SOX9 plays an essential role in myofibroblast driven hepatic granuloma integrity and parenchymal repair during schistosomiasis-induced liver damage
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Schistosomiasis is a neglected, and potentially lethal, parasitic disease that affects hundreds of millions of people worldwide. As part of the schistosome lifecycle, parasite eggs accumulate within the liver where they evoke intense granulomatous pathology, typified by a dense extracellular matrix (ECM) barrier, which serves to contain toxic egg secretions. In severe cases, this progressive and irreversible egg-evoked ECM deposition can lead to pathological scarring, impaired liver function and lethality. Thus, identifying the core regulators that govern ECM deposition may aid discovery of new therapeutic targets for schistosomiasis. The transcription factor Sex determining region Y-box 9 (Sox9) is a known regulator of pathological scaring. We found that, following Schistosoma mansoni infection, SOX9 was ectopically expressed in myofibroblasts within the granuloma and in surrounding hepatocytes. In the absence of SOX9, granuloma size was significantly diminished, and mice failed to produce a robust ECM barrier around eggs, resulting in more diffuse liver injury and scattered distribution of immune cells. Immunologically, SOX9 loss in both naïve and infected mice led to an increase in hepatic neutrophil and monocyte proportions, with the expansion of Ly6c lo monocyte populations in infected SOX9 deficient mice only. Infected SOX9–deficient mice also displayed exaggerated Type 2 inflammation, including pronounced eosinophilia. These data highlight the importance of SOX9 for intact hepatic granuloma formation during schistosomiasis and suggest SOX9 or its related factors may provide attractive future targets for meeting the clinical need to limit and/or reverse fibrotic disease.
Author Summary
Mammalian infection with schistosome worms results in the deposition of parasite eggs in the liver, where they secrete organ damaging toxins. In response, the liver generates a cellular granuloma barrier rich in extracellular matrix to limit these secretions and protect the overall organ. As in other liver injuries, SOX9 becomes progressively expressed in multiple cell types during the time course of schistosome infection. To understand the role of SOX9 in the liver response to schistosomes we utilised a global SOX9 deficient mouse model. These mice show reduced and disorganised granuloma formation during schistosome infection, with disrupted hepatic immune profiles. This suggests that SOX9 is required to form a robust and coordinated granuloma barrier that limits liver damage in this important but neglected parasitic disease.
