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1Cardiovascular Institute, 2Division of Gastroenterology, and 3Center for Biological Imaging, University of Pittsburgh, Pittsburgh, Pennsylvania 15213
Submitted 16 July 2003 ; accepted in final form 6 April 2004
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ABSTRACT |
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receptor-1 (TNFR1)-mediated pathways in a murine model of myocardial infarction and remodeling. One hundred and ninety-four wild-type (WT) and TNFR1 gene-deleted (TNFR1KO) mice underwent left coronary artery ligation to induce myocardial infarction. On days 1, 3, 7, and 42, mice underwent transesophageal echocardiography. Hearts were weighed, and the left ventricle (LV) was assayed for matrix metalloproteinase (MMP)-2 and -9 activity and for tissue inhibitor of MMP (TIMP)-1 and -2 expression. Deletion of the TNFR1 gene substantially improved survival because no deaths were observed in TNFR1KO mice versus 56.4% and 18.2% in WT males and females, respectively (P < 0.002). At 42 days, LV remodeling, assessed by LV function (fractional area change of 31.9 ± 7.9%, 32.2 ± 7.7%, and 21.6 ± 7.1% in TNFR1KO males, TNFR1KO females, and WT females, respectively, P < 0.04), and hypertrophy (heart weight-to-body weight ratios of 5.435 ± 0.986, 5.485 ± 0.677, and 6.726 ± 0.704 mg/g, P < 0.04) were ameliorated in TNFR1KO mice. MMP-9 activity was highest at 3 days postinfarction and was highest in WT males (1.9 ± 0.4 4, 3.6 ± 0.24, 1.15 ± 0.28, and 1.3 ± 1.2 ng/100 µg protein, respectively, in TNFR1KO males, WT males, TNFR1KO females, and WT females, respectively, P < 0.002), whereas at 3 days TIMP-1 mRNA fold upregulation compared with type- and sex-matched controls was lowest in WT males (138.32 ± 13.05, 46.74 ± 5.43, 186.09 ± 28.07, and 101.76 ± 22.48, respectively, P < 0.002). MMP-2 and TIMP-2 increased similarly in all infarcted groups. These findings suggest that the benefits of TNFR1 ablation might be attributable at least in part to the attenuation of cytokine-mediated imbalances in MMP-TIMP activity.
extracellular matrix; left ventricular function; myocardial infarction
Inflammatory cytokines such as tumor necrosis factor- (TNF-) are upregulated in myocardial injury states, including coronary micrombolization (9), ischemia-reperfusion, chronic ischemia post-MI, and heart failure (10, 23, 26). TNF- may contribute to myocardial injury because it has direct effects on myocardial contractile function by altering calcium homeostasis (12), excitation-contraction coupling (43), nitric oxide metabolism (3), and signaling through ceramide/sphingosine second messengers (38). In addition, TNF- may facilitate apoptosis (14). It is also involved in infiltration of neutrophils after ischemic injury. TNF- also contributes to ventricular remodeling (dilation and ECM turnover) associated with heart failure, mediated at least in part by TNF- activation of matrix metalloproteinases (MMPs). Indeed, mice overproducing TNF- in the myocardium display elevated activity of MMPs and cardiac dilation and develop a phenotype of overt heart failure (15).
The pathway of TNF--mediated changes in postinfarct remodeling is incompletely understood. Although it is known that TNF- acts through at least two different receptors [TNF- receptor 1 and 2 (TNFR1 and TNFR2)], it is not clear which receptor(s) mediates the effects of TNF- in the post-MI tissue processes of cardiac remodeling. Indeed, the effects of blocking TNF- in MI remain controversial; production of MI in mice lacking expression of both TNFR1 and TNFR2 led to increased infarct sizes and myocardial apoptosis in the early post-MI period (17), whereas pre-MI neutralization (22, 34) reduces infarct size. Furthermore, the reduction of ischemic injury achieved by late ischemia-reperfusion is dependent on TNF- (41), whereas the role of TNF- in the classical (early) preconditioning reduction of MI size remains unclear (4).
Therefore, in the present study, we used mice with a targeted deletion of TNFR1 to investigate the role of TNFR1 in both acute and chronic remodeling after MI. Survival, myocardial function, and MMP activity were assessed in both male and female mice.
