Nickel and the Microbial Toxin, MALP-2, Stimulate Proangiogenic Mediators from Human Lung Fibroblasts via a HIF-1α and COX-2–Mediated Pathway

Abstract

Hypoxia-inducible factor (HIF-1alpha) and cyclooxygenase-2 (COX-2) have been implicated in the regulation of inflammatory-like processes that lead to angiogenesis and fibrotic disorders. Here we demonstrate that in human lung fibroblasts (HLFs) treated with mixed exposures to chemical and microbial stimuli, HIF-1alpha stabilization plays a pivotal role in the induction of COX-2 mRNA and protein, driving the release of vascular endothelial growth factor (VEGF) and proangiogenic and profibrotic chemokines. Upon costimulation with Ni and the mycoplasma-derived lipopeptide macrophage-activating lipopeptide-2 (MALP-2), there was a synergistic induction of CXCL1 and CXCL5 mRNA and protein release from HLF, as well as an enhanced response in VEGF compared to either stimulus alone. Consistent with our previous findings that Ni and MALP-2 stimulates the induction of CXCL8 via a COX-2-mediated pathway, CXCL1, CXCL5, and VEGF release were also regulated by COX-2. Ni induced the stabilization of HIF-1alpha protein in HLF, which was further enhanced in the presence of MALP-2. Depletion of HIF-1alpha using siRNA blocked COX-2 induction by Ni and MALP-2 along with the release of VEGF, CXCL1, CXCL5, and CXCL8. Our results indicate that Ni and MALP-2 interact to promote an angiogenic profibrotic phenotype in HLF. Moreover, these findings reveal a potential role for HIF-1alpha in mediating chemical-induced alterations in cellular response to microbial stimuli, modulating pulmonary inflammation and its consequences such as fibrosis and angiogenesis.

Multiple protein kinase pathways mediate amplified IL-6 release by human lung fibroblasts co-exposed to nickel and TLR-2 agonist, MALP-2

“…In our previous studies dissecting the signaling mechanisms responsible for Ni and MALP-2 synergistic amplification of CXC chemokines, such as IL-8/CXCL8, we observed fundamental roles for hypoxia-inducible factor 1α (HIF-1α) and cyclooxygenase 2 (COX-2) in mediating IL-8 release from HLF (Brant and Fabisiak, 2008; Brant and Fabisiak, 2009). It was important, therefore, to determine if Ni and MALP-2 interact via similar mechanisms to direct IL-6 release.…”

“…Macrophage activating lipopeptide-2 (MALP-2), a Toll-like receptor-2 (TLR-2) agonist derived from Mycoplasma fermentans , could recapitulate the effects of live infection suggesting an interaction (or a “cross-talk”) between TLR-2-dependent and Ni-dependent signaling processes. The specific mechanisms responsible for this interaction on IL-6 remain to be identified, although synergistic interactions between Ni and MALP-2 on release of IL-8 utilized hypoxia inducible factor 1α (HIF-1α)- and cyclooxygenase 2 (COX-2)-dependent signaling pathways (Brant and Fabisiak, 2008; Brant and Fabisiak, 2009). …”

Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus Induces Prostaglandin E 2 Production through Cyclooxygenase 1, Which Is Dependent on the ERK1/2-p-C/EBP-β Pathway

“…COX is the rate-limiting enzyme in the PGE 2 synthesis cascade. COX-2 is normally absent from cells, and when induced, the COX-2 protein level increases on a scale of hours after a single stimulus (35). COX-1, on the other hand, is often referred to as a housekeeping enzyme because it is constitutively expressed in almost all tissues and performs an important function in mediating various normal physiological processes (29,36).…”

Mycoplasma fermentans MALP-2 Induces Heme Oxygenase-1 Expression via Mitogen-Activated Protein Kinases and Nrf2 Pathways To Modulate Cyclooxygenase 2 Expression in Human Monocytes

“…In human placental trophoblast cells, the expression of COX-2 and production of PGE 2 caused by MALP-2 may be involved in the mechanism of preterm labor (30). COX-2-mediated pathways were involved in the production of CXC motif chemokine ligand 8 (CXCL8), CXCL1, CXCL5, and vascular endothelial growth factor (VEGF), which may have important roles in the pathogenesis of pulmonary fibrotic disorders (42). Therefore, elucidating the mechanism by which COX-2 expression is regulated will be crucial to our understanding of these COX2-regulated pathophysiological processes.…”