Role of fibroblast specific protein 1 expression in the progression of adriamycin-induced glomerulosclerosis

Effect of Anti-S100A4 Monoclonal Antibody Treatment on Experimental Skin Fibrosis and Systemic Sclerosis-Specific Transcriptional Signatures in Human Skin

OBJECTIVE

S100A4 is a DAMP protein. S100A4 is overexpressed in patients with systemic sclerosis (SSc), and levels correlate with organ involvement and disease activity. S100A4-/- mice are protected from fibrosis. The aim of this study was to assess the antifibrotic effects of anti-S100A4 monoclonal antibody (mAb) in murine models of SSc and in precision cut skin slices of patients with SSc.

METHODS

The effects of anti-S100A4 mAbs were evaluated in a bleomycin-induced skin fibrosis model and in Tsk-1 mice with a therapeutic dosing regimen. In addition, the effects of anti-S100A4 mAbs on precision cut SSc skin slices were analyzed by RNA sequencing.

RESULTS

Inhibition of S100A4 was effective in the treatment of pre-established bleomycin-induced skin fibrosis and in regression of pre-established fibrosis with reduced dermal thickening, myofibroblast counts, and collagen accumulation. Transcriptional profiling demonstrated targeting of multiple profibrotic and proinflammatory processes relevant to the pathogenesis of SSc on targeted S100A4 inhibition in a bleomycin-induced skin fibrosis model. Moreover, targeted S100A4 inhibition also modulated inflammation- and fibrosis-relevant gene sets in precision cut SSc skin slices in an ex vivo trial approach. Selected downstream targets of S100A4, such as AMP-activated protein kinase, calsequestrin-1, and phosphorylated STAT3, were validated on the protein level, and STAT3 inhibition was shown to prevent the profibrotic effects of S100A4 on fibroblasts in human skin.

CONCLUSION

Inhibition of S100A4 confers dual targeting of inflammatory and fibrotic pathways in complementary mouse models of fibrosis and in SSc skin. These effects support the further development of anti-S100A4 mAbs as disease-modifying targeted therapies for SSc.

S100A4 a classical DAMP as a therapeutic target in fibrosis

Fibrosis regardless of aetiology is characterised by persistently activated myofibroblasts that are contractile and secrete excessive amounts of extracellular matrix molecules that leads to loss of organ function. Damage-Associated Molecular Patterns (DAMPs) are endogenous host-derived molecules that are released from cells dying or under stress that can be triggered by a variety of insults, either chemical or physical, leading to an inflammatory response. Among these DAMPs is S100A4, part of the S100 family of calcium binding proteins that participate in a variety of cellular processes. S100A4 was first described in context of cancer as a pro-metastatic factor. It is now appreciated that aside from its role in cancer promotion, S100A4 is intimately involved in tissue fibrosis. The extracellular form of S100A4 exerts its effects through multiple receptors including Toll-Like Receptor 4 and RAGE to evoke signalling cascades involving downstream mediators facilitating extracellular matrix deposition and myofibroblast generation and can play a role in persistent activation of myofibroblasts. S100A4 may be best understood as an amplifier of inflammatory and fibrotic processes. S100A4 appears critical in systemic sclerosis pathogenesis and blocking the extracellular form of S100A4 in vivo in various animal models of disease mitigates fibrosis and may even reverse established disease. This review appraises S100A4's position as a DAMP and its role in fibrotic conditions and highlight therapeutically targeting this protein to halt fibrosis, suggesting that it is a tractable target.

The role of stromal cells in epithelial-mesenchymal plasticity and its therapeutic potential

The epithelial-mesenchymal transition (EMT) is a critical tumor invasion and metastasis process. EMT enables tumor cells to migrate, detach from their original location, enter the circulation, circulate within it, and eventually exit from blood arteries to colonize in foreign sites, leading to the development of overt metastases, ultimately resulting in death. EMT is intimately tied to stromal cells around the tumor and is controlled by a range of cytokines secreted by stromal cells. This review summarizes recent research on stromal cell-mediated EMT in tumor invasion and metastasis. We also discuss the effects of various stromal cells on EMT induction and focus on the molecular mechanisms by which several significant stromal cells convert from foes to friends of cancer cells to fuel EMT processes via their secretions in the tumor microenvironment (TME). As a result, a better knowledge of the role of stromal cells in cancer cells' EMT may pave the path to cancer eradication.

Renoprotective effects of extracellular fibroblast specific protein 1 via nuclear factor erythroid 2-related factor-mediated antioxidant activity

Podocyte expression of fibroblast specific protein 1 (FSP1) is observed in various types of human glomerulonephritis. Considering that FSP1 is secreted extracellularly and has been shown to have multiple biological effects on distant cells, we postulated that secreted FSP1 from podocytes might impact renal tubules. Our RNA microarray analysis in a tubular epithelial cell line (mProx) revealed that FSP1 induced the expression of heme oxygenase 1, sequestosome 1, solute carrier family 7, member 11, and cystathionine gamma-lyase, all of which are associated with nuclear factor erythroid 2-related factor (Nrf2) activation. Therefore, FSP1 is likely to exert cytoprotective effects through Nrf2-induced antioxidant activity. Moreover, in mProx, FSP1 facilitated Nrf2 translocation to the nucleus, increased levels of reduced glutathione, inhibited the production of reactive oxygen species (ROS), and reduced cisplatin-induced cell death. FSP1 also ameliorated acute tubular injury in mice with cisplatin nephrotoxicity, which is a representative model of ROS-mediated tissue injury. Similarly, in transgenic mice that express FSP1 specifically in podocytes, tubular injury associated with cisplatin nephrotoxicity was also mitigated. Extracellular FSP1 secreted from podocytes acts on downstream tubular cells, exerting renoprotective effects through Nrf2-mediated antioxidant activity. Consequently, podocytes and tubular epithelial cells have a remote communication network to limit injury.

Btg2 Promotes Focal Segmental Glomerulosclerosis via Smad3-Dependent Podocyte-Mesenchymal Transition

Podocyte injury plays a critical role in the progression of focal segmental glomerulosclerosis (FSGS). Here, it is reported that B-cell translocation gene 2 (Btg2) promotes Adriamycin (ADR)-induced FSGS via Smad3-dependent podocyte-mesenchymal transition. It is found that in FSGS patients and animal models, Btg2 is markedly upregulated by podocytes and correlated with progressive renal injury. Podocyte-specific deletion of Btg2 protected against the onset of proteinuria and glomerulosclerosis in ADR-treated mice along with inhibition of EMT markers such as α-SMA and vimentin while restoring epithelial marker E-cadherin. In cultured MPC5 podocytes, overexpression of Btg2 largely promoted ADR and TGF-β1-induced EMT and fibrosis, which is further enhanced by overexpressing Btg2 but blocked by disrupting Btg2. Mechanistically, Btg2 is rapidly induced by TGF-β1 and then bound Smad3 but not Smad2 to promote Smad3 signaling and podocyte EMT, which is again exacerbated by overexpressing Btg2 but blocked by deleting Btg2 in MPC5 podocytes. Interestingly, blockade of Smad3 signaling with a Smad3 inhibitor SIS3 is also capable of inhibiting Btg2 expression and Btg2-mediated podocyte EMT, revealing a TGF-β/Smad3-Btg2 circuit mechanism in Btg2-mediated podocyte injury in FSGS. In conclusion, Btg2 is pathogenic in FSGS and promotes podocyte injury via a Smad3-dependent EMT pathway.