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METHODS |
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MI was induced in four groups of mice: WT or TNFR1KO of both sexes. MI was induced by a modification of the method of Patten et al. (27). Briefly, mice were anesthetized with intraperitoneal ketamine (80 µg/g body wt) and xylazine (12 µg/g body wt), and the heart was approached via a left thoracotomy. The pericardium was stripped, and the left coronary artery was ligated at the tip of the left atrium. The infarction was made more extensive by gentle traction on the ligature to further expose the left coronary artery and placement of a second, more proximal ligature. By this method, we were able to increase the infarct size significantly, without any increase in immediate postoperative mortality (<24 h). Sham-operated animals had only the pericardium stripped; sham animals were analyzed 1 day and 6 wk postoperatively, after preliminary analysis showed a lack of significant difference between shams and controls in any of the measured parameters. MI mice were analyzed on days 1, 3, 7 (1 wk), and 42 (6 wk) after surgery. Control mice received no surgical intervention. Mice undergoing MI received analgesia with buprenorphine (0.05 mg/kg ip) given every 12 h for 48 h. Animals that died within 24 h of surgery (
3–5%) were excluded from the study because surgical error could not be excluded as the cause of these deaths.
Transesophageal echocardiography. Transesophageal echocardiography (TEE) was used in preference to traditional transthoracic echocardiography (TTE), because in a previous study (29) we demonstrated improved specificity and sensitivity with TEE compared with TTE when used in a murine MI model. Mice were anesthetized with 2.5% avertin (25 mg/ml 2,2,2 tribromoethanol and 2.5% tert-amyl alcohol in PBS, 18 µl/g body wt ip), and a 20-MHz intravascular ultrasound probe (Scimed; Maple Grove, MN) was introduced into the esophagus. Animals did not require ventilatory support for this procedure. Images were recorded on videotape and analyzed using an offline quantification system (ImageVue, Nova Microsonics; Allendale, NJ) for infarct size and LV dimensions and function. Images were recorded at the midpapillary level using a short-axis view of the LV. LV circumference was measured in systole (LVs) and diastole (LVd), and the values were used to calculate fractional area change (FAC) by the following formula: FAC (%) = [(LVd – LVs)/LVd] x 100. To assess infarct size, the infarcted segment was identified in the same view (akinetic in the initial stages, aneurismal in the later stages). The infarcted segment length was measured and divided by the diastolic circumference, and the result was expressed as a percentage. We measured each variable in triplicate and, based on our findings in the preliminary studies, used the maximum and minimum values for each variable for the above assessments.
In vivo hemodynamics. In the group of mice that was 42 days (6 wk) postinfarction, a 1.4-Fr conductance catheter (Millar Instruments; Houston, TX) was introduced into the LV via the right carotid artery as previously described (42). Continuous pressure-volume loops were recorded in the steady state, and data were analyzed (PVAN software, Millar Instruments) for LV ejection fraction, diastolic volume, and developed pressure (dP/dt). Calibration was performed as previously described (42). This procedure was performed immediately after TEE while mice were under continued anesthesia with 2.5% avertin.
Harvesting of samples.
After TEE (with or without conductance catheter measurement), mice were euthanized by cervical dislocation while under isoflurane anesthesia. Mice used for histological analysis were euthanized while under isoflurane anesthesia by lethal potassium chloride injection to minimize contraction necrosis. Hearts were washed in PBS, and the atria and right ventricle were removed before weighing. The LV was dissected under an operating microscope into infarct, peri-infarct, and remote zones. The infarct zone was identified visually by its apical orientation, pale color, and, in chronic cases, by profound ventricular wall thinning. Preliminary histology had identified the peri-infarct zone as an 1-mm section adjacent to the infarct zone, and this was therefore dissected using a 1-mm-thick rim. The remaining LV was treated as remote myocardium. Each zone was further divided into samples used for protein analysis and RNA extraction.
For protein extractions, tissue fragments were homogenized in a solution containing 0.05 M Tris·Cl (pH 7.5), 0.2% Brij 35, 0.075 M NaCl, and 1 µl/ml proteinase inhibitor (P8340, Sigma; St. Louis, MO) and centrifuged, and the supernatant was analyzed for total protein concentration by the method of Bradford. RNA extraction was done using RNeasy Mini Kits (Qiagen; Valencia, CA) as per the manufacturer's recommendation. DNAse I treatment (Ambion; Austin, TX) was performed off-column, because we observed improved 260-to-280-nm ratios by this method. The RNA yield was measured at 260 nm in triplicate. Finally, tissue from a subset of animals was used for immunohistochemical analysis (16).
