Inhibition of MMP-2 expression affects metabolic enzyme expression levels: proteomic analysis of rat cardiomyocytes

N-Terminomic Identification of Intracellular MMP-2 Substrates in Cardiac Tissue

Proteases are enzymes that induce irreversible post-translational modifications by hydrolyzing amide bonds in proteins. One of these proteases is matrix metalloproteinase-2 (MMP-2), which has been shown to modulate extracellular matrix remodeling and intracellular proteolysis during myocardial injury. However, the substrates of MMP-2 in heart tissue are limited, and lesser known are the cleavage sites. Here, we used degradomics to investigate the substrates of intracellular MMP-2 in rat ventricular extracts. First, we designed a novel, constitutively active MMP-2 fusion protein (MMP-2-Fc) that we expressed and purified from mammalian cells. Using this protease, we proteolyzed ventricular extracts and used subtiligase-mediated N-terminomic labeling which identified 95 putative MMP-2-Fc proteolytic cleavage sites using mass spectrometry. The intracellular MMP-2 cleavage sites identified in heart tissue extracts were enriched for proteins primarily involved in metabolism, as well as the breakdown of fatty acids and amino acids. We further characterized the cleavage of three of these MMP-2-Fc substrates based on the gene ontology analysis. We first characterized the cleavage of sarco/endoplasmic reticulum calcium ATPase (SERCA2a), a known MMP-2 substrate in myocardial injury. We then characterized the cleavage of malate dehydrogenase (MDHM) and phosphoglycerate kinase 1 (PGK1), representing new cardiac tissue substrates. Our findings provide insights into the intracellular substrates of MMP-2 in cardiac cells, suggesting that MMP-2 activation plays a role in cardiac metabolism.

Paradoxical effect of fat diet in matrix metalloproteinases induced mitochondrial dysfunction in diabetic cardiomyopathy

AIMS

Diabetic cardiomyopathy represents the main cause of death among diabetic people. Despite this evidence, the molecular mechanisms triggered by impaired glucose and lipid metabolism inducing heart damage remain unclear. The aim of our study was to investigate the effect of altered metabolism on the early stages of cardiac injury in experimental diabetes.

METHODS

For this purpose, rats were fed a normocaloric diet (NPD) or a high fat diet (HFD) for up to 12 weeks. After the fourth week, streptozocin (35 mg/kg) was administered in a subgroup of both NPD and HFD rats to induce diabetes. Cardiac function was analysed by echocardiography. Matrix metalloproteinases (MMPs) activity and intracellular localization were assessed through zymography and immunofluorescence, whereas apoptotic and oxidative markers by immunohistochemistry and western blot.

RESULTS

Hyperglycaemia or hyperlipidaemia reduced ejection fraction and fractional shortening as compared with control. Unexpectedly, cardiac dysfunction was less marked in diabetic rats fed a hyperlipidaemic diet, suggesting an adaptive response of the myocardium to hyperglycaemia-induced injury. This response was characterized by the inhibition of N-terminal truncated-MMP-2 translocation from endoplasmic reticulum into mitochondria and by superoxide anion overproduction observed in cardiomyocytes under hyperglycaemia.

CONCLUSION

Overall, these findings suggest novel therapeutic targets aimed to counteract mitochondrial dysfunction in the onset of diabetic cardiomyopathy.

Multifunctional intracellular matrix metalloproteinases: implications in disease

Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that were first discovered as proteases, which target and cleave extracellular proteins. During the past 20 years, however, intracellular roles of MMPs were uncovered and research on this new aspect of their biology expanded. MMP-2 is the first of this protease family to be reported to play a crucial intracellular role where it cleaves several sarcomeric proteins inside cardiac myocytes during oxidative stress-induced injury. Beyond MMP-2, currently at least eleven other MMPs are known to function intracellularly including MMP-1, MMP-3, MMP-7, MMP-8, MMP-9, MMP-10, MMP-11, MMP-12, MMP-14, MMP-23 and MMP-26. These intracellular MMPs are localized to different compartments inside the cell including the cytosol, sarcomere, mitochondria, and the nucleus. Intracellular MMPs contribute to the pathogenesis of various diseases. Cardiovascular renal disorders, inflammation, and malignancy are some examples. They also exert antiviral and bactericidal effects. Interestingly, MMPs can act intracellularly through both protease-dependent and protease-independent mechanisms. In this review, we will highlight the intracellular mechanisms of MMPs activation, their numerous subcellular locales, substrates, and roles in different pathological conditions. We will also discuss the future direction of MMP research and the necessity to exploit the knowledge of their intracellular targets and actions for the design of targeted inhibitors.

