Bone Components Downregulate Expression of Toll-Like Receptor 4 on the Surface of Human Monocytic U937 Cells: A Cell Model for Postfracture Immune Dysfunction.

Jui-An Lin,Feng-Yen Lin,Ta-Liang Chen

doi:10.1155/2015/896576

Jui-An Lin, Feng-Yen Lin + Show 1 more

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https://doi.org/10.1155/2015/896576

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Abstract

To mimic the immune status of monocyte in the localized fracture region, toll-like receptor 4 (TLR4) surface expression in human monocytic U937 cells was used as the main target to assess immune dysfunction following bone component exposure. We first identified the effects of bone components (including the marrow content) on TLR4 surface expression and then examined the mechanisms underlying the changes. The level of microRNA-146a expression, an indicator of endotoxin tolerance, was also assayed. Bone component exposure downregulated TLR4 surface expression at 24 h by flow cytometry analysis, compatible with the result obtained from the membranous portion of TLR4 by western blot analysis. The cytoplasmic portion of TLR4 paradoxically increased after bone component exposure. Impaired TLR4 trafficking from the cytoplasm to the membrane was related to gp96 downregulation, as observed by western blot analysis, and this was further evidenced by gp96-TLR4 colocalization under confocal microscopy. TaqMan analysis revealed that the expression of microRNA-146a was also upregulated. This cell model demonstrated that bone component exposure downregulated TLR4 surface expression in a gp96-related manner in human monocytic U937 cells, an indicator of immunosuppression at 24 h. Immune dysfunction was further evidenced by upregulation of microRNA-146a expression at the same time point.

Highlights

Based on projections of economic and social development, it is estimated that, by 2030, trauma will account for one of the major disease burdens worldwide, possibly even ahead of ischemic heart disease [1]
Total toll-like receptor 4 (TLR4) protein expression was not affected by bone component exposure (Figure 3), validating the fact that regional changes in TLR4 could account for the downregulation of its surface expression
The expression of the membranous portion of the TLR4 protein decreased in cells treated with a moderately high concentration (50 ng/mL) of bone components, which was consistent with the flow cytometry result

Summary

Introduction

Based on projections of economic and social development, it is estimated that, by 2030, trauma will account for one of the major disease burdens worldwide, possibly even ahead of ischemic heart disease [1]. Trauma is the leading cause of death among people aged 15 through 44 years [2, 3]. Sepsis after trauma increases the rate of organ failure and in-hospital mortality. Despite advances in trauma care and research, the incidence of posttraumatic sepsis still remained as high as 10% over the last decade [4]. The general lack of effective therapeutic options for trauma patients is mainly due to the complexity of interacting inflammatory and physiological components at multiple levels [5, 6]. Focusing on the impact of individual components helps to evaluate trauma conditions in depth

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