in the expression of 22 genes encoding extracellular matrix and adhesion molecule genes, including fibronectin, connective tissue growth factor (CTGF; CCN2), matrix metalloproteinase-3 (MMP-3), and tissue inhibitor of metalloproteinase-2 (TIMP-2). The change in fibroblast gene expression levels was mirrored in tissue protein extracts for fibronectin, CTGF, and MMP-3 but not TIMP-2. Combined, the results of this study indicate that SPARC deletion preserves LV function at day 3 post-MI but may be detrimental for the long-term response due to impaired fibroblast activation.

CC chemokine receptor 5 deletion impairs macrophage activation and induces adverse remodeling following myocardial infarction

Post-myocardial infarction (MI), chemokine homing of inflammatory cells into the injured left ventricle (LV) regulates ventricular remodeling, in part by stimulating the extracellular matrix response. The CC chemokine receptor 5 (CCR5) is a key chemokine receptor expressed on macrophages, and CCR5 ligands are highly upregulated post-MI. We hypothesized that deletion of CCR5 would attenuate adverse remodeling by decreasing inflammatory cell recruitment. Accordingly, we examined LV function, macrophage recruitment and activation, and collagen content in wild-type (WT, n = 25) and CCR5 null (n = 33) mice at 7 days post-MI. Both groups had similar infarct sizes (44 ± 2% in WT and 42 ± 2% in CCR5 null; P = 0.37). However, the LV remodeling index (end diastolic volume/LV mass) increased to a larger extent in CCR5 null (1.28 ± 0.08 μl/mg for CCR5 null and 1.02 ± 0.06 μl/mg for WT; P < 0.05). Although numbers of infiltrated macrophages were similar in WT and CCR5 null mice, CCR5-deficient macrophages isolated from the infarct zone displayed >50% decrease in gene expression levels of proinflammatory activation markers (interleukin-1β, interleukin-6, and tumor necrosis factor-α), as well as anti-inflammatory activation markers (arginase 1, CD163, mannose receptor, and transforming growth factor-β1) compared with WT (all P < 0.05). Concomitant with the reduced macrophage activation, heat shock protein-47 and collagen type I precursor levels in the infarct region decreased in the CCR5 null (1.2 ± 0.3 units in the CCR5 null and 2.3 ± 0.4 units in the WT; P < 0.05), while collagen fragments increased (88.3 ± 5.9 units in the CCR5 null and 32.7 ± 8.5 units in the WT; P < 0.05). We conclude that CCR5 deletion impairs LV remodeling by hindering macrophage activation, which stimulates an imbalance in collagen metabolism and increases the remodeling index.

Texas 3-Step decellularization protocol: Looking at the cardiac extracellular matrix

UNLABELLED The extracellular matrix (ECM) is a critical tissue component, providing structural support as well as important regulatory signaling cues to govern cellular growth, metabolism, and differentiation. The study of ECM proteins, however, is hampered by the low solubility of ECM components in common solubilizing reagents. ECM proteins are often not detected during proteomics analyses using unbiased approaches due to solubility issues and relatively low abundance compared to highly abundant cytoplasmic and mitochondrial proteins. Decellularization has become a common technique for ECM protein-enrichment and is frequently used in engineering studies. Solubilizing the ECM after decellularization for further proteomic examination has not been previously explored in depth. In this study, we describe testing of a series of protocols that enabled us to develop a novel optimized strategy for the enrichment and solubilization of ECM components. Following tissue decellularization, we use acid extraction and enzymatic deglycosylation to facilitate re-solubilization. The end result is the generation of three fractions for each sample: soluble components, cellular components, and an insoluble ECM fraction. These fractions, developed in mass spectrometry-compatible buffers, are amenable to proteomics analysis. The developed protocol allows identification (by mass spectrometry) and quantification (by mass spectrometry or immunoblotting) of ECM components in tissue samples. BIOLOGICAL SIGNIFICANCE The study of extracellular matrix (ECM) proteins in pathological and non-pathological conditions is often hampered by the low solubility of ECM components in common solubilizing reagents. Additionally, ECM proteins are often not detected during global proteomic analyses due to their relatively low abundance compared to highly abundant cytoplasmic and mitochondrial proteins. In this manuscript we describe testing of a series of protocols that enabled us to develop a final novel optimized strategy for the enrichment and solubilization of ECM components. The end result is the generation of three fractions for each sample: soluble components, cellular components, and an insoluble ECM fraction. By analysis of each independent fraction, differences in protein levels can be detected that in normal conditions would be masked. These fractions are amenable to mass spectrometry analysis to identify and quantify ECM components in tissue samples. The manuscript places a strong emphasis on the immediate practical relevance of the method, particularly when using mass spectrometry approaches; additionally, the optimized method was validated and compared to other methodologies described in the literature.

