ASK1-p38 MAPK-p47phox activation is essential for inflammatory responses during tuberculosis via TLR2-ROS signalling

Abstract

SummaryThe roles of intracellular reactive oxygen species (ROS) and related signalling pathways in mycobacterial infection are largely unknown. Here we show that tuberculin purified protein derivative (PPD)/Toll-like receptor (TLR) 2/ROS signalling through activation of apoptosis-regulating signal kinase (ASK) 1 and p47phox pathways is responsible for the induction of proinflammatory responses during tuberculosis (TB) infection. Tuberculin PPD stimulation resulted in rapid activation of mitogen-activated protein kinases (MAPKs) and an early burst of ROS in monocytes/ macrophages in a TLR2-dependent manner. PPDinduced ROS production led to robust activation of ASK1 upstream of p38 MAPK, via TLR2. Interestingly, phosphorylation of the cytosolic NADPH oxidase subunit p47phox and ASK1 activation are mutually dependent on PPD/TLR2-mediated signalling. Furthermore, active pulmonary TB patients showed upregulated ROS generation, as well as enhanced activation of ASK1/p38/p47phox pathways in their primary monocytes compared with healthy controls, which suggests a systemic primed status during TB. Taken together, these results indicate that activation of the ASK1/p38 MAPK/p47phox cascade plays a central role in PPD/TLR2-induced ROS generation and suggests the existence of a 'ROS/ASK1' inflammatory amplification feedback loop in monocytes/ macrophages. The altered regulation of this axis with an increasing free-radical burden may contribute to the immunopathogenesis of human TB.

NADPH Oxidase 2 Interaction with TLR2 Is Required for Efficient Innate Immune Responses to Mycobacteria via Cathelicidin Expression

“…These data concur with our previous findings that tuberculin PPD-induced ROS production is dependent on TLR2 in monocytes/macrophages (13). In addition, our study shows that Mtb treatment triggered biphasic association of TLR2 and NOX2 at 1 min and 30 min (see Fig.…”

“…Previously, we showed that a tuberculin PPD could inhibit the activation of inflammatory signaling by TLR2 in murine BMDMs and human primary monocytes (13). In the current study, we extended this observation to demonstrate that Mtb-mediated ROS production is largely dependent on NOX2 and TLR2.…”

“…Previous studies revealed that TLR4/LPS stimulation induced the production of intracellular ROS, which are required for the formation of a complex between the adaptor molecule TNFR-associated factor (TRAF) 6 and apoptosis signal-regulating kinase 1 and the subsequent activation of innate immune responses (12). We also recently showed that the mycobacterial tuberculin purified protein derivative (PPD) activates TLR2-dependent proinflammatory signaling in monocytes/macrophages via intracellular ROS (13). Furthermore, the direct interaction of TLR4 with NOX4, a protein related to NOX2, is involved in TLR4-mediated ROS production and NF-B activation (14).…”

Antioxidant Defenses of Francisella tularensis Modulate Macrophage Function and Production of Proinflammatory Cytokines

“…This results in the phosphorylation and activation of downstream p38 and JNK (49). We determined the activation state of ASK1 by Western blotting analysis.…”

FcγR-driven Release of IL-6 by Macrophages Requires NOX2-dependent Production of Reactive Oxygen Species

“…One major source of ROS in macrophages is the phagocytic NADPH oxidase complex (NOX2), which consists of a membrane-bound fraction (gp91 phox and p22 phox ) and an array of cytoplasmic factors (p40 phox , p47 phox , p67 phox , and Rac) that translocate to the membrane resulting in formation of a primed and active NOX2 complex (4 -7). ROS production occurs following Fc␥R cross linking (8,9), during phagocytosis (2,10), and engagement of TLR4 or TLR2 (11)(12)(13). Superoxide radicals (O 2 . )…”