Cardiac troponin I. In previous studies (29), we observed an excellent correlation between infarct size (as determined by histology) and serum cardiac troponin I (cTnI) obtained at 24 h postinfarction. Therefore, to ensure equivalence of myocardial injury between various groups, we measured cTnI in serum obtained from a subgroup of mice (n = 5 from each sex/genotype/surgery or control combination for a total of 12 groups) at 24 h postsurgery. Blood was obtained by tail clipping, and 50 µl of serum were used for cTNI ELISA (Bayer Diagnostics Advia Centaur Immunoassay System; Tarrytown, NY).
Measurement of MMP-2 and -9. MMP activity was measured using 100 µg protein/sample in chromogenic MMP-2 and -9 activity assays (Biotrak; Del Mar, CA), according to the manufacturer's protocol. These assays use a specific substrate for MMP-2 and -9, respectively. The samples were activated using p-aminophenylmercuricacetate according to the manufacturer's suggestion. Results obtained via spectrophotometry were compared against serial dilutions of known concentrations of the respective standards. Results were expressed in nanograms of MMP per 100 µg of protein.
Measurement of tissue inhibitors of MMPs, TNF-, IL-1
, and TNFR proteins.
Tissue inhibitor of MMP (TIMP)-1, TIMP-2, TNF-, IL-1, TNFR1, and TNFR2 protein levels were measured using ELISA kits (Amersham Biosciences; Piscataway, NJ; and R&D Systems; Minneapolis, MN), according to the manufacturer's instructions using 100 µg protein/sample. Results obtained via spectrophotometry were compared against serial dilutions of known concentrations of the respective standards.
Immunohistochemistry.
Four animals from each group (male MI WT, MI TNFR1KO, control WT, and control TNFR1KO) were processed for histology. Mouse hearts were fixed in 2% paraformaldehyde, cryopreserved in 30% sucrose, sectioned, and mounted as described (16). Sections were sequentially treated with PBS, blocking buffer (0.5% BSA and 0.15% glycine in PBS), and 5% normal goat serum (donkey serum for TIMP-1 slides) for 30 min. Immunofluorescent detection was performed using anti-TNF- (1:250, R&D Systems, cat. no. AF-410) and goat anti-rabbit IgG conjugated with CY3 (1:3,000, Jackson ImmunoResearch Laboratories; West Grove, PA). After treatment with secondary antibody, slides were sequentially rinsed with blocking buffer and PBS before nuclei were labeled with Hoechst 33342 (Sigma). Slides were viewed with an Olympus (Melville, NY) Provis AX70 fluorescent microscope at x40 magnification. Images were collected with a cooled charge-coupled device camera (Optronics Magnifier; East Muskogee, OK) at a 12-bit gray depth and assembled (Adobe Photoshop; San Jose, CA).
On the basis of preliminary experiments, the peri-infarct zone was identified as the site of greatest inflammatory cell density. This zone was found to consistently extend 1 mm from the infarct zone into the remote (uninfarcted) zone, with a clear demarcation identifying the infarcted area. Preliminary experiments also revealed that TNF--positive cells were present in the greatest concentration in this zone, with very few in the remote or infarct zones. To index the protein expression of TNF-, approximately five (2–5, mean 4.67) x40 images were taken of the peri-infarct zone from infarcted WT (n = 3) and TNFR1KO (n = 4) mice, counting 2,500–10,500 cells/mouse. A region of the LV free wall was analyzed in control (noninfarcted) mice (n = 4 for each genotype). Cells positive for TNF- were counted using an automated algorithm taking into consideration both pixel density as well as size of potential cells (Metamorph; Downingtown, PA). Data are expressed as means ± SD of TNF--positive cells per x40 field.
Real-time quantitative PCR.
mRNA transcripts for TNF-, IL-1, TIMP-1, TIMP-2, TIMP-3, TIMP-4, tissue-type plasminogen activator (t-PA), and urokinase-type plasminogen activator (u-PA) were quantified by real-time PCR. RNA (200 ng) was used to make cDNA as previously described (39). Primers were designed for real-time PCR using Primer Express software. The sequences and GenBank accession numbers are available on request. Primers were tested on cDNA, reverse transcriptase-negative samples, and 0.1% diethyl pyrocarbonate-treated water, and the amplification products electrophoresed on an agarose gel to assess the size of the product as well as to check for amplification of genomic DNA and primer-primer interactions. Equivalence and efficiency were tested by amplifications on serial dilutions of RNA (39). Real-time PCR was performed using an ABI 7700 (Applied Biosystems; Foster City CA) machine according to methods previously described (39). Threshold detection values were normalized to that of GAPDH.
