Increased circulating levels of tissue kallikrein in systemic sclerosis correlate with microvascular involvement

Similarities between COVID-19 and systemic sclerosis early vasculopathy: A "viral" challenge for future research in scleroderma

OBJECTIVE

To review similarities between COVID-19 and systemic sclerosis (SSc) early vasculopathy to provide novel insights into both diseases.

METHODS

A narrative review of the literature supplemented with expert opinion.

RESULTS

There is clear evidence that the endothelium is at the centre stage in SSc and COVID-19, with endothelial cell activation/injury and dysfunction creating the crucial evolving step in the pathogenesis of both diseases. The angiotensin system has also been implicated in the early stages of both COVID-19 and SSc. Autoptic studies provide novel insights into the effects of SARS-CoV-2 on the endothelium. Normal endothelium and endothelial dysfunction in COVID-19 and SSc are discussed. It is debated whether SARS-CoV-2 infection triggers autoimmunity with production of autoantibodies which is of mechanistic interest because other viral illnesses are potentially involved in endothelial dysfunction and in SSc pathogenesis.

CONCLUSION

COVID-19 is due to a direct assault of SARS-CoV-2 on the vascular system as an acute infection, whereas SSc remains a chronic/sub-acute autoimmune disease of largely unknown etiology Further study and exploration of the SARS-CoV-2 pathogenic mechanisms might provide further useful milestones in the understanding of the early SSc pathogenesis.

Vascular biomarkers and correlation with peripheral vasculopathy in systemic sclerosis

Vascular disease is a hallmark of systemic sclerosis (SSc). It is present in every patient, being responsible both for the earliest clinical manifestations and the major life-threatening complications of the disease, and thus determining important morbidity and mortality. In SSc, progressive vascular injury leads to vascular tone dysfunction and reduced capillary blood flow, with consequent tissue ischemia and chronic hypoxia. These phenomena are often accompanied by abnormal levels of vascular factors. Microangiopathy in SSc may be easily assessed by nailfold videocapillaroscopy. The variety of derangements detected in the nailfold capillaries is accompanied by abnormal levels of different vascular mediators and appears to be the best evaluable predictor of the development of peripheral vascular complications, such as digital ulcers. The purpose of this review is to summarize in SSc the most relevant vascular biomarkers and the main associations between vascular biomarkers and capillaroscopic parameters and/or the presence of digital ulcers. Vascular biomarkers could become useful predictive factors of vascular damage in SSc, allowing an earlier management of vascular complications.

Transforming growth factor β--at the centre of systemic sclerosis

Transforming growth factor β (TGF-β) has long been implicated in fibrotic diseases, including the multisystem fibrotic disease systemic sclerosis (SSc). Expression of TGF-β-regulated genes in fibrotic skin and lungs of patients with SSc correlates with disease activity, which points to this cytokine as the central mediator of pathogenesis. Patients with SSc often develop pulmonary arterial hypertension (PAH), a particularly lethal complication caused by vascular dysfunction. Several genetic diseases with vascular features related to SSc, such as familial PAH and hereditary haemorrhagic telangiectasia, are caused by mutations in the TGF-β-sensing ALK-1 signalling pathway. These observations suggest that increased TGF-β signalling causes both vascular and fibrotic features of SSc. The question of how latent TGF-β becomes activated in local SSc tissues is, therefore, central to the understanding of SSc. Both TGF-β1 and TGF-β3 can be activated by integrins αvβ6 and αvβ8, whose upregulation in bronchial epithelial cells can activate TGF-β in SSc lungs. Other αv integrins, thrombospondin-1 or altered TGF-β sequestration by matrix proteins might be important in other target tissues. How the immune system triggers this process remains unclear, although links between inflammation and TGF-β activation are emerging. Together, these observations provide an increasingly secure framework for understanding TGF-β in SSc pathogenesis.

A systematic overview on the use and relevance of capillaroscopy in systemic sclerosis

Capillaroscopy is a non-invasive and safe technique that allows the detection and quantification of the early microvascular abnormalities that characterize secondary Raynaud's phenomenon. The well-established role of capillaroscopy for the early diagnosis of systemic sclerosis, its inclusion in the classification criteria, combined with its predictive value for clinical complications of the disease and its potential for monitoring disease progression and treatment response, makes nailfold capillaroscopy an important assessment in clinical practice and research. Capillaroscopy provides a unique window into the microcirculation and its application in diseases in which a microvascular component is suspected; it also may provide new insights into their pathophysiology and natural history.

