Background/Purpose: Systemic sclerosis (SSc) is an autoimmune disease, which is characterized by inflammation, fibrosis and vasculopathy in multiple organs, mainly in the lung, heart and skin. Neurotrophins (NTs) are a family of proteins promoting neuron growth and survival; however their profibrotic and proangiogenic actions were recently discovered in fibroblasts and endothelial cells. Elevated number of monocytes and their activation state has been already reported in SSc, but detailed roles of monocytes in multiorgan fibrogenesis in SSc remain unclear. We aimed to determine the contribution and the role of circulating monocytes in the onset and progression of multiorgan fibrosis in SSc. Additionally, we investigated the involvement of neurotrophin-3 (NT-3) and neurotrophins receptors in the fibrogenesis in SSc.

Methods: Endomyocardial biopsies from SSc patients and healthy controls were screened by immunohistochemistry. CD14⁺ monocytes isolated from peripheral blood of SSc patients and healthy donors were differentiated towards the myofibroblast phenotype by stimulation with TGFβ1, IL-4, IL-10 and IL-13. In addition, CD14⁺ monocytes were co-cultured with dermal fibroblasts originated from SSc patients and healthy subjects, and with adult cardiac fibroblasts. After 7 days, myofibroblast gene expression and cytokine secretion profiles were evaluated by qPCR, Western blot, protein array and ELISA. Healthy and SSc dermal or cardiac fibroblasts were stimulated with NT-3 and induction of profibrotic genes was analysed by qPCR and immunofluorescence.

Results: Myocardium of SSc patients revealed the presence of CD45-expressing infiltrates, extended collagen I deposition and the presence of CD14-expressing elongated cells in the fibrotic tissue. Stimulated monocytes acquired myofibroblast-like phenotype with increased expression of collagen I (p<0.0001), fibronectin (p<0.05), and α smooth muscle actin (α-SMA) in comparison to untreated cells. Similarly, CD14⁺ monocytes exposed to dermal or cardiac fibroblasts acquired spindle shape and expressed higher levels of profibrotic genes. The process of monocyte to myofibroblast differentiation employed TGFβ/SMAD signalling. Blocking of the TGFBR1 receptor and canonical SMAD-dependent pathway with inhibitors resulted in the abrogation of extracellular matrix secretion by monocytes. CD14⁺ monocytes from SSc patients were characterised by higher secretion of CXCL10 (p<0.001), CCL20, CCL22, Leukemia Inhibitory Factor (LIF) and NT-3. SSc fibroblasts revealed higher expression of TrkB and p75^NTR receptors. Moreover, elevated level of α-SMA was observed in SSc fibroblasts after stimulation with NT-3.

Conclusion: Here we demonstrated the capability of peripheral blood monocytes to differentiate towards the functional myofibroblast phenotype, indicating these cells as one of the potential sources of pathological tissue myofibroblasts in SSc. Additionally, SSc monocytes secreted NT-3, which induced fibroblast to myofibroblast differentiation. Further studies of TGFβ induced NT-3 expression in monocytes and its effects on fibroblast to myofibroblast differentiation might lead to novel treatment strategies.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/monocytesneurotrophinsmyofibroblasts-as-a-novel-axis-in-systemic-sclerosis/