The IRE1α Arm of UPR Regulates Muscle Cells Immune Characters by Restraining p38 MAPK Activation

Abstract

Skeletal muscle repair and systemic inflammation/immune responses are linked to endoplasmic reticulum stress (ER stress) pathways in myopathic muscle, and muscle cells play an active role in muscular immune reactions by exhibiting immunological characteristics under persistent proinflammation stimuli. Whether ER stress affects the intrinsic immunological capacities of myocytes in the inflammatory milieu, as it does to immune cells, and which arms of the unfolded protein response (UPR) mainly participate in these processes remain mostly unknown. We investigated this issue and showed that inflammatory stimuli can induce the activation of the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) and inositol-requiring enzyme 1α (IRE1α) arms of the UPR in myocytes both in vivo and in vitro. UPR stressor administration reversed the increased IFN-γ-induced expression of the MHC-II molecule H2-Ea, the MHC-I molecule H-2Kb, toll-like receptor 3 (TLR3) and some proinflammatory myokines in differentiated primary myotubes in vitro. However, further IRE1α inhibition thoroughly corrected the trend in the UPR stressor-triggered suppression of immunobiological molecules. In IFN-γ-treated myotubes, dramatic p38 MAPK activation was observed under IRE1α inhibitory conditions, and the pharmacological inhibition of p38 reversed the immune molecule upregulation induced by IRE1α inhibition. In parallel, our coculturing system verified that the ovalbumin (OVA) antigen presentation ability of inflamed myotubes to OT-I T cells was enhanced by IRE1α inhibition, but was attenuated by further p38 inhibition. Thus, the present findings demonstrated that p38 MAPK contributes greatly to IRE1α arm-dependent immunobiological suppression in myocytes under inflammatory stress conditions.

IRE1α arm of unfolded protein response in muscle-specific TGF-β signaling-mediated regulation of muscle cell immunological properties

“…The p38 MAPK could be activated at post stages of myogenesis, leading to promotion of muscle gene expression [ 2 ]. Our previous work has also noticed that p38 MAPK was notably activated by inhibiting IRE1α in myofibers with the stimulation of IFN-γ [ 15 ]. This study has further demonstrated that the upregulation of immunological molecules in myofibers, induced by 4μ8C, was reversed by inhibiting p38 MAPK, which means that p38 MAPK would have a pivotal role in regulating immunological molecules of myofibers by the IRE1α pathway.…”

“…For proinflammatory stimuli, lipopolysaccharide (LPS, 100 ng/ml, R&D Systems, USA) and IFN-γ (3 ng/ml, R&D Systems, USA) were added to the fresh medium. To inhibit UPR, MPC-myotubes were treated with 4-phenyl butyric acid (4-PBA) (10 mM, UPR inhibitor, Selleck, Shanghai, China), 4μ8c (50 mM, IRE1α pathway inhibitor, Selleck), or GSK2606414 (1 mM, PERK pathway inhibitor, which can directly bind to PERK and inhibits its activity, Selleck) for about 4 h [ 15 , 29 ]. For activating UPR, MPC-myotubes were treated with tunicamycin (TM, 1 mg/ml, Santa Cruz California, USA) or thapsigargin (Tg, 0.2 mmol/l, Santa Cruz) for about 4 h [ 15 , 30 , 31 ].…”

“…To inhibit UPR, MPC-myotubes were treated with 4-phenyl butyric acid (4-PBA) (10 mM, UPR inhibitor, Selleck, Shanghai, China), 4μ8c (50 mM, IRE1α pathway inhibitor, Selleck), or GSK2606414 (1 mM, PERK pathway inhibitor, which can directly bind to PERK and inhibits its activity, Selleck) for about 4 h [ 15 , 29 ]. For activating UPR, MPC-myotubes were treated with tunicamycin (TM, 1 mg/ml, Santa Cruz California, USA) or thapsigargin (Tg, 0.2 mmol/l, Santa Cruz) for about 4 h [ 15 , 30 , 31 ]. For blocking p38 activity, MPC-myotubes were cultured with SB202190 (20 mM, Sigma) for 4 h [ 15 , 32 ].…”

“…For activating UPR, MPC-myotubes were treated with tunicamycin (TM, 1 mg/ml, Santa Cruz California, USA) or thapsigargin (Tg, 0.2 mmol/l, Santa Cruz) for about 4 h [ 15 , 30 , 31 ]. For blocking p38 activity, MPC-myotubes were cultured with SB202190 (20 mM, Sigma) for 4 h [ 15 , 32 ]. For re-activating the TGF-β/Smad signaling pathway, MPC-myotubes were cultured with SRI-011381 hydrochloride (SRI, 8 μg/ml, MedChemExpress, USA) for about 4 h [ 33 ].…”

Hidden Agenda - The Involvement of Endoplasmic Reticulum Stress and Unfolded Protein Response in Inflammation-Induced Muscle Wasting

“…The ER stress inducing agents tunicamycin and thapsigargin prevented the IFN-γ-induced expression of MHCII and MHCI molecules. Inhibition of IRE1α attenuated the UPR stressor-mediated reduction of these immunobiological molecules ( 141 ). These data indicate that the IRE1α arm mediates immunobiological suppression in myocytes during inflammation.…”