Data analysis. Data are reported as means ± SD. ELISA results were expressed as absolute values of protein concentration, whereas real-time PCR data were expressed as fold upregulation compared with sex- and genotype-matched controls. Results of functional and biochemical tests were compared between groups for each time point by a nonparametric one-way ANOVA using the Kruskal-Wallis test. Upon detection of overall significance, limited hypothesis-driven post hoc analyses were performed using the Mann-Whitney U-test. Kaplan-Meier survival curves were generated, and differences in survival were assessed using the log-rank statistic (SPSS; Chicago, IL). A P value of <0.05 was considered significant.
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RESULTS |
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80% showed evidence of cardiac rupture (tear in peri-infarct myocardium and/or copious amount of clotted blood in the chest cavity >24 h postsurgery). No deaths were observed in any of the controls or shams (n = 5 for each sex and genotype).
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Cytokine expression.
Neither TNF- nor IL-1 proteins were consistently detectable by ELISA in any of the groups (MI, sham, and control) when using 100 µg protein/sample (data not shown). For this reason, we assessed these cytokines by real-time PCR and TNF- by immunohistochemistry. No difference was noted in TNF- mRNA between control animals of any sex and genotype combination. TNF- transcripts increased in a similar fashion in all four MI groups and in both remote and peri-infarct zones. In infarcted animals, there was a significant increase in the amount of TNF- mRNA relative to sex- and genotype-matched controls. Levels were highest in the periinfarct zone at day 1 (Fig. 5A) and day 3 (P < 0.02), whereas levels were near or at control levels by 1 wk. In the remote zone, levels peaked at days 3 and 7 (P < 0.04), but with more modest upregulation (Fig. 5B), and remained elevated at 42 days (P < 0.04). IL-1 mRNA was increased equally in all infarcted groups but had higher elevation compared with TNF-. The levels in the peri-infarct zone peaked at day 1 (P < 0.02), declined rapidly by day 3 (P < 0.02), but remained elevated out to 6 wk (P < 0.04) (Fig. 5C). The elevation in the remote zone was far more modest and peaked at 7 days (1 wk) postinfarct (P < 0.04; Fig. 5D). Levels for both TNF- and IL-1 transcripts rose slightly (but not reaching statistical significance) in sham animals at day 1 and fell to control values by day 3 (P = NS between shams and controls at any time point).
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rose similarly in all infarcted groups at day 3: 30 ± 3.2, 34 ± 6.8, 3.1 ± 1.4, and 3 ± 1.1 TNF--positive cells per x40 field in MI TNFR1KO males, MI WT males, TNFR1KO controls, and WT controls, respectively (P = NS between infarcted groups; P < 0.002 between all infarcted groups and controls).
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TNFR2 levels by ELISA were similar to controls in all infarcted animals at day 1 in both remote and periinfarct zones (data not shown). However, by day 3, the remote zone showed similar elevation in all groups (53 ± 14.7, 56 ± 9.3, 55 ± 11.4, 61 ± 11.9, 13 ± 2.5, and 17 ± 8.07 pg/100 µg protein, P = NS in MI TNFR1KO males, MI WT males, MI TNFR1KO females, MI WT females, TNFR1KO controls, and WT controls). The peri-infarct zone at day 3 showed a higher elevation that was again similar in all infarcted animals, irrespective of sex or TNFR1 status (120 ± 24, 113 ± 6.1, 106 ± 27.04, and 112 ± 10.8 pg/100 µg protein in MI TNFR1KO males, MI WT males, MI TNFR1KO females, and MI WT females, P = NS between groups, P < 0.004 vs. respective controls). Also of note, there were no sex differences of either TNFR1 or TNFR2 expression in control animals of any genotype.
MMP activity. Total MMP-9 activity increased in all the infarcted groups but was highest in MI WT males. In the peri-infarct zone (Fig. 7A), increased activity was seen as early as day 1 with levels peaking at day 3. The levels declined by day 7 but were still elevated in the MI WT females compared with MI TNFR1KO mice of both sexes (P < 0.04) at day 42.
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TIMPs. As seen in Fig. 8, the TIMP-1 mRNA level was markedly elevated in all MI groups compared with controls. However, MI WT males had significantly lower levels compared with all other groups. TIMP-1 protein, measured by ELISA, showed a similar, although not identical, pattern. Levels were lower in MI WT males (Fig. 8D) at day 3 in the remote zone. In the peri-infarct zone, MI WT males had lower levels of TIMP-1 protein at day 1, although this difference was resolved by day 3 (Fig. 8C).
