Anti-vinculin antibodies as a novel biomarker in Egyptian patients with systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune disorder characterized by skin and multiple organ involvement; its underlying pathophysiologic mechanisms often include vasculopathy, autoimmunity, and fibrosis [1]. There is evidence that several stages occur prior to the onset of autoimmune disorders. Based on autoantibody findings [2] and predictive models [3], a thorough examination of these stages may lead to prophylaxis in the first instance, slowing or halting the onset of disease in the future, implying that an increase in autoantibody production contributes significantly to the clinical symptoms of many autoimmune disorders [4]. Autoantibodies in SSc have been shown to predict the clinical phenotype [5]. Vascular involvement, including PAH, has been associated with SSc. In addition, it impacts SSc pathogenesis, and endothelial cell activation may alter phenotypic presentation. Endothelial vinculin promotes angiogenesis [1]. In comparison to healthy control sera, Villano et al. found that SSc sera increased vinculin expression in endothelial cells [6] Endothelial vinculin expression and assembly must be regulated during angiogenesis [7, 8, 9].

Hence, disturbed vinculin expression may aggravate SSc’s already-defective angiogenic mechanisms [10]. In addition, anti-endothelial cell antibodies targeting antigens such as vinculin have been detected in SSc patients with and without PAH [11]. Vinculin overexpression in SSc may produce anti-vinculin antibodies, which may cause vasculopathic symptoms. According to Suliman and colleagues, PAH was linked to a significant increase in anti-vinculin antibody levels [12].

Skin and lung fibrosis in scleroderma is a maladaptive repair mechanism [1]. Fibrosis is characterized by the replacement of normal tissue structure with collagen-rich connective tissue, resulting in a rigid structure [13]. Activated vascular, epithelial, and immune cells release profibrotic cytokines, chemokines, growth factors, lipid mediators, and autoantibodies. These antibodies are present in more than 90% of patients [1, 14].

Vinculin protein is an actin-binding protein expressed in high amounts in basal bronchial cells and low amounts in alveolar cells but is not detected in ciliated cells and goblet cells [10].

Vinculin is utilized to measure cell–cell and cell–ECM (focal adhesion) adherens-type junctions, although its function is unknown [9]. Cell migration is slowed when vinculin is overexpressed, whereas it is accelerated when vinculin is downregulated. Vinculin-deficient cells are less adherent, more motile, and have fewer and smaller focal adhesions [11].

Serum biomarkers for diagnosing and tracking SSc-related lung involvement are sparse, particularly those that can identify early pulmonary interstitial fibrosis. Therefore, identifying high-risk groups for PIF remains difficult.

Scleroderma patients’ vulnerability to IPF has not been studied using serum antibodies to the vinculin protein. Serum biomarkers for diagnosing and tracking SSc-related lung involvement are sparse, especially those that can identify early pulmonary interstitial fibrosis. Still, there are concerns about identifying high-risk groups for PIF.

Scleroderma patients’ susceptibility to IPF has not been studied using serum antibodies to the vinculin protein. The current study focuses on [1] determining whether anti-vinculin autoantibodies provide insight into a diagnosis of SSc and [2] comparing serum anti-vinculin antibody levels in two SSc patient groups, namely, PAH-predominant and IPF-predominant groups.

The number of positive anti-vinculin Abs was substantially higher in SSc patients than in healthy controls in both groups (group I (PAH-predominant group) and group II (ILD-predominant group)), which is consistent with previous research findings [6] [12].

In ILD-predominant scleroderma cases, anti-vinculin positivity was associated with a higher proportion of CT nodular opacity and honeycombing and a lower proportion of CT ground-glass opacity. There were no other significant associations between anti-vinculin Abs and the parameters studied. Vinculin, a cytoskeletal protein, is expressed in the lungs. This protein promotes fibrosis by participating in cell–cell and cell–ECM adhesion [19]. Vinculin dysregulation may aggravate pulmonary fibrosis in SSc patients. We hypothesized that vinculin overexpression in SSc increased anti-vinculin Abs, contributing to interstitial lung fibrosis.

