Targeting early PKCθ‐dependent T‐cell infiltration of dystrophic muscle reduces disease severity in a mouse model of muscular dystrophy

Abstract

Chronic muscle inflammation is a critical feature of Duchenne muscular dystrophy and contributes to muscle fibre injury and disease progression. Although previous studies have implicated T cells in the development of muscle fibrosis, little is known about their role during the early stages of muscular dystrophy. Here, we show that T cells are among the first cells to infiltrate mdx mouse dystrophic muscle, prior to the onset of necrosis, suggesting an important role in early disease pathogenesis. Based on our comprehensive analysis of the kinetics of the immune response, we further identify the early pre-necrotic stage of muscular dystrophy as the relevant time frame for T-cell-based interventions. We focused on protein kinase C θ (PKCθ, encoded by Prkcq), a critical regulator of effector T-cell activation, as a potential target to inhibit T-cell activity in dystrophic muscle. Lack of PKCθ not only reduced the frequency and number of infiltrating T cells but also led to quantitative and qualitative changes in the innate immune cell infiltrate in mdx/Prkcq muscle. These changes were due to the inhibition of T cells, since PKCθ was necessary for T-cell but not for myeloid cell infiltration of acutely injured muscle. Targeting T cells with a PKCθ inhibitor early in the disease process markedly diminished the size of the inflammatory cell infiltrate and resulted in reduced muscle damage. Moreover, diaphragm necrosis and fibrosis were also reduced following treatment. Overall, our findings identify the early T-cell infiltrate as a therapeutic target and highlight the potential of PKCθ inhibition as a therapeutic approach to muscular dystrophy. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Targeting PKCθ Promotes Satellite Cell Self-Renewal

“…We previously showed that knock-out of PKCθ or its inhibition in a mouse model of Duchenne Muscular Dystrophy (mdx mouse) reduces muscle damage, by modulating the immune cell infiltration. This beneficial effect was mainly due to the inhibition of PKCθ in T cells, which leads to reduced inflammation [10][11][12]. Interestingly, we also found that lack of PKCθ promotes muscle repair in dystrophic mice, even at advanced stages of the disease, supporting SCs survival and maintenance [13].…”

“…We next sought to validate our results from the PKCθ-/-mouse model, using the C20specific inhibitor of PKCθ [11,12,18,19]. To analyze the effects of C20 throughout the different phases of myogenic progression, we isolated SC from WT and PKCθ-/-mice and cultured them for 4 days in growth medium (GM), followed by 2 days in differentiation medium (DM).C20 was used at the concentration range (0.5 µM, 1 µM and 2 µM) we previously found not to be toxic for in vitro treatment [11].…”

“…The treatment was started one day prior to the CTX injection, and was continued for 10 days following injury, during the phase of satellite cell activation, proliferation and differentiation ( Figure 5G). The mice were treated with daily intra peritoneal injections of C20, at a dose of 5 mg/Kg (previously established to be effective in vivo [12]). Control mice were treated with Vehicle (DMSO) at the same concentration used to dissolve C20 (0.5% final concentration in the injected volume).…”

Lack of PKCθ Promotes Regenerative Ability of Muscle Stem Cells in Chronic Muscle Injury

“…This observation suggests that the up regulation of Delta1 and Jagged1 expression is due to lack of PKCθ in myofibers and not to different muscle environment. In fact, PKCθ is crucial for the adaptive immune response in chronic muscle injury where T cells are involved but, in acute muscle injury, lack of PKCθ does not alter the innate immune response (myeloid cell recruitment) that is important during the regenerating process [21].…”

“…We previously showed that lack or pharmacological inhibition of PKCθ reduced muscle loss and inflammation, and increased muscle regeneration and performance in mdx mice. The observed phenotype was primarily due to lack of PKCθ in hematopoietic cells [19,20], and in particular inhibition of early T cells infiltration in dystrophic muscle [21]. However, PKCθ is also expressed in muscle, where it modulates several signalling pathways involved in foetal and early post-natal tissue growth and maturation [22][23][24].…”