Palmitate-Induced MMP-9 Expression in the Human Monocytic Cells is Mediated through the TLR4-MyD88 Dependent Mechanism

Abstract

Background/Aims: Obese individuals are known to have increased Matrix metalloproteinase (MMP)-9 plasma levels and MMP-9 is reported to play an important role in obesity-associated adipose tissue inflammation. Since in obesity, the levels of circulatory saturated free fatty acid (FFA) palmitate (palimitic acid) are increased and modulate the expression of inflammatory mediators, the role of palmitate in the regulation of MMP-9 remains unclear. Methods: Human monocytic cell line THP-1 and primary monocytes were stimulated with palmitate and TNF-α (positive control). MMP-9 expression was assessed with real time RT-PCR and ELISA. Signaling pathways were studied by using THP-1-XBlue™ cells, THP-1-XBlue™-defMyD cells, anti-TLR4 mAb and TLR4 siRNA. Phosphorylation of NF-kB and c-Jun was analyzed by Western blotting. Results: Here, we provide the evidence that palmitate induces MMP-9 expression at both mRNA (THP-1: 6.8 ± 1.2 Fold; P = 0.01; Primary monocytes: 5.9 ± 0.7 Fold; P = 0.0003) and protein (THP1: 1116 ±14 pg/ml; P<0.001; Primary monocytes: 1426 ± 13.8; P = 0.0005) levels in human monocytic cells. Palmitate-induced MMP-9 secretion was markedly suppressed by neutralizing anti-TLR-4 antibody (P < 0.05). Furthermore, genetic silencing of TLR4 by siRNA also significantly abrogated the palmitate-induced up-regulation of MMP-9. Additionally, MyD88^-/- THP-1 cells did not express MMP-9 in response to palmitate treatment. Increased NF-κB/AP-1 activity (P<0.05) was also observed in palmitate-treated THP-1 cells. Conclusion: Altogether, these results show that palmitate induces TLR4-dependent activation of MMP-9 gene expression, which requires the recruitment of MyD88 leading to activation of NF-kB/AP-1 transcription factors. Thus, our findings suggest that the palmitate-induced MMP-9 secretion might be an underlying mechanism of its increased levels in obesity and related metabolic inflammation.

Pam3CSK4 Induces MMP-9 Expression in Human Monocytic THP-1 Cells

“…In obesity, MMP-9 may facilitate the infiltration of immune cells into the adipose tissue and could promote obesity-associated metabolic inflammation. We earlier showed that microbial components and the free fatty acid palmitate induced robust MMP-9 production in monocytic cells [19,24]. Bacterial lipoprotein were shown to induce inflammatory mediators including IL-6, TNF-α, IL-8, CSF2, CSF3, and ICAM1and IL-1β [32].…”

“…The interaction of different ligands with the TLRs has been shown to be involved in MMP-9 production. The free fatty acid palmitate is considered as an endogenous ligand for TLR4 and it induces TLR4-dependent activation of MMP-9 gene expression which requires MyD88 recruitment and activation of NF-κB/AP-1 transcription factor [19]. Likewise, a microbial component FSL-1 was also shown to trigger MMP-9 production in a TLR-2-dependent manner though the recruitment of MyD88 and…”

Palmitate Activates CCL4 Expression in Human Monocytic Cells via TLR4/MyD88 Dependent Activation of NF-κB/MAPK/ PI3K Signaling Systems

“…Several reports showed a possible mechanistic link between FFAs and innate immune toll-like receptors (TLRs) in metabolic disease. TLRs are a family of pattern recognition receptors that activate the innate immune responses upon interaction with various pathogen-associated molecular patterns, including lipids, lipoproteins, proteins and FFAs [10-12]. After ligand binding, TLRs engage Toll/Interleukin-1 receptor (TIR) domain-containing adaptor proteins (either myeloid differentiation primary-response protein 88 (MyD88) and MyD88-adaptor-like protein (MAL), or TIR domain-containing adaptor protein inducing IFNβ (TRIF) and TRIF-related adaptor molecule (TRAM).…”

“…After ligand binding, TLRs engage Toll/Interleukin-1 receptor (TIR) domain-containing adaptor proteins (either myeloid differentiation primary-response protein 88 (MyD88) and MyD88-adaptor-like protein (MAL), or TIR domain-containing adaptor protein inducing IFNβ (TRIF) and TRIF-related adaptor molecule (TRAM). This association triggers the recruitment and activation of IRAK1, forming a complex with TRAF6 and activating transcription factors including NF-kB and AP-1[10, 13-15] . FFAs induce inflammatory mediators’ production in immune cells via TLR-4.…”

Angiotensin II Suppresses Rev-erbα Expression in THP-1 Macrophages via the Ang II Type 1 Receptor/Liver X Receptor α Pathway

“…In addition, excessive levels of angiotensin II (Ang II), the major stress hormone in the rennin-angiotensin system (RAS), have been confirmed to accelerate the progression of atherosclerotic plaques toward instability via MMPs induction [11, 12]. These actions are mainly mediated through Ang II type 1 receptor (AT1R) [11, 13, 14] and its downstream signaling molecules, including nuclear factor-kappa B (NF-κB), liver X receptor α (LXRα), Toll-like receptors (TLRs) and peroxisome proliferators–activated receptor γ (PPARγ) [15-17]. Interestingly, Ang II also regulates the mRNA expression of some core clock and clock related genes, such as Period, Dbp, Bmal1, and Rev-erbα, in cultured vascular smooth muscle cells and hearts of rats [18, 19].…”