A possible contribution of lipocalin-2 to the development of dermal fibrosis, pulmonary vascular involvement and renal dysfunction in systemic sclerosis

BACKGROUND

Lipocalin-2 is an adipocytokine implicated in apoptosis, innate immunity, angiogenesis, and the development of chronic kidney disease.

OBJECTIVES

To investigate the role of lipocalin-2 in systemic sclerosis (SSc).

MATERIALS AND METHODS

Serum lipocalin-2 levels were determined by enzyme-linked immunosorbent assay in 50 patients with SSc and 19 healthy subjects. Lipocalin-2 expression was evaluated in the skin of patients with SSc and bleomycin (BLM)-treated mice and in Fli1-deficient endothelial cells by reverse transcriptase-real time polymerase chain reaction, immunoblotting and/or immunohistochemistry.

RESULTS

Although serum lipocalin-2 levels were comparable between patients with SSc and healthy controls, the prevalence of scleroderma renal crisis was significantly higher in patients with SSc with elevated serum lipocalin-2 levels than in those with normal levels. Furthermore, serum lipocalin-2 levels inversely correlated with estimated glomerular filtration rate in patients with SSc with renal dysfunction. Among patients with SSc with normal renal function, serum lipocalin-2 levels positively correlated with skin score in patients with diffuse cutaneous SSc with disease duration of < 3 years and inversely correlated with estimated right ventricular systolic pressure in total patients with SSc. Importantly, in SSc lesional skin, lipocalin-2 expression was increased in dermal fibroblasts and endothelial cells. In BLM-treated mice, lipocalin-2 was highly expressed in dermal fibroblasts, but not in endothelial cells. On the other hand, the deficiency of transcription factor Fli1, which is implicated in SSc vasculopathy, induced lipocalin-2 expression in cultivated endothelial cells.

CONCLUSIONS

Lipocalin-2 may be involved in renal dysfunction and dermal fibrosis of SSc. Dysregulated matrix metalloproteinase-9/lipocalin-2-dependent angiogenesis due to Fli1 deficiency may contribute to the development of pulmonary arterial hypertension associated with SSc.

Constitutive activation of c-Abl/protein kinase C-δ/Fli1 pathway in dermal fibroblasts derived from patients with localized scleroderma

BACKGROUND

A noncanonical pathway of transforming growth factor-β signalling, the c-Abl/protein kinase C-δ (PKC-δ)/Friend leukemia virus integration 1 (Fli1) axis, is a powerful regulator of collagen synthesis in dermal fibroblasts.

OBJECTIVES

To investigate the significance of the c-Abl/PKC-δ/Fli1 pathway for the establishment of the profibrotic phenotype in lesional dermal fibroblasts from patients with localized scleroderma (LSc).

METHODS

The activation status of the c-Abl/PKC-δ/Fli1 pathway was evaluated by immunoblotting and chromatin immunoprecipitation using cultured dermal fibroblasts from patients with LSc and closely matched healthy controls and by immunostaining on skin sections. The effects of a platelet-derived growth factor receptor inhibitor AG1296 and gene silencing of c-Abl on the expression levels of type I collagen were evaluated by immunoblotting.

RESULTS

The phosphorylation levels of Fli1 at threonine 312 were increased, while the total Fli1 levels and the binding of Fli1 to the COL1A2 promoter were decreased, in cultured LSc fibroblasts compared with cultured normal fibroblasts. Furthermore, in cultured LSc fibroblasts, the expression levels of c-Abl were elevated compared with cultured normal fibroblasts and PKC-δ was preferentially localized in the nucleus. These findings were also confirmed in vivo by immunohistochemistry using skin sections. Moreover, gene silencing of c-Abl, but not AG1296, significantly suppressed the expression of type I collagen in cultured LSc fibroblasts.

CONCLUSIONS

Constitutive activation of the c-Abl/PKC-δ/Fli1 pathway at least partially contributes to the establishment of the profibrotic phenotype in LSc dermal fibroblasts, which provides a novel molecular basis to explain the efficacy of imatinib against skin sclerosis in a certain subset of LSc.

Augmented production of soluble CD93 in patients with systemic sclerosis and clinical association with severity of skin sclerosis

BACKGROUND

The cell surface protein CD93, expressed on endothelial and myeloid cells, mediates phagocytosis, inflammation and cell adhesion. A soluble form of CD93 (sCD93) is released during inflammation.

OBJECTIVES

To determine the serum sCD93 level and its association with clinical parameters in patients with systemic sclerosis (SSc).

METHODS

Serum sCD93 levels were examined by enzyme-linked immunosorbent assay in 59 patients with SSc, 24 patients with systemic lupus erythematosus and 47 healthy individuals. The expression of CD93 in skin tissues was examined immunohistochemically. In a retrospective longitudinal study, sera from 11 patients with SSc were analysed.

RESULTS

Serum sCD93 levels were increased in patients with SSc compared with healthy individuals (P<0·001). Patients with diffuse cutaneous SSc showed greater levels of sCD93 than those with limited cutaneous SSc (P<0·01) or systemic lupus erythematosus (P<0·01). Serum sCD93 levels correlated positively with the severity of skin sclerosis. Strong CD93 immunostaining was observed on endothelial cells in lesional skin tissues. In the longitudinal study, sCD93 levels decreased in parallel with improvement in skin sclerosis.

