Pressure overload-dependent membrane type 1-matrix metalloproteinase induction: relationship to LV remodeling and fibrosis.

Increased myocardial extracellular matrix collagen represents an important structural milestone during the development of left ventricular (LV) pressure overload (PO); however, the proteolytic pathways that contribute to this process are not fully understood. This study tested the hypothesis that membrane type 1-matrix metalloproteinase (MT1-MMP) is directly induced at the transcriptional level in vivo during PO and is related to changes in LV collagen content. PO was induced in vivo by transverse aortic constriction in transgenic mice containing the full length human MT1-MMP promoter region ligated to luciferase (MT1-MMP Prom mice). MT1-MMP promoter activation (luciferase expression), expression, and activity; collagen volume fraction (CVF); and left atrial dimension were measured at 1 (n = 8), 2 (n = 12), and 4 (n = 17) wk following PO. Non-PO mice (n = 10) served as controls. Luciferase expression increased by fivefold at 1 wk, fell at 2 wk, and increased again by ninefold at 4 wk of PO (P < 0.05). MT1-MMP expression and activity increased at 1 wk, fell at 2 wk, and increased again at 4 wk after PO. CVF increased at 1 wk, remained unchanged at 2 wk, and increased by threefold at 4 wk of PO (P < 0.05). There was a strong positive correlation between CVF and MT1-MMP activity (r = 0.80, P < 0.05). Left atrial dimension remained unchanged at 1 and 2 wk but increased by 25% at 4 wk of PO. When a mechanical load was applied in vitro to LV papillary muscles isolated from MT1-MMP Prom mice, increased load caused MT1-MMP promoter activation to increase by twofold and MT1-MMP expression to increase by fivefold (P < 0.05). These findings challenge the canonical belief that PO suppresses overall matrix proteolytic activity, but rather supports the concept that certain proteases, such as MT1-MMP, play a pivotal role in PO-induced matrix remodeling and fibrosis.

IL-12 stimulates the osteoclast inhibitory peptide-1 (OIP-1/hSca) gene expression in CD4+ T cells.

Immune cell products such as interferon (IFN)-gamma and interleukin (IL)-12 are potent inhibitors of osteoclast formation. We previously characterized the human osteoclast inhibitory peptide-1 (OIP-1/hSca), a Ly-6 gene family member and showed IFN-gamma modulation of OIP-1 expression in bone marrow cells. Whether, IL-12 regulates OIP-1 expression in the bone microenvironment is unclear. Real-time PCR analysis revealed that IL-12 treatment significantly enhanced OIP-1 mRNA expression in human bone marrow mononuclear cells. Because IL-12 induces IFN-gamma production by T cells, we tested whether IFN-gamma participates in IL-12 stimulation of OIP-1 gene expression in these cells. IL-12 treatment in the presence of IFN-gamma neutralizing antibody significantly increased OIP-1 mRNA expression, suggesting that IL-12 directly regulates OIP-1 gene expression. Interestingly, real-time PCR analysis demonstrated that IL-12 induces OIP-1 expression (3.2-fold) in CD4+ T cells; however, there was no significant change in CD8+ T cells. Also, IL-12 (10 ng/ml) treatment of Jurkat cells transfected with OIP-1 gene (-1 to -1,988 bp) promoter-luciferase reporter plasmid demonstrated a 5-fold and 2.7-fold increase in OIP-1 gene promoter activity in the presence and absence of antibody against IFN-gamma, respectively. We showed that STAT-1,3 inhibitors treatment significantly decreased IL-12 stimulated OIP-1 promoter activity. Chromatin immunoprecipitation (ChIP) assay confirmed STAT-3, but not STAT-1 binding to the OIP-1 gene promoter in response to IL-12 stimulation. These results suggest that IL-12 stimulates the OIP-1 gene expression through STAT-3 activation in CD4+ T cells.

Aortic dilatation with bicuspid aortic valves: cusp fusion correlates to matrix metalloproteinases and inhibitors.