Mechanisms in the loss of capillaries in systemic sclerosis: angiogenesis versus vasculogenesis

Systemic sclerosis (SSc, scleroderma) is a chronic, multisystem connective tissue disorder affecting the skin and various internal organs. Although the disease is characterized by a triad of widespread microangiopathy, fibrosis and autoimmunity, increasing evidence indicates that vascular damage is a primary event in the pathogenesis of SSc. The progressive vascular injury includes persistent endothelial cell activation/damage and apoptosis, intimal thickening, delamination, vessel narrowing and obliteration. These profound vascular changes lead to vascular tone dysfunction and reduced capillary blood flow, with consequent tissue ischemia and severe clinical manifestations, such as digital ulceration or amputation, pulmonary arterial hypertension and scleroderma renal crisis. The resulting tissue hypoxia induces complex cellular and molecular mechanisms in the attempt to recover endothelial cell function and tissue perfusion. Nevertheless, in SSc patients there is no evidence of significant angiogenesis and the disease evolves towards chronic tissue ischemia, with progressive and irreversible structural changes in multiple vascular beds culminating in the loss of capillaries. A severe imbalance between pro-angiogenic and angiostatic factors may also lead to impaired angiogenic response during SSc. Besides insufficient angiogenesis, defective vasculogenesis with altered numbers and functional defects of bone marrow-derived endothelial progenitor cells may contribute to the vascular pathogenesis of SSc. The purpose of this article is to review the contribution of recent studies to the understanding of the complex mechanisms of impaired vascular repair in SSc. Indeed, understanding the pathophysiology of SSc-associated vascular disease may be the key in dissecting the disease pathogenesis and developing novel therapies. Either angiogenic or vasculogenic mechanisms may potentially become in the future the target of therapeutic strategies to promote capillary regeneration in SSc.

Vascular disease in scleroderma: angiogenesis and vascular repair

Vascular abnormalities are one of the primary pathologic components of scleroderma. An early vascular indicator is aberrant nail fold capillaries that appear to undergo a switch from a pro- to anti-angiogenic process. Later in the disease process, ineffective and aberrant wound healing becomes apparent with frequent and widespread fibrosis. Pulmonary hypertension, largely due to the loss of pulmonary arterial vasculature, is frequently observed in late stages of the disease. The common theme of all these processes is abnormal regeneration of the vasculature and ongoing vascular losses due to defective maintenance of the vasculature. Although most aspects of vascular injury in scleroderma are poorly understood, certain biologic themes are beginning to emerge that are important in understanding scleroderma-related vascular disease.

Current concepts in normal and defective angiogenesis: implications for systemic sclerosis

Vascular abnormalities are a major component of systemic sclerosis, but little is known about the events or mechanisms that initiate vascular injury and prevent its repair. Early stages of systemic sclerosis are characterized by an exaggerated angiogenic response later replaced by defective wound healing and fibrosis. In this review, we summarize the current knowledge of the angiogenic imbalance in systemic sclerosis.

Prognostic markers for systemic sclerosis

The prognosis of systemic sclerosis depends chiefly on the extent of the skin lesions, which correlates with the severity of the cardiovascular, pulmonary, and renal manifestations. An erythrocyte sedimentation rate greater than 15-25 mm/h or a hemoglobin level lower than 12.5-11 g/dl is associated with a 2.5- to 3-fold increase in mortality. Anticentromere antibodies are associated with delayed pulmonary hypertension, anti-topoisomerase I antibodies (Scl 70) with interstitial lung disease, and anti-RNA polymerase III antibodies with renovascular hypertension. The risk of death is directly related to the autoantibody pattern. For instance, in a study of 1432 cases from the Pittsburgh Scleroderma Databank, 10-year survival among patients with limited cutaneous disease was 88% in the group with anti-U1-RNP, 75% in the group with anticentromere antibodies, 72% in the group with anti-PmScl, and 65% in the group with anti-Th/To. Ten-year survival in patients with diffuse cutaneous disease was 64% with anti-topoisomerase antibodies, 61% with anti-U3-RNP, and 75% with anti-RNA polymerase III. Several prognostic markers are also available for predicting the risk of organ involvement. For instance, serum levels of KL-6, surfactant proteins SP-A and SP-D, the collagen peptide PIIINP, and homocysteine are associated with the risk of fibrosing alveolitis. Serum levels of CD40L and NP-ProBNP, circulating endothelial cells, and serum anticardiolipin titers correlate with the risk of arterial hypertension. Serum VCAM1 and markers for oxidative stress such as carboxyl terminus residues predict the risk of vascular disease. Other serum markers for organ involvement are under study, although their predictive performance remains to be evaluated.