Regulation of Macrophage-Derived Fibroblast Growth Factor Release by Arachidonate Metabolites

Abstract

The macrophage is a source of many mediators with direct and indirect fibrogenic potential. In this study, release of macrophage-derived fibroblast growth factor (MDGF) activity by murine peritoneal macrophages is examined with regard to its regulation by arachidonate metabolites. Upon stimulation with 10 micrograms/ml lipopolysaccharide (LPS), resident peritoneal macrophages from CBA/J mice released MDGF activity into media rapidly, reaching maximal levels in approximately 1 h. Lysates of these stimulated cells also revealed significantly increased cell-associated MDGF activity, composing 45% of the total assayable activity. This activity, as assayed by radioactive thymidine incorporation by primary cultures of rat lung fibroblasts, was separable from interleukin-1 (IL-1) activity by reverse phase high performance liquid chromatography (HPLC). Furthermore, purified murine IL-1 had no MDGF activity in this assay system. This stimulated MDGF release was enhanced by the cyclooxygenase inhibitors indomethacin, ibuprofen, and aspirin at micromolar concentrations, but inhibited in a dose-dependent manner by prostaglandin E2 (PGE2). On the other hand, nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor was inhibitory at 0.1 and 0.4 microM but not at 2.5 microM. Zymosan-stimulated macrophages also markedly increased MDGF release, albeit with a different time course which was characterized by a delay of approximately 7 h before peak levels were attained. Such stimulation, which is known to cause increased lipoxygenase activity, was also inhibited by 0.5 microM NDGA. In contrast, the lipoxygenase pathway products leukotrienes B4 (LTB4) and C4 (LTC4) stimulated MDGF release in a dose-dependent (10(-10)-10(-8) M) manner, with LTC4 being more potent on a per unit dose basis. Stimulation by LTC4 was inhibited by the putative leukotriene receptor antagonist, FPL55712, while LTD4 and LTE4 did not stimulate MDGF release, thus suggesting the mediation of this effect by specific LTC4 receptors. These data suggest also that products of the cyclooxygenase and lipoxygenase pathways are potentially important both as exogenous (ie, derived from cells other than the macrophage itself) and auto- or self-regulators of macrophage MDGF release. This, in turn, implies that cyclooxygenase products are antifibrogenic and important in maintaining or returning to the quiescent or normal state, whereas the lipoxygenase products are profibrogenic and important in induction of fibrosis or wound-healing and tissue repair. Any alteration in the balance between these two pathways may result in either a desirable or a harmful outcome.

The role of leukotrienes in airway inflammation

“…Recent evidence suggests that cysLTs have a key regulatory role in remodeling, the structural changes of the airway that are nearly universally seen in asthma. 52,57,75 CysLTs promote collagen synthesis and release by mitogen-stimulated lung fibroblasts. 52 Moreover, LTs appear to be essential for pulmonary fibrosis to develop, suggesting a role of LTs in fibroproliferative processes, such as airway wall remodeling.…”

Leukotriene B4 at low dosage negates the catabolic effect of prostaglandin E2 in human patellar tendon fibroblasts

“…On the other hand, LTB 4 at picomolar concentrations has been shown to stimulate DNA synthesis in cultured human epidermal keratinocytes and to induce proliferation of arterial smooth muscle cells in primary culture (Kragballe et al, 1985;Palmberg et al, 1989). Also, leukotrienes at low concentrations (0.1 to 1 nM) stimulate collagen synthesis of lung fibroblasts (Phan et al, 1987(Phan et al, , 1988. Thus, although LTB 4 has been implicated in the pathogenesis of various inflammatory diseases (Davidson et al, 1983;Sharon and Stenson, 1984;Konstan et al, 1993), its potential role in the tendon tissue homeostasis as well as pathogenesis remains to be explored.…”

Minerals, Fibrosis, and the Lung

“…Modulation ofMDGF release from murine peritoneal macrophages may be effected by arachidonic acid metabolites, cyclooxygenase products being antifibrogenic and lipoxygenase products being proliferative (240). Disturbance ofthe equilibrium between these opposing actions seems likely to determine whether fibrosis proceeds or recedes, in combination with control of endogenous fibroblast PGE2 production.…”