CONCLUSIONS

Serum sCD93 levels are increased in patients with SSc and correlate with the severity and activity of skin sclerosis. CD93 may contribute to the development of skin fibrosis in SSc.

Clinical significance of serum retinol binding protein-4 levels in patients with systemic sclerosis

BACKGROUND

Retinol binding protein-4 (RBP-4) is a member of adipocytokines, which is potentially associated with fibrosis, vasodilation, and angiogenesis in addition to insulin resistance.

OBJECTIVE

To investigate the clinical significance of serum RBP4 levels in patients with systemic sclerosis (SSc), which is a systemic autoimmune disease characterized by fibrosis and vasculopathy.

METHODS

Serum RBP4 levels were determined by enzyme-linked immunosorbent assay in 62 SSc patients and 19 healthy controls.

RESULTS

Similar to patients with chronic kidney disease, serum RBP4 levels inversely correlated with estimated glomerular filtration rate in SSc patients with renal dysfunction. Therefore, analyses were carried out by excluding SSc patients with estimated glomerular filtration rate <60 mL/min/1.73 m(2) . Serum RBP4 levels were significantly lower in diffuse cutaneous SSc (dcSSc) than in control subjects [median (25-75 percentile); 25.8 μg/mL (19.6-47.0) vs. 43.1 μg/mL (31.7-53.4), P < 0.05], while there was no significant difference between limited cutaneous SSc (lcSSc) [28.0 μg/mL (25.4-43.3)] and control subjects. In both of dcSSc and lcSSc, patients with Raynaud's phenomenon had RBP4 levels significantly lower than those without. Furthermore, serum RBP4 levels inversely correlated with pulmonary function test results in dcSSc and with right ventricular systolic pressure in lcSSc. CONCLUSION  Decreased RBP4 levels are associated with the prevalence of Raynaud's phenomenon in dcSSc and lcSSc, with the severity of interstitial lung disease in dcSSc, and with the degree of pulmonary vascular involvement in lcSSc, suggesting the possible contribution of RBP4 to the pathological events in this disorder.

Effects of bosentan on nondigital ulcers in patients with systemic sclerosis

BACKGROUND

Bosentan is an oral dual endothelin receptor antagonist, which has been shown to be efficacious for preventing new digital ulcers in patients with systemic sclerosis (SSc) in two high-quality randomized controlled trials. However, its efficacy for nondigital ulcers in SSc remains unknown.

OBJECTIVES

To evaluate the efficacy of bosentan on nondigital ulcers in patients with SSc.

METHODS

Bosentan was administered to five patients with SSc with pulmonary arterial hypertension, who also had nondigital ulcers refractory to conventional treatments. The efficacy of bosentan on nondigital ulcers and its association with clinical features of ulcers were analysed.

RESULTS

The nondigital ulcers refractory to conventional treatments were significantly improved by the administration of bosentan in cases surrounded with severe cyanosis. In contrast, nondigital ulcers without cyanosis were still refractory to bosentan therapy.

CONCLUSIONS

Bosentan may be efficacious for accelerating the healing of nondigital ulcers with severe cyanosis, suggesting that nondigital ulcers caused by severely impaired peripheral circulation are highly responsive to this treatment.

Serum apelin levels: clinical association with vascular involvements in patients with systemic sclerosis

BACKGROUND

Apelin is a bioactive peptide exerting its pro-angiogenic and pro-fibrotic effects in a context-dependent manner through the activation of its receptor APJ, which is ubiquitously expressed on the surface of various cell types. The activation of apelin/APJ signalling appears to be involved in the pathological process of fibrotic disorders, including liver cirrhosis.

OBJECTIVE

As an initial step to clarify the role of apelin/APJ signalling in the pathogenesis of systemic sclerosis (SSc), we investigated serum apelin levels and their clinical association in patients with SSc.

METHODS

Serum apelin levels were determined by a specific enzyme-linked immunosorbent assay in 56 SSc patients and 18 healthy controls.

RESULTS

Serum apelin levels were comparable among three groups, including diffuse cutaneous SSc, limited cutaneous SSc and control subjects (1.77 ± 1.48, 1.63 ± 1.51 and 1.61 ± 0.44 ng/mL, respectively). When we classified SSc patients into three groups according to disease duration, serum apelin levels were elevated in early SSc (<3 years) compared with mid-stage SSc (3-10 years) (1.74 ± 1.26 vs. 1.02 ± 0.52 ng/mL, P < 0.05). Importantly, in late stage SSc (>10 years), the prevalence of severe vascular involvements, including intractable skin ulcers, scleroderma renal crisis and pulmonary arterial hypertension, was significantly higher in patients with elevated serum apelin levels than in those without (100% vs. 20%, P < 0.05).

CONCLUSION

Apelin may be associated with altered and activated angiogenesis prior to fibrotic responses in early SSc and with the development of proliferative vasculopathy in late stage SSc.