Tissue Expression of Atrial and Ventricular Myosin Light Chains in the Mechanism of Adaptation to Oxidative Stress

Ischemia/reperfusion (I/R) injury induces post-translational modifications of myosin light chains (MLCs), increasing their susceptibility to degradation by matrix metalloproteinase 2 (MMP-2). This results in the degradation of ventricular light chains (VLC1) in heart ventricles. The aim of the study was to investigate changes in MLCs content in the mechanism of adaptation to oxidative stress during I/R. Rat hearts, perfused using the Langendorff method, were subjected to I/R. The control group was maintained in oxygen conditions. Lactate dehydrogenase (LDH) activity and reactive oxygen/nitrogen species (ROS/RNS) content were measured in coronary effluents. Atrial light chains (ALC1) and ventricular light chains (VLC1) gene expression were examined using RQ-PCR. ALC1 and VLC1 protein content were measured using ELISA tests. MMP-2 activity was assessed by zymography. LDH activity as well as ROS/RNS content in coronary effluents was higher in the I/R group (p = 0.01, p = 0.04, respectively), confirming heart injury due to increased oxidative stress. MMP-2 activity in heart homogenates was also higher in the I/R group (p = 0.04). ALC1 gene expression and protein synthesis were significantly increased in I/R ventricles (p < 0.01, 0.04, respectively). VLC1 content in coronary effluents was increased in the I/R group (p = 0.02), confirming the increased degradation of VLC1 by MMP-2 and probably an adaptive production of ALC1 during I/R. This mechanism of adaptation to oxidative stress led to improved heart mechanical function.

Comprehensive proteomics and functional annotation of mouse brown adipose tissue

Knowledge about the mouse brown adipose tissue (BAT) proteome can provide a deeper understanding of the function of mammalian BAT. Herein, a comprehensive analysis of interscapular BAT from C57BL/6J female mice was conducted by 2DLC and high-resolution mass spectrometry to construct a comprehensive proteome dataset of mouse BAT proteins. A total of 4949 nonredundant proteins were identified, and 4495 were quantified using the iBAQ method. According to the iBAQ values, the BAT proteome was divided into high-, middle- and low-abundance proteins. The functions of the high-abundance proteins were mainly related to glucose and fatty acid oxidation to produce heat for thermoregulation, while the functions of the middle- and low-abundance proteins were mainly related to protein synthesis and apoptosis, respectively. Additionally, 497 proteins were predicted to have signal peptides using SignalP4 software, and 75 were confirmed in previous studies. This study, for the first time, comprehensively profiled and functionally annotated the BAT proteome. This study will be helpful for future studies focused on biomarker identification and BAT molecular mechanisms.

Effects of LY294002 on the function of retinal endothelial cell in vitro

AIM

To study the effects of LY294002 [phosphatidylinositol 3-kinase (PI3K) inhibitor] on the function and mechanisms of retinal endothelial cells (RECs) in vitro.

METHODS

RECs were randomly divided into control group and LY294002 treatment group. RECs in the control group were placed the incubator for hypoxic exposure in vitro. RECs in the LY294002 treatment group were pretreated with LY294002 (40 µmol/L) under hypoxic condition. The expression of matrix metalloproteinase (MMP)-2, MMP-9, vascular endothelial growth factor (VEGF), and apoptosis and proliferation of RECs were evaluated with Western blot, real-time reverse transcription-polymerase chain reaction (RT-PCR), and flow cytometric analysis, correspondently.

RESULTS

Compared with the control group, treating the RECs with LY294002 was able to remarkably inhibit cell proliferation rates (t_1d=2.13, t_2d=2.65, t_3d=2.36, t_4d=2.06, all P<0.05). Flow cytometric analysis indicated that a moderate increase in apoptosis in the LY294002 treatment group compared to the control group (t=2.51, P<0.05). The expression of MMP-2, MMP-9 and VEGF were downregulated in the LY294002 treatment group by Western blot and real-time RT-PCR (all P<0.05).

CONCLUSION

LY294002 regulates the function of RECs by reducing the expression of MMP-2, MMP-9, and VEGF in vitro. LY294002 may provide an effective method for preventing pathological angiogenesis.

Integrated SWATH-based and targeted-based proteomics provide insights into the retinal emmetropization process in guinea pig

Myopia is generally regarded as a failure of normal emmetropization process, however, its underlying molecular mechanisms are unclear. To investigate the retinal protein profile changes during emmetropization, we studied differential protein expressions of ocular growth in young guinea pigs at 3 and 21 days old respectively, when significant axial elongation was detected (P < 0.001, n = 10). Independent pooled retinal samples of both eyes were subjected to SWATH mass spectrometry (MS) followed by bioinformatics analysis using cloud-based platforms. A comprehensive retina SWATH ion-library consisting of 3138 (22,871) unique proteins (peptides) at 1% FDR was constructed. 40 proteins were found to be significantly up-regulated and 8 proteins down-regulated during emmetropization (≥log2 of 0.43 with ≥2 peptides matched per protein; P < 0.05). Using pathway analysis, the most significant pathway identifiable was 'phototransduction' (P = 1.412e-4). Expression patterns of 7 proteins identified in this pathway were further validated and confirmed (P < 0.05) with high-resolution Multiple Reaction Monitoring (MRM-HR) MS. Combining discovery and targeted proteomics approaches, this study for the first time comprehensively profiled protein changes in the guinea pig retina during normal emmetropization-associated eye growth. The findings of this study are also relevant to the myopia development, which is the result of failed emmetropization.

