Of Mice and Men

Abstract

The molecular basis responsible for tolerance following inflammatory response to LPS is not well-understood. We hypothesized that inflammation/tolerance in monocytes/ macrophages is dependent on the proteases of proteasome. To test our hypothesis, first, we examined the expression of different proteasome subunits in different human and mouse monocytes/macrophages. Secondly, we investigated the effect of proteasome subunits/ proteases on LPS-induced expression of tumor necrosis factor-α (TNF-α) and nitric oxide (NO) during inflammation and tolerance using mouse RAW 264.7 macrophages, THP1 cells, and cluster of differentiation 14 positive (CD14+) human monocytes. We found that RAW 264.7 cells (XYZ), mouse peritoneal resident, thioglycollate-elicited macrophages, primed RAW 264.7 (XYZ, LMP) and human monocytes (LMP) expressed different types of proteasome subunits/activities. Cells containing predominantly either LMP subunits (such as THP-1 and human monocytes), or only X, Y, Z subunits (RAW 264.7 cells not primed) could only induce TNF-α, but not NO, while cells containing all five-six subunits (XYZ, LMP) of the proteasome could induce both mediators in response to LPS. Distinct states of inflammation/tolerance in LPS treated cells, strongly correlated with an upregulation or downregulation of proteasome's subunits (proteases), respectively. Moreover, interferon-γ (IFN-γ) treatment of tolerant cells caused robust induction of proteasome's subunit expression in mouse macrophages and human monocytes, and cells regained their ability to respond to LPS. These studies are vital for understanding function of proteasome's subunits during inflammation/tolerance in mouse and human cells, and for design of therapeutic strategies for all diseases based on inflammation.

Less Severe Polymicrobial Sepsis in Conditional mgmt-Deleted Mice Using LysM-Cre System, Impacts of DNA Methylation and MGMT Inhibitor in Sepsis

“…Despite several functions of the proteasome in cell homeostasis, the 26S proteasome regulates DNA repair by degrading the proteins or acting as a molecular chaperone to promote the disassembly of the repair complex [ 54 ]. Increased proteasome in LPS-activated macrophages indirectly indicates an increased abundance of unneeded proteins after LPS stimulation supporting previous publications [ 72 , 73 ].…”

Resveratrol Downregulates Biomarkers of Sepsis Via Inhibition of Proteasome's Proteases

“…In addition, by blocking proteasome activities, most of the other proteins degraded by this complex would also be expected to be stabilized and accumulate in the cell. Since the proteasome regulates both inflammation/tolerance in the cell [4, 10], overall, our study supports the use of resveratrol as a potential natural therapeutic drug for treating inflammatory diseases during the early stages of sepsis and other autoimmune diseases.…”

“…Our previous work established that initial interaction of LPS and monocytes/macrophages induces all three proteasome activities, thus initiating a process of proteasome-mediated degradation of signaling mediators such as TLR4, IRAK-1, IRAKM, phosphorylated interferon regulatory factor 3 (P-IRF3) [10, 11]. This leads to a net increase in ubiquitinated proteins and activation of transcription factors, such as NF-κB (proteasome degrades its inhibitor IκB) thus causing inflammation.…”

“…In our recent communication [4], we have reported that biomarkers VCAM-1, ICAM1, CRP, and resistin, are upregulated in plasmas of septic patients. Moreover, during LPS-induced inflammatory phase, there is an increased expression of immunoproteasome subunits [10]. Therefore, resveratrol (not a specific inhibitor) and LMP7 specific inhibitor ONX-0914 were tested for downregulating these LPS-induced biomarkers.…”

Single cell RNA sequencing identifies unique inflammatory airspace macrophage subsets

“…In comparison, cluster 3 is characterized by expression of enzymes involved in protein processing and antigen presentation, raising the possibility that cells in this cluster are programmed for functions distinct from those of cluster 4 -despite existing in a shared microenvironment. Indeed, altered ratios of constitutive versus immunoproteosomal subunit transcripts in cluster 4 compared with cluster 3 are in keeping with the emerging role of proteosomal protease activities as master regulators of the inflammatory response (49)(50)(51)(52)(53). Given that several of the DEGs that distinguish cluster 4 from cluster 3 are also expressed in neutrophils at steady-state (S100a9, Lcn2, Il2r) (38), we considered whether this population may represent macrophage/neutrophil complexes (i.e., doublets containing 2 cells bound together).…”