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Plasminogen activators. t-PA mRNA levels as measured by real-time PCR showed a peak of 5- to 15-fold elevation in the peri-infarct zone at day 3 in all MI groups compared with controls. However, there was no difference in t-PA mRNA expression between the various MI groups in any of the zones. In all MI groups, u-PA also peaked at day 3 in the peri-infarct zone, with a 135- to 150-fold elevation in the peri-infarct zone and a 20- to 40-fold elevation in the remote zone compared with controls. No difference was seen between the various genotypes, or between males and females, in any of the zones.
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DISCUSSION |
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increases the expression and activity of some MMPs (such as the collagenases MMP-2 and MMP-9) as well as differentially alters the expression of TIMPs (20), allowing a shift toward greater proteolytic activity, collagen degradation, restructuring of the ECM (33), and progression of cardiac dilation (15, 33). In this study, we characterized the importance of TNFR1 in a murine model of MI by assessing survival, cardiac function, and remodeling in either WT mice or those having a deletion of the TNFR1 gene (TNFR1KO), studying both male and female mice at different intervals after the induction of MI. This investigation yielded three principal findings: 1) MI WT female mice had a better survival than MI WT male mice; however, ablation of TNFR1 substantially improved survival after MI in both sexes; 2), MI TNFR1KO mice showed significantly less cardiac hypertrophy and dilation and better preservation of systolic function relative to MI WT mice; these effects were more notable in male mice relative to female mice; and 3) TNFR1 ablation improved the MMP-9/TIMP-1 balance, an important mediator of ECM remodeling. In contrast, ablation of TNFR1 did not influence MI-induced changes in the expression or activity of other proteins important to remodeling of the myocardium, including TNF-, IL-1, TNFR2, TIMP-2, TIMP-3, TIMP-4, u-PA, t-PA, and MMP-2.
In the present study, early (<1 wk) post-MI death showed a marked difference according to sex. Although not all mice that died early were available for postmortem examination, of those examined, most had signs of cardiac rupture. Relative to female mice, an increased prevalence (30%) of early death from cardiac rupture in post-MI male mice has been previously observed (11). The greater incidence of early death in male MI WT mice in this study (95%) may arise from a larger area of infarction [48% in this report vs. 38.6% (11)]. However, both acute rupture and more delayed alterations in cardiac remodeling (dilation, hypertrophy, and systolic function) appear related to processes associated with remodeling of the ECM (11). It is striking that in the post-MI period, WT male mice show markedly lower levels of TIMP-1 expression and higher levels of MMP-9 activity relative to WT female mice, which displayed better post-MI survival and less cardiac remodeling. However, compared with MI TNFR1KO animals of either sex, MI WT females had poorer survival and function and had correspondingly higher MMP-9 at 1 and 42 days and lower TIMP-1 at 3 and 7 days.
Such results are congruent with prior observations showing that 1) WT male mice are more likely to die acutely from cardiac rupture after MI relative to WT females (11), 2) mice with TIMP-1 gene ablation demonstrated greater chamber dilation and loss of systolic function after MI (11), and 3) transient overexpression of TIMP-1 after MI significantly blunted the frequency of cardiac rupture (11). The present observations suggest that in male mice, a TNFR1-mediated process limits the production of TIMP-1, with such inhibition removed by TNFR1 gene ablation. However, this does not appear to occur through sex-related differences in the level of TNFR1 or TNFR2 protein (as detected by ELISA) in cardiac homogenates. Thus at least in the strain of mice used in this study (C57/BL6J), the sex-related differences in cardiac TNFR1 and TNFR2 transcripts observed in FVB/NJ (Jackson Laboratories, catalog no. 1800) mice (13) are not reflected in sex-dependent differences in TNFR1 and TNFR2 proteins.
However, the sex-related differences observed in this study might be related to the location of the TIMP-1 gene on the X chromosome (1). Normally, one copy of X chromosome genes is inactivated to ensure dosage compensation between males and females. However, in the case of many genes, including TIMP-1, RNA expression has been demonstrated from the inactive X chromosome (2). Indeed, in some cell lines, a biallelic level of expression has been shown, possibly related to the methylation state of the TIMP-1 promoter region in the inactive X chromosome (2). Thus WT females might mount a more vigorous TIMP-1 response, with the ensuing elevation of TIMP-1 expression limiting cardiac rupture and remodeling through decreased MMP activity and degradation of the ECM, particularly in the peri-infarct zone, which is susceptible to rupture (11). In addition, TIMP-1 has been studied for its growth-promoting potential separate from MMP inhibition activity (8). Thus elevated TIMP-1 expression could enhance the wound-healing process of the infarct and peri-infarct zones.
