Background/Purpose: Scleroderma-associated Interstitial Lung Disease (SSc-ILD) is more prevalent and more severe in African Americans (AA) than in Caucasian (C) patients, but little is known of the factors underlying this health disparity.  In the course of studies comparing caveolin-1 function in SSc and healthy blood monocytes, we made the striking observation that healthy AA monocytes share abnormalities with SSc monocytes including low caveolin-1 levels. The aim of this study was to determine the consequences of low caveolin-1 expression in AA and SSc monocytes,

Methods: The study was approved by the university’s IRB for Human Subject Research. Monocytes were isolated from the blood of SSc-ILD patients and healthy donors using negative selection.  SSc patients fulfilled the ACR criteria for the classification of systemic sclerosis. Monocyte migration was assayed in Multiwell Chemotaxis Chambers, with or without treatment with caveolin-1 scaffolding domain (CSD) peptide and control peptides. CD14, CXCR4, alpha-smooth muscle actin (ASMA), and caveolin-1 levels were determined by