Cytosolic HMGB1 Mediates LPS-Induced Autophagy in Microglia by Interacting with NOD2 and Suppresses Its Proinflammatory Function

Abstract

The high mobility group box 1 (HMGB1), a well-known danger-associated molecule pattern (DAMP) molecule, is a non-histone chromosomal protein localized in the nucleus under normal physiological conditions. HMGB1 exhibits diverse functions depending on its subcellular location. In the present study, we investigated the role of HMGB1-induced autophagy in the lipopolysaccharide (LPS)-treated BV2 microglial cell line in mediating the transition between the inflammatory and autophagic function of the nucleotide-binding oligomerization domain-containing 2 (NOD2), a cytoplasmic pattern-recognition receptor. The induction of the microtubule-associated protein 1 light chain 3 (LC3), an autophagy biomarker, was detected slowly in BV2 cells after the LPS treatment, and peak induction was detected at 12 h. Under these conditions, NOD2 level was significantly increased and the binding between HMGB1 and NOD2 and between HMGB1 and ATG16L1 was markedly enhanced and the temporal profiles of the LC3II induction and HMGB1-NOD2 and HMGB1-ATG16L1 complex formation coincided with the cytosolic accumulation of HMGB1. The LPS-mediated autophagy induction was significantly suppressed in BV2 cells after HMGB1 or NOD2 knock-down (KD), indicating that HMGB1 contributes to NOD2-mediated autophagy induction in microglia. Moreover, NOD2-RIP2 interaction-mediated pro-inflammatory cytokine induction and NF-κB activity were significantly enhanced in BV2 cells after HMGB1 KD, indicating that HMGB1 plays a critical role in the modulation of NOD2 function between pro-inflammation and pro-autophagy in microglia. The effects of the cell-autonomous pro-autophagic pathway operated by cytoplasmic HMGB1 may be beneficial, whereas those from the paracrine pro-inflammatory pathway executed by extracellularly secreted HMGB1 can be detrimental. Thus, the overall functional significance of HMGB1-induced autophagy is different, depending on its temporal activity.

Age-Dependent and Aβ-Induced Dynamic Changes in the Subcellular Localization of HMGB1 in Neurons and Microglia in the Brains of an Animal Model of Alzheimer’s Disease

“…Nuclear and cytoplasmic extract preparation was performed as previously described [23]. Brain tissue blocks from the frontal cortices and striata were obtained surgically.…”

Protective Effects of Sophorae tonkinensis Gagnep. (Fabaceae) Radix et Rhizoma Water Extract on Carbon Tetrachloride-Induced Acute Liver Injury

“…HMGB1 is an inflammatory cytokine and key endogenous danger signal molecule in the nucleus [35]. TNF-α, IL-6, and IL-1β are common pro-inflammatory factors.…”

Receptor-interacting protein kinase 2 (RIPK2) profoundly contributes to post-stroke neuroinflammation and behavioral deficits with microglia as unique perpetrators

“…RIPK2 serves as the primary downstream signaling kinase for the nucleotide-binding oligomerization domain (NOD) 1 and NOD2 PRRs [16]. NOD1/2 receptors have been most notably characterized for their roles in recognizing PAMPs; however, more recent evidence suggests that these receptors may play a more prominent role in recognizing DAMPs than was previously thought [16][17][18]. RIPK2 is involved in both nuclear factor kappa-lightchain-enhancer of activated B cells (NF-κB) activation and the initiation of caspase-mediated apoptosis via the interaction between RIPK2's caspase activation and recruitment domain (CARD) and caspase-1 [19,20].…”