Lipoteichoic acid modulates inflammatory response in macrophages after phagocytosis of titanium particles through Toll‐like receptor 2 cascade and inflammasomes

Abstract

Toll-like receptor 2 (TLR2) and nucleotide-binding and oligomerization domain-like receptors with a pyrin domain 3 (NLRP3) inflammasomes have been presumed to participate in the pathogenesis of aseptic implant loosening. The aim of this study is to analyze the cellular localization of TLR2 and NLRP3 inflammasomes in the periprosthetic tissue from aseptically loose hip implants as well as the expression of these molecules in macrophages stimulated in vitro with titanium particles (Ti) coated with lipoteichoic acid (LTA). Using immunohistochemistry, immunoreactivity of TLR2 and NLRP3 inflammasomes was found in macrophages within the foreign body granulomatosis. Using RAW264.7 cells, stimulation with Ti increased the messenger RNA (mRNA) levels of TLR2 and TNF-α. Stimulation with LTA-coated Ti enhanced mRNA levels of NLRP3 and IL-1β, whereas reinforced secretion of IL-1β was not detected in spite of marked release of TNF-α. Finally, the same cells with silenced Irak2, an adaptor protein in the TLR2 cascade, suppressed this NLRP3 upregulation. This study suggests that TLR2 and NLRP3 inflammasomes are factors involved in cross-talk mediating the foreign body type response to wear particles. In addition, discrepant behavior in the release between TNF-α and IL-1β release may explain the variable pathomechanisms of aseptic implant loosening without acute inflammatory reactions.

Inflammatory osteolysis: a conspiracy against bone

“…On the other hand, prosthetic particles generate priming signals through TLRs that induce expression of pro-IL-1β and NLRP3 (145,146). The NLRP3 inflammasome, however, appears to supersede TLR4 signaling in prosthetic-wear particle-induced osteolysis (147).…”

TLR4 (not TLR2) dominate cognate TLR activity associated with CoCrMo implant particles

“…23 Previous investigations indicate that mRNA expression of TLR2 and TLR4 are inversely related, depend- ing on the specific PAMP agonist present with Tiparticles. [24][25][26] LPS-coated titanium particles, have been shown to decrease macrophage mRNA expression of TLR4 but not in response to LPS-free Ti particles, which had the opposite effect, increasing TLR4 mRNA expression up to 12 h after challenge. 24 This is consistent with the current investigation, which demonstrated increases in TLR4 cell surface expression to CoCrMo particle challenge.…”

“…Conversely, mRNA of TLR2 has been shown to be up‐regulated in response to Ti/LPS+ . Another recent investigation showing different responses of TLR2 and TLR4 that also used Ti particles but with the TLR2 PAMP LTA, demonstrated a marked decrease of TLR2 but an increase of TLR4 mRNA expression …”

Review: the potential impact of surface crystalline states of titanium for biomedical applications

“…As a result of NF-κB activation, macrophages start to secrete a panel of pro-inflammatory cytokines (TNFα, IL-1β, IL-6, IL-8, shown that phagocytosis of titanium nano-and microparticles up-regulates the expression of TNFα, IL-1β and IL-6 on both mRNA and protein levels (Beidelschies et al, 2008, Luo et al, 2016, Minematsu et al, 2007, Naganuma et al, 2016, Pajarinen et al, 2013, Rakshit et al, 2006, Ruiz et al, 2016, Valles et al, 2006, Yazdi et al, 2010. Additionally, the inflammasome protein NLPR3 which is responsible for IL-1β and IL-18 activation (Martinon et al, 2002), is also up-regulated in macrophages by titanium (Naganuma et al, 2016, Ruiz et al, 2016, Yazdi et al, 2010.…”