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In Duchenne muscular dystrophy (DMD), a dysregulated extracellular matrix (ECM) directly exacerbates pathology. Glucocorticoids are beneficial therapeutics in DMD, and have pleiotropic effects on the composition and processing of ECM proteins in other biological contexts. The synthesis and remodelling of a transitional versican-rich matrix is necessary for myogenesis; whether glucocorticoids modulate this transitional matrix is not known. Here, versican expression and processing were examined in hindlimb and diaphragm muscles from mdx dystrophin-deficient mice and C57BL/10 wild type mice. V0/V1 versican (Vcan) mRNA transcripts and protein levels were upregulated in dystrophic compared to wild type muscles, especially in the more severely affected mdx diaphragm. Processed versican (versikine) was detected in wild type and dystrophic muscles, and immunoreactivity was highly associated with newly regenerated myofibres. Glucocorticoids enhanced C2C12 myoblast fusion by modulating the expression of genes regulating transitional matrix synthesis and processing. Specifically, Tgfβ1, Vcan and hyaluronan synthase-2 (Has2) mRNA transcripts were decreased by 50% and Adamts1 mRNA transcripts were increased three-fold by glucocorticoid treatment. The addition of exogenous versican impaired myoblast fusion, whilst glucocorticoids alleviated this inhibition in fusion. In dystrophic mdx muscles, versican upregulation correlated with pathology. We propose that versican is a novel and relevant target gene in DMD, given its suppression by glucocorticoids and that in excess it impairs myoblast fusion, a process key for muscle regeneration.

Extracellular matrix (ECM) enzymes including the ADAMTS (A disintegrin-like and metalloproteinase with thrombospondin-1 motifs) family have been shown to regulate influenza-specific immunity. ADAMTS7, a largely uncharacterised ECM enzyme with broad tissue distribution has been associated with coronary heart disease and arthritis, however its role in viral immunity remains undefined. We assessed the contribution of ADAMTS7 to influenza-specific immunity using Adamts7−/− mice. Adamts7−/− mice intranasally infected with influenza virus showed increased weight loss and had higher viral loads when compared to WT controls. We also observed fewer influenza-specific CD8+ T cells and changes in cytokine production following primary and secondary infection suggesting ADAMTS7 expression is a key regulator of viral immunity.

Members of the ADAMTS (A disintegrin-like and metalloproteinase with thrombospondin-1 motifs) metalloproteinase family remodel the extracellular matrix (ECM). In this current study we demonstrate that Adamts5−/− mice infected with X31 influenza virus (104pfu/mouse) show enhanced weight loss, have higher virus titres and perturbed T cell immunity when compared to WT counterparts. These responses correlate with the accumulation of a key ADAMTS5 substrate, versican, in the MLN of Adamts5−/− mice and underpin disruption of T cell migration as evidenced through the use of both in vitro and in vivo models. Our research emphasizes the importance of ADAMTS5 activity in the control of influenza virus infection and highlights the potential for development of ADAMTS5-based therapeutic strategies to reduce overall morbidity and mortality.

Extracellular matrix (ECM) enzymes, such as the ADAMTS (A disintegrin-like and metalloproteinase with thrombospondin-1 motifs) family, play a significant role in ECM remodelling. ECM remodelling facilitates immune cell migration and adhesion. ADAMTS5, a member of the ADAMTS family, cleaves ECM proteoglycans, such as aggrecan and versican, and has a well-characterised role in osteoarthritis and embryogenesis. However, ADAMTS5 has an un-identified role throughout the immune response. Our previous studies indicated that ADAMTS5 expression is required to mediate T cell migration during acute influenza virus infection. In this current study, we analysed secondary acute responses (day 7) and primary memory (day 30) following influenza infection of Adamts5−/− mice. Here, we primed Adamts5−/− mice with PR8 influenza virus (1.5×107 pfu/mouse) and challenged 8 weeks later with X31 influenza virus (104 pfu/mouse). Following secondary infection, Adamts5−/− mice displayed greater weight loss and expressed fewer IFNγ+NP366-372+CD8+T cells. Critically, we observed a reduced number of influenza-specific CD8+ memory cells (CD62LhiCD44lo) in Adamts5−/− mice after primary infection, which may result in the lower number of IFNγ+NP366-372+CD8+T cells observed in secondary acute infection. We therefore hypothesize that the ADAMTS5 enzyme, through its ECM remodelling capabilities, is essential for the maintenance of memory and recall of functional immunity following secondary infection.

Members of the ADAMTS (A disintegrin-like and metalloproteinase with thrombospondin-1 motifs) metalloproteinase family remodel the extracellular matrix (ECM) to facilitate immune cell migration and cell adhesion. In this current study, we infected Adamts5−/− mice with X31 influenza virus (104pfu/mouse)and measured weight loss, viraemia and T cell immunity following acute infection. Adamts5−/− mice showed greater weight loss and increased viraemia when compared to WT counterparts. Furthermore, we observed reduced NP366 and PA224 influenza specific CD8+ T cells in the spleen and lungs of Adamts5−/− mice with a corresponding accumulation of these T cell specificities in the mediastinal lymph node (MLN) 10 days post infection. Critically, these responses correlated with increased expression of a key ADAMTS5 substrate; versican, in the MLNs of Adamts5−/− mice. We therefore hypothesize that versican accumulation in the MLNs of Adamts5−/− mice results in T cell accumulation and that ADAMTS5 is a key enzyme involved in facilitating T cell migration from the MLN to the periphery following acute influenza virus infection.