BACKGROUND: Congenital bicuspid aortic valves (BAVs) result from fusion of 2 valve cusps, resulting in left-noncoronary (L-N), right-left (R-L), and right-noncoronary (R-N) morphologic presentations. BAVs predispose to ascending thoracic aortic aneurysms (ATAAs). This study hypothesized that ATAAs with each BAV morphologic group possess unique signatures of matrix metalloproteinases (MMPs) and endogenous tissue inhibitors of metalloproteinases (TIMPs). METHODS: Ascending thoracic aortic aneurysm tissue from 46 patients with BAVs was examined for MMP/TIMP abundance, and global MMP activity was compared with normal aortic specimens (n=15). Proteolytic balance was calculated as the ratio of MMP abundance to a composite TIMP score. Results were stratified by valve morphologic group (L-N [n=6], R-L [n=31], and R-N [n=9]). RESULTS: The BAV specimens (p<0.05 versus normal aorta, 100%) displayed elevated global MMP activity (273%±63%), MMP-9 (263%±47%), and decreased MMP-7 (56%±10%), MMP-8 (58%±11%), TIMP-1 (63%±7%), and TIMP-4 (38%±3%). The R-L group showed increased global MMP activity (286%±89%) and MMP-9 (267%±55%) with reduced MMP-7 (45%±7%), MMP-8 (68%±15%), TIMP-1 (58%±7%), and TIMP-4 (35%±3%). The L-N group showed elevated global MMP activity (284%±71%) and decreased MMP-8 (37%±17%) and TIMP-4 (48%±14) activity. In the R-N group, MMP-7 (46%±13%) and MMP-8 (36%±17%) and TIMP-1 (59%±10%) and TIMP-4 (42%±5%) were decreased. The R-L group demonstrated an increased proteolytic balance for MMP-1, MMP-9, and MMP-12 relative to L-N and R-N. CONCLUSIONS: Each BAV morphologic group possesses a unique signature of MMPs and TIMPs. MMP/TIMP score ratios suggest that the R-L group may be more aggressive, justifying earlier surgical intervention.

Relationship between the temporal profile of plasma microRNA and left ventricular remodeling in patients after myocardial infarction.

BACKGROUND: microRNAs (miRs) are small noncoding RNAs that recognize and bind to mRNAs and inhibit protein translation or degrade mRNA. Studies in animal models have suggested that miRs play a translational or posttranslational regulatory role in myocardial growth, fibrosis, viability, and remodeling. However, whether specific temporal changes in miRs occur in patients during the left ventricular (LV) remodeling process that follows a myocardial infarction (post-MI) remains unknown. The current pilot study tested the hypotheses that plasma miRs could be reliably measured in post-MI patients and that there is a relationship between temporal changes in specific miRs and post-MI LV structural remodeling. METHODS AND RESULTS: LV end-diastolic volume (echocardiography) and plasma miR were measured in age-matched referent controls (CTLs, n=12) and post-MI patients (n=12) from day 2 through day 90 post-MI. Selected miRs (miR-1, miR-21, miR-29a, miR-133a, and miR-208) were measured using quantitative reverse transcription-polymerase chain reaction and normalized for endogenous small nuclear RNA U6. After MI, LV end-diastolic volume increased progressively compared with CTL; this was accompanied by time-dependent changes in specific miRs. For example, miR-21 initially decreased 2 days post-MI (0.3 ± 0.1-fold versus CTL; P<0.05), increased 5 days post-MI (2 ± 1-fold versus CTL; P<0.05), and returned to CTL values at later post-MI time points. In contrast, miR-29a increased 5 days post-MI (4 ± 1-fold versus CTL; P<0.05) and then decreased to CTL at later time points. miR-208 increased 5 days post-MI (3 ± 1-fold versus CTL; P<0.05) and remained elevated up to 90 days post-MI. CONCLUSIONS: A time-dependent change in miRs occurred in post-MI patients, including an early and robust increase in miRs that has affected myocardial growth, fibrosis, and viability. Thus, serially profiling miRs in the plasma of post-MI patients may hold both mechanistic and prognostic significance.