To our knowledge, this is the first study to investigate the use of anti-vinculin antibodies in scleroderma patients with ILD considering that our search of PubMed for studies was published in January 2022 using the following query ("Pulmonary Fibrosis"[Mesh]) AND "Scleroderma, Systemic"[Mesh]). Furthermore, "Vinculin"[Mesh] yielded no results. Hence, more research is needed to evaluate if anti-vinculin antibodies can be utilized to diagnose pulmonary fibrosis in SSc patients.

Our study showed that the PAH group showed significantly higher anti-vinculin antibody levels and positivity than the ILD group. This conclusion is consistent with Suliman et al.’s [12] suggestion that anti-vinculin was only related to PAH, highlighting the need to examine a broader sample to demonstrate this potential correlation [12].

Before vinculin antibody measurements can be used, disease-specific normal and abnormal values must be established. Based on the values of the patient and control groups, we discovered that 1.25 was the optimal cutoff for diagnosing SSc using patient populations and healthy controls, which is inconsistent with the findings of Pimentel et al. [20]. However, we assessed anti-vinculin antibodies in IBS patients, not scleroderma patients, and our optimum cutoff for SSc diagnosis is incompatible with Suliman et al. (OD of 1.68) [6] [12]. The variance in cutoff values can be attributed to sample size, ethnicity, location, test chemicals, and measurement instruments.

Our research has a wide range of implications. First, our findings suggest that in SSc, vinculin protein may play a role in the pathogenesis of the vascular and fibrotic changes detected in the ECM and cell migration.

Based on the results of previous studies implicating vinculin as a potential target of anti-endothelial antibodies in SSc, it appears that vinculin may play an essential role in SSc pathophysiology when disrupted by an autoimmune process.

The current study’s strengths include the following: the appropriate selection of participants, the strict diagnosis of scleroderma following the ACR/EULAR 2013 SSc requirements, the inclusion of a control group for comparison, and the exclusion of patients with symptoms overlapping those of other connective tissue diseases. To our knowledge, ILD in scleroderma patients has never before been studied with anti-vinculin antibodies. Furthermore, this study could differentiate between PAH and IPF groups, two of the most common pathologies involved in SSc and have been linked to significant mortality.

However, it should be noted that the current study has some limitations. First, our sample may be representative of only the Egyptian population. There were two distinct SSc groups from one hospital. Consequently, our findings cannot be generalized.

Second, there is no agreement on the cutoff for normal and abnormal values in the diagnosis of SSc. More research in different geographic areas will be required to determine region-specific cutoffs for background antibody levels required to differentiate true disease from healthy individuals. In addition, further investigation is required to evaluate the difference in cutoff antibody levels between PAH and ILD subjects and the lower specificity for the cutoff differentiating PAH from ILD. Further research with a larger sample size will be needed to verify whether anti-vinculin cutoff levels can be used for the diagnosis of scleroderma and to differentiate between PAH and ILD.

The best cutoff value for a diagnostic test can be determined by considering the prevalence of the disease of interest in the study population and the costs (not just financial) of false-negative (FN) and false positive (FP) results [21].

Anti-vinculin antibodies may serve as biomarkers for scleroderma, allowing scleroderma to be an inclusion diagnosis rather than an exclusion diagnosis, and may aid in the targeting investigations in those who tested negative, given that not all scleroderma subjects test positive for this biomarker. In addition, anti-vinculin antibodies may provide new insights into the pathophysiology of some lung fibrotic changes, such as CT nodular opacity and honeycombing in ILD associated with scleroderma. The subsequent stage of our research involves investigating the potential mechanisms by which this biomarker contributes to the development of some lung fibrotic changes in subjects with ILD associated with scleroderma.