In vivo Matrix Metalloproteinase-7 Substrates Identified in the Left Ventricle Post-Myocardial Infarction Using Proteomics

Matrix metalloproteinase-7 (MMP-7) deletion has been shown to improve survival after myocardial infarction (MI). MMP-7 has a large array of in vitro substrates, but in vivo substrates for MMP-7 following MI have not been fully identified. Accordingly, we evaluated the infarct regions of wild-type (WT; n = 12) and MMP-7 null (null; n = 10) mice using a proteomic strategy. Seven days post-MI, infarct regions of the left ventricles were excised, homogenized, and protein extracts were analyzed by two-dimensional gel electrophoresis and mass spectrometry. Of 13 spots that showed intensity differences between WT and null, the intensities of eight spots were higher and those of five spots were lower in the null group (p < 0.05). Fibronectin and tenascin-C, known in vitro substrates of MMP-7, were identified in spots that showed lower intensity in the null. Immunoblotting and in vitro cleavage assays confirmed reduced fibronectin and tenascin-C fragment generation in the null, and this effect was restored by exogenous administration of MMP-7. Lower levels of full-length peroxiredoxin-1 and -2 and higher levels of the full-length peroxiredoxin-3 were detected in the null group, suggesting MMP-7 deletion may also indirectly regulate protein levels through nonenzymatic mechanisms. In conclusion, this is the first study to identify fibronectin and tenascin-C as in vivo MMP-7 substrates in the infarcted left ventricle using a proteomic approach.

Multi-analyte profiling reveals matrix metalloproteinase-9 and monocyte chemotactic protein-1 as plasma biomarkers of cardiac aging

Background— We have previously shown that cardiac sarcopenia occurs with age in C57/BL6J mice. However, underlying mechanisms and plasma biomarkers of cardiac aging have not been identified. Accordingly, the objective of this study was to identify and evaluate plasma biomarkers that reflect cardiac aging phenotypes. Methods and Results— Plasma from adult (7.5±0.5 months old, n=27) and senescent (31.7±0.5 months old, n=25) C57/BL6J mice was collected, and levels of 69 markers were measured by multi-analyte profiling. Of these, 26 analytes were significantly increased and 3 were significantly decreased in the senescent group compared with the adult group. The majority of analytes that increased in the senescent group were inflammatory markers associated with macrophage functions, including matrix metalloproteinase-9 (MMP-9) and monocyte chemotactic protein-1 (MCP-1/CCL-2). Immunoblotting (n=12/group) showed higher MMP-9 and MCP-1 levels in the left ventricle (LV) of senescent mice (P<0.05), and their expression levels in the LV correlated with plasma levels (&rgr;=0.50 for MMP-9 and &rgr; =0.62 for MCP1, P<0.05). Further, increased plasma MCP-1 and MMP-9 levels correlated with the increase in end-diastolic dimensions that occurs with senescence. Immunohistochemistry (n=3/group) for Mac-3, a macrophage marker, showed increased macrophage densities in the senescent LV, and dual-labeling immunohistochemistry of Mac-3 and MMP-9 revealed robust colocalization of MMP-9 to the macrophages in the senescent LV sections, indicating that the macrophage is a major contributor of MMP-9 in the senescent LV. Conclusions— Our results suggest that MCP-1 and MMP-9 are potential plasma markers for cardiac aging and that augmented MCP-1 and MMP-9 levels and macrophage content in the LV could provide an underlying inflammatory mechanism of cardiac aging.Background —We have previously shown that cardiac sarcopenia occurs with age in C57/BL6J mice. However, underlying mechanisms and plasma biomarkers of cardiac aging have not been identified. Accordingly, the objective of this study was to identify and evaluate plasma biomarkers that reflect cardiac aging phenotypes. Methods and Results —Plasma from adult (7.5±0.5 months old, n=27) and senescent (31.7±0.5 months old, n=25) C57/BL6J mice was collected and levels of 69 markers were measured by multi-analyte profiling. Of these, 26 analytes were significantly increased and 3 were significantly decreased in the senescent group compared to the adult group. The majority of analytes that increased in the senescent group were inflammatory markers associated with macrophage functions, including matrix metalloproteinase-9 (MMP-9) and monocyte chemotactic protein-1 (MCP-1/CCL-2). Immunoblotting (n=12/ group) showed higher MMP-9 and MCP-1 levels in the left ventricle (LV) of senescent mice (p<0.05), and their expression levels in the LV correlated with plasma levels (rho=0.50 for MMP-9 and rho=0.62 for MCP1, p<0.05). Further, increased plasma MCP-1 and MMP-9 levels correlated with the increase in end diastolic dimensions that occurs with senescence. Immunohistochemistry (n=3/ group) for Mac-3, a macrophage marker, showed increased macrophage densities in the senescent LV; and dual labeling immunohistochemistry of Mac-3 and MMP-9 revealed robust co-localization of MMP-9 to the macrophages in the senescent LV sections, indicating that the macrophage is a major contributor of MMP-9 in the senescent LV. Conclusions —Our results suggest that MCP-1 and MMP-9 are potential plasma markers for cardiac aging and that augmented MCP-1 and MMP-9 levels and macrophage content in the LV could provide an underlying inflammatory mechanism of cardiac aging.

