Certainties and uncertainties concerning the contribution of pericytes to the pathogenesis of systemic sclerosis

Transcriptomic characterization of lung pericytes in systemic sclerosis-associated pulmonary fibrosis

Systemic sclerosis (SSc) is a chronic disease characterized by fibrosis and vascular abnormalities in the skin and internal organs, including the lung. SSc-associated pulmonary fibrosis (SSc-PF) is the leading cause of death in SSc patients. Pericytes are key regulators of vascular integrity and endothelial function. The role that pericytes play in SSc-PF remains unclear. We compared the transcriptome of pericytes from SSc-PF lungs (SScL) to pericytes from normal lungs (NORML). We identified 1,179 differentially expressed genes in SScL pericytes. Pathways enriched in SScL pericytes included prostaglandin, PI3K-AKT, calcium, and vascular remodeling signaling. Decreased cyclic AMP production and altered phosphorylation of AKT in response to prostaglandin E2 in SScL pericytes demonstrate the functional consequence of changes in the prostaglandin pathway that may contribute to fibrosis. The transcriptomic signature of SSc lung pericytes suggests that they promote vascular dysfunction and contribute to the loss of protection against lung inflammation and fibrosis.

The Pathogenesis of Systemic Sclerosis: The Origin of Fibrosis and Interlink with Vasculopathy and Autoimmunity

Systemic sclerosis (SSc) is an autoimmune disease associated with increased mortality and poor morbidity, impairing the quality of life in patients. Whilst we know that SSc affects multiple organs via vasculopathy, inflammation, and fibrosis, its exact pathophysiology remains elusive. Microvascular injury and vasculopathy are the initial pathological features of the disease. Clinically, the vasculopathy in SSc is manifested as Raynaud's phenomenon (reversible vasospasm in reaction to the cold or emotional stress) and digital ulcers due to ischemic injury. There are several reports that medications for vasculopathy, such as bosentan and soluble guanylate cyclase (sGC) modulators, improve not only vasculopathy but also dermal fibrosis, suggesting that vasculopathy is important in SSc. Although vasculopathy is an important initial step of the pathogenesis for SSc, it is still unclear how vasculopathy is related to inflammation and fibrosis. In this review, we focused on the clinical evidence for vasculopathy, the major cellular players for the pathogenesis, including pericytes, adipocytes, endothelial cells (ECs), and myofibroblasts, and their signaling pathway to elucidate the relationship among vasculopathy, inflammation, and fibrosis in SSc.

A positive loop formed by SOX11 and periostin upregulates TGF-β signals leading to skin fibrosis

Systemic sclerosis (SSc) is a chronic, heterogenous disease of connective tissue characterized by organ fibrosis together with vascular injury and autoimmunity. Transforming growth factor (TGF)-β plays a central role in generating fibrosis, including SSc. Periostin is a matricellular protein playing a key role in the generation of fibrosis by amplifying the TGF-β signals. SOX (SRY-related HMG box) 11 is a transcription factor playing several important roles in organ development in embryos. We have previously shown that SOX11 induces periostin expression. However, the roles of the interactions among the TGF-β signals, periostin, and SOX11 remain unknown in the pathogenesis of SSc. In this study, we found that most clones of dermal fibroblasts derived from SSc patients showed constitutive, high expression of SOX11, which is significantly induced by TGF-β1. SOX11 forms a positive loop with periostin to activate the TGF-β signals in SSc dermal fibroblasts. Genetic deletion of Sox11 in Postn-expressing fibroblasts impairs dermal fibrosis by bleomycin. Moreover, using the DNA microarray method, we identified several fibrotic factors dependent on the TGF-β/SOX11/periostin pathway in SSc dermal fibroblasts. Our findings, taken together, show that a positive loop formed by SOX11 and periostin in fibroblasts upregulates the TGF-β signals, leading to skin fibrosis.

The rationale for targeting the JAK/STAT pathway in scleroderma-associated interstitial lung disease

The etiopathogenesis of systemic sclerosis (SSc)-associated interstitial lung disease (ILD) is still debated and no therapeutic options have proved fully effective to date. The intracellular Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is highly conserved among either immune or nonimmune cells and involved in inflammation and fibrosis. Evidence from preclinical studies shows that the JAK/STAT signaling cascade has a crucial role in the differentiation of autoreactive cells as well as in the extracellular matrix remodeling that occurs in SSc. Therefore, it is likely that the use of oral small molecule JAK-inhibitors, especially if prescribed early, may prevent or slow the progression of SSc-associated ILD, but few clinical studies currently support this hypothesis.

The contribution of HERV-E clone 4-1 and other HERV-E members to the pathogenesis of rheumatic autoimmune diseases

Human endogenous retroviruses (HERV)-E consist of a family of more than 1300 elements, stably integrated in the human genome. Some of them are full-length proviruses able to synthesize the viral proteins gag, pol and env. The reactivation of HERV-E elements has been associated to placentation, cancer and autoimmunity. In this narrative review, we aimed to report the status of the art concerning the involvement of HERV-E in rheumatic autoimmune diseases. Following a research on PubMed database, a total of 87 articles were selected. The highest amount of evidence derives from studies on systemic lupus erythematosus (SLE), whereas a few to no data are available on other immune-mediated diseases. In SLE, the hyper-expression of HERV-E clone 4-1 in peripheral blood mononuclear cells or differentiated lymphocytes has been associated with disease activity and autoantibody production. It is likely that HERV-E take part to the pathogenesis of rheumatic autoimmune diseases but additional research is needed.