SIGNIFICANCE

Myopia is considered as a failure of emmetropization. However, the underlying biochemical mechanism of emmetropization, a visually guided process in which eye grows towards the optimal optical state of clear vision during early development, is not well understood. Retina is known as the key tissue to regulate this active eye growth. we studied eye growth of young guinea pigs and harvested their retinal tissues. A comprehensive SWATH ion library with identification of a total 3138 unique proteins were established, in which 48 proteins exhibited significant differential expressions between 3 and 21 days old. After MRM-HR confirmation, 'phototransduction' were found as the most active pathway during emmetropic eye growth. This study is the first in discovering key retinal protein players and pathways which are presumably orchestrated by biological mechanism(s) underlying emmetropization.

An intracellular matrix metalloproteinase-2 isoform induces tubular regulated necrosis: implications for acute kidney injury

Acute kidney injury (AKI) causes severe morbidity, mortality, and chronic kidney disease (CKD). Mortality is particularly marked in the elderly and with preexisting CKD. Oxidative stress is a common theme in models of AKI induced by ischemia-reperfusion (I-R) injury. We recently characterized an intracellular isoform of matrix metalloproteinase-2 (MMP-2) induced by oxidative stress-mediated activation of an alternate promoter in the first intron of the MMP-2 gene. This generates an NH₂-terminal truncated MMP-2 (NTT-MMP-2) isoform that is intracellular and associated with mitochondria. The NTT-MMP-2 isoform is expressed in kidneys of 14-mo-old mice and in a mouse model of coronary atherosclerosis and heart failure with CKD. We recently determined that NTT-MMP-2 is induced in human renal transplants with delayed graft function and correlated with tubular cell necrosis. To determine mechanism(s) of action, we generated proximal tubule cell-specific NTT-MMP-2 transgenic mice. Although morphologically normal at the light microscopic level at 4 mo, ultrastructural studies revealed foci of tubular epithelial cell necrosis, the mitochondrial permeability transition, and mitophagy. To determine whether NTT-MMP-2 expression enhances sensitivity to I-R injury, we performed unilateral I-R to induce mild tubular injury in wild-type mice. In contrast, expression of the NTT-MMP-2 isoform resulted in a dramatic increase in tubular cell necrosis, inflammation, and fibrosis. NTT-MMP-2 mice had enhanced expression of innate immunity genes and release of danger-associated molecular pattern molecules. We conclude that NTT-MMP-2 "primes" the kidney to enhanced susceptibility to I-R injury via induction of mitochondrial dysfunction. NTT-MMP-2 may be a novel AKI treatment target.

Fibrosis and Fibrotic Gene Expression in Pediatric and Adult Patients With Idiopathic Dilated Cardiomyopathy

BACKGROUND

Although fibrosis seems to be prognostic for adverse outcomes in adults with idiopathic dilated cardiomyopathy (IDC), little is known about the prevalence and development of fibrosis in pediatric IDC hearts. We hypothesized that there is less activation of fibrosis at a molecular level in pediatric IDC hearts than in failing adult hearts.

METHODS AND RESULTS

Pediatric hearts were analyzed histologically to determine the prevalence of fibrosis. Left ventricular tissue from adult and pediatric IDC hearts and adult and pediatric nonfailing (NF) hearts were subjected to quantitative reverse-transcription polymerase chain reaction to study the expression of important mRNAs that affect fibrosis. We found age-specific differences between IDC and NF hearts in the regulation of noncoding galectin-3, Corin, matrix metalloproteinase (MMP) 2, MMP-9, tissue inhibitor of metalloproteinase (TIMP) 2, and TIMP-3. We also found markers that were similarly altered in both adult and pediatric IDC hearts (interleukin-1 receptor-like 1 receptor, TIMP-1, and TIMP-4). Finally, microRNAs 29a-c were significantly decreased in the pediatric IDC patients.

CONCLUSIONS

Pediatric IDC patients demonstrate age-specific differences in the molecular pathways implicated in fibrosis in the adult heart. At the ultrastructural level the unique gene expression pattern appears to limit fibrosis in the failing pediatric heart.