The left ventricle proteome differentiates middle-aged and old left ventricles in mice.

Middle-aged and old left ventricles (LVs) are structurally and functionally very similar. Compared to a young LV, both show increased wall thickness and increased cavity size, with preserved cardiac function. However, when a stressor such as myocardial infarction occurs, striking differences are revealed between young and old LVs and there is a marked reduction in survival rates for the old group. The objective of this study was to investigate the proteomic basis of age-related changes in the LV of male mice in order to identify proteins that are differentially expressed between middle-aged and old groups and to gain mechanistic insight into effects of aging on the unstressed heart. Young (3 months old; n = 6), middle-aged (MA; 15 months old; n = 6), and old (23 months old; n = 5) LVs were examined by echocardiography, homogenized, and separated into soluble and insoluble protein fractions using differential extraction. We found that the LV mass-to-tibia ratio increased from 6.4 +/- 0.2 mg/mm in young to 11.0 +/- 0.6 and 10.1 +/- 0.7 mg/mm in MA and old, respectively (both p < 0.05 vs young), which was caused by increases in both LV wall thickness and volume. Using two-dimensional gel electrophoresis, we detected age-related alterations in the levels of 73 proteins (all p < 0.05). Among these proteins were mortalin, peroxiredoxin 3, epoxide hydrolase, and the superoxide dismutases SOD-1 (Cu/ZnSOD) and SOD-2 (MnSOD), which have been previously associated with aging and/or cardiovascular disease. Together, these results reveal proteomic changes that occur in the LV with age. The proteins identified here may be useful markers of cardiac aging and may help in deducing mechanisms to explain the inability of the old heart to withstand challenge.

Combining experimental and mathematical modeling to reveal mechanisms of macrophage-dependent left ventricular remodeling.

BackgroundProgressive remodeling of the left ventricle (LV) following myocardial infarction (MI) can lead to congestive heart failure, but the underlying initiation factors remain poorly defined. The objective of this study, accordingly, was to determine the key factors and elucidate the regulatory mechanisms of LV remodeling using integrated computational and experimental approaches.ResultsBy examining the extracellular matrix (ECM) gene expression and plasma analyte levels in C57/BL6J mice LV post-MI and ECM gene responses to transforming growth factor (TGF-β1) in cultured cardiac fibroblasts, we found that key factors in LV remodeling included macrophages, fibroblasts, transforming growth factor-β1, matrix metalloproteinase-9 (MMP-9), and specific collagen subtypes. We established a mathematical model to study LV remodeling post-MI by quantifying the dynamic balance between ECM construction and destruction. The mathematical model incorporated the key factors and demonstrated that TGF-β1 stimuli and MMP-9 interventions with different strengths and intervention times lead to different LV remodeling outcomes. The predictions of the mathematical model fell within the range of experimental measurements for these interventions, providing validation for the model.ConclusionsIn conclusion, our results demonstrated that the balance between ECM synthesis and degradation, controlled by interactions of specific key factors, determines the LV remodeling outcomes. Our mathematical model, based on the balance between ECM construction and destruction, provides a useful tool for studying the regulatory mechanisms and for predicting LV remodeling outcomes.