Bivona Iii Joseph J, Mank Madeleine M, Stapleton Renee D, Files D Clark, Toth Michael J, Poynter Matthew E
Department of Medicine and Vermont Lung Center, University of Vermont Larner College of Medicine, Burlington, VT, United States.
Department of Internal Medicine, Section on Pulmonary, Critical Care, Allergy and Immunology, Wake Forest School of Medicine, Winston-Salem, NC, United States.
Front Pharmacol. 2022 Jun 23;13:917917. doi: 10.3389/fphar.2022.917917. eCollection 2022.
The abundance, anatomical distribution, and vascularity of skeletal muscle make it a potentially important contributor to local cytokine production and systemic cytokine abundance during inflammatory events. An orchestrated balance between the production of pro- and anti-inflammatory mediators is necessary for proper immune function, yet the contribution of the body's largest organ system, comprised primarily of skeletal muscle myocytes that fuse to form myofibers, to this process is largely unknown. Endotoxin (lipopolysaccharide, LPS) stimulates toll-like receptor 4 (TLR4) to induce the production of several pro-inflammatory cytokines, including interleukin-6 (IL-6) and C-C motif chemokine ligand 2 (CCL2), by a of myriad cell types. We sought to quantify the influence of myofibers on systemic cytokine concentrations following an acute endotoxemia challenge. To accomplish this, we generated muscle specific conditional knockouts for TLR4 (TLR4SMKO), IL-6 (IL6SMKO), and CCL2 (CCL2SMKO). We administered low concentrations of intravenous LPS (IV LPS) to these receptor and effector knockout mice and collected samples after 3 h. Using gene expression analysis of gastrocnemius muscle and serum cytokine measurements after IV LPS, we determined that deletion of myofiber IL-6 or CCL2 led to a 93% and 57% reduction of these specific cytokines in the systemic circulation, respectively. Myofiber specific TLR4 deletion decreased the expression of IL-6, CCL2, and C-X-C motif chemokine ligand 1 (CXCL1) in the gastrocnemius muscle. These data indicate the critical involvement and direct contribution of myofibers during the early systemic inflammatory cytokine response to endotoxin.
骨骼肌的丰富程度、解剖分布和血管分布使其在炎症事件中可能成为局部细胞因子产生和全身细胞因子丰度的重要贡献者。促炎和抗炎介质的产生之间需要精心协调的平衡才能实现正常的免疫功能，然而，这个主要由融合形成肌纤维的骨骼肌肌细胞组成的人体最大器官系统在这一过程中的作用在很大程度上尚不清楚。内毒素（脂多糖，LPS）刺激Toll样受体4（TLR4），通过多种细胞类型诱导包括白细胞介素-6（IL-6）和C-C基序趋化因子配体2（CCL2）在内的几种促炎细胞因子的产生。我们试图量化急性内毒素血症挑战后肌纤维对全身细胞因子浓度的影响。为了实现这一目标，我们构建了TLR4（TLR4SMKO）、IL-6（IL6SMKO）和CCL2（CCL2SMKO）的肌肉特异性条件性敲除小鼠。我们向这些受体和效应器敲除小鼠静脉注射低浓度的LPS（IV LPS），并在3小时后采集样本。通过对腓肠肌的基因表达分析和IV LPS后的血清细胞因子测量，我们确定肌纤维IL-6或CCL2的缺失分别导致全身循环中这些特定细胞因子减少93%和57%。肌纤维特异性TLR4缺失降低了腓肠肌中IL-6、CCL2和C-X-C基序趋化因子配体1（CXCL1）的表达。这些数据表明肌纤维在内毒素引起的早期全身炎症细胞因子反应中起关键作用并做出直接贡献。
