LPS Induces Active HMGB1 Release From Hepatocytes Into Exosomes Through the Coordinated Activities of TLR4 and Caspase-11/GSDMD Signaling

Abstract

High-mobility group box-1 (HMGB1), a ubiquitous nuclear protein, acts as a late mediator of lethality when released extracellularly during sepsis. The major source of circulating HMGB1 in sepsis is hepatocytes. However, the mechanism of HMGB1 release of hepatocytes during sepsis is not very clear. We have previously shown that bacterial endotoxin [lipopolysaccharide (LPS)] sensing pathways, including Toll-like receptor (TLR)4 and caspase-11, regulate hepatocyte HMGB1 release in response to LPS. Here, we report the novel function of caspase-11 and gasdermin D (GsdmD) in LPS-induced active HMGB1 released from hepatocytes. HMGB1 release during endotoxemia was caspase-11/GsdmD dependent via an active way in vivo and in vitro. Caspase-11/GsdmD was responsible for HMGB1 translocation from nucleus to the cytoplasm via calcium changing-induced phosphorylation of calcium-calmodulin kinase kinase (camkk)β during endotoxemia. Cleaved GsdmD accumulated on the endoplasmic reticulum, suggesting this may lead to calcium leak and intracellular calcium increase. Furthermore, we investigated that exosome was an important pathway for HMGB1 release from hepatocytes; this process was dependent on TLR4, independent of caspase-11 and GsdmD in vivo and in vitro. These findings provide a novel mechanism that TLR4 signaling results in an increase in caspase-11 expression, as well as increased exosome release, while caspase-11/GsdmD activation/cleavage leads to accumulation of HMGB1 in the cytoplasm through a process associated with the release of calcium from the endoplasmic reticulum and camkkβ activation.

SARS-CoV-2: Is the liver merely a bystander to severe disease?

“…pyroptosis). 3 Indeed, the authors demonstrate TUNEL-positive hepatocytes (not specific for apoptosis, but also positive in non-apoptotic cell death and autolysis 4 ) and elevated lactate dehydrogenase levels (a marker of non-apoptotic cell death), supporting pyroptosis and autolysis as alternate explanations for these clinical and tissue findings, respectively. Moreover, as the authors acknowledge, hepatocytes express little to no angiotensin converting enzyme-2 (ACE2) receptors, the cellular entry point for SARS-CoV-2.…”

Galectin-8 senses phagosomal damage and recruits selective autophagy adapter TAX1BP1 to control Mycobacterium tuberculosis infection in macrophages

“…4A). Interestingly, we identified several proteins that, like galectins, are secreted through a noncanonical pathway that does not require a signal sequence, including HGMB1 (Gardella et al, 2002;Li et al, 2020). Also identified were a panel of proteins associated with exosome secretion, a form of noncanonical secretion, including syntenin-1/SDCBP, HSP90AA1, HSP90B1, ANXA1, ANXA2, ANXA5, 14-3-3-epsilon/YWAHAE, and 14-3-3-gamma/YWAHAG (Baietti et al, 2012;Gonzalez-Begne et al, 2009;Guha et al, 2019;Lauwers et al, 2018).…”

Exosomes in Sepsis

“…Consistent with the elevated HMGB1 levels in sepsis patients, exosomes released from cells challenged with LPS or infected with pathogen contain increased levels of HMGB1 ( 24 , 31 ). In addition, injection of GW4869, exosome inhibitor, or knockdown of Rab27, a GTPase required for exosome release, into LPS-challenged mice resulted in significant lower levels of HMGB1 in the plasma, suggesting the importance of exosomes as couriers of HMGB1 during sepsis ( 31 ). Several mechanisms of the release of exosomal HMGB1 from cells have been revealed so far, such as the activation of TLR4 and caspase-11/gasdermin D (GSDMD) signaling, decreased autophagy and endoplasmic reticulum (ER) stress, all of which are important cellular mechanisms of sepsis pathophysiology ( 31 – 33 ).…”

“…High mobility group box 1 is a nuclear protein which regulates gene expression and chromatin architecture intracellularly, but is also known as a DAMP once it is released into the extracellular space (3). Consistent with the elevated HMGB1 levels in sepsis patients, exosomes released from cells challenged with LPS or infected with pathogen contain increased levels of HMGB1 (24,31). In addition, injection of GW4869, exosome inhibitor, or knockdown of Rab27, a GTPase required for exosome release, into LPS-challenged mice resulted in significant lower levels of HMGB1 in the plasma, suggesting the importance of exosomes as couriers of HMGB1 during sepsis (31).…”