Ablation of TNFR1 expression not only abolished sex-related differences in survival after MI but also improved matrix homeostasis and LV performance irrespective of sex. In a variety of cell types, TNF- induces MMP-9 expression, possibly via AP-1 and NF-
B transcriptional regulatory elements in the MMP-9 promoter (5). In the present study, MMP-9 levels were higher in WT animals at all time points, suggesting that the TNFR1 is a primary mediator for MMP-9 induction and that this induction persists far longer than the upregulation of TNF-. In this study, MMP-9 also showed a sex-based difference in response to MI. Sex steroid regulation of MMP expression/activity has been previously suggested because the levels of breast tumor MMP-9 and TIMP-1 vary with phases of the menstrual cycle (31). Conversely, rat prostate glands showed increased MMP activity after long-term exposure to androgen and estrogen (19).
The present study investigated long-term post-MI outcomes in cardiac function and remodeling as a consequence of ablation of TNFR1-dependent signaling, particularly with respect to important mediators of cardiac remodeling (TIMPs and MMPs). Previous studies have investigated the short-term effects (3 h to 2 days post-MI) of inhibition of TNF- signaling in rodents subjected to MI. Whereas ablation of either the TNFR1 or TNFR2 gene did not alter infarct size in mice at 1 day post-MI, ablation of both TNFR1 and TNFR2 genes increased infarct size (at 24 h post-MI) and frequency of acute (3 h post-MI) apoptosis (17). Thus the reduction of acute apoptosis through TNF signaling may reduce infarct size. Conversely, local overexpression of a TNF-neutralizing protein (soluble TNFR1) in the male rat myocardium subjected to MI led to decreased size of MI and decreased (but not normalized) levels of bioactive TNF-, caspase activity, and apoptosis when analyzed at 2 days post-MI (36). In this case, it is feasible that a low level of TNF- signaling persisted or that soluble TNFR1 changed the ratio of bioactive soluble TNF- (17 kDa) and membrane-bound TNF- (26 kDa) as well as the balance of signaling through TNFR1 or TNFR2 pathways, which show differential affinity for these two forms of TNF- (21). This may prove important in resolving the disparate results in these acute post-MI studies because either TNF receptor may be involved in survival or apoptosis signaling pathways in various cell types (21).
In the present study, cardiac TNF- RNA expression was early and transient (maximum induction at approximately days 1–3 post-MI), whereas TNF- protein was not detectable by ELISA with an estimated sensitivity of <6 pg/mg cardiac protein at any time point. However, confirmation of TNF- protein expression was obtained by immunohistochemical detection of cells producing TNF-, which was similarly elevated in both MI WT and MI TNFR1KO mice relative to WT or TNFR1KO controls. Nevertheless, this relatively low level of TNF- expression appears to significantly disrupt matrix equilibrium and does so long after the TNF- rise has subsided. However, important responses to transient, low levels of TNF- expression are not without precedent. Hemorrhagic shock (HS) induces a very modest (2-fold) and transient (1 h post-HS) increase in pulmonary TNF- expression that is required to produce, through TNFR1-mediated pathways, a delayed (4 h post-HS) pulmonary neutrophil infiltration (35). Thus it is possible that in the early stages postinfarction, the role of TNF- is to promote neutrophil infiltration and release of MMP-9, initiating an MMP-9/TIMP-1 imbalance and the commencement of LV dilatation.
In summary, the relative preservation of matrix homeostasis in mice lacking TNFR1 expression suggests that, although other factors may play a role in matrix disequillibrium, TNFR1-dependent signaling is an important regulator of the MMP/TIMP balance and subsequent cardiac remodeling in the postinfarction myocardium.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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M. Wang, T. Markel, P. Crisostomo, C. Herring, K. K. Meldrum, K. D. Lillemoe, and D. R. Meldrum Deficiency of TNFR1 protects myocardium through SOCS3 and IL-6 but not p38 MAPK or IL-1beta Am J Physiol Heart Circ Physiol, April 1, 2007; 292(4): H1694 - H1699. [Abstract] [Full Text] [PDF]
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P < 0.003, WT females vs. TNFR1KO females.
WT males vs. WT females; 
WT females vs. all TNFR1KO (males + females). n = 5 for each genotype, sex, and time point except for MI-WT males at 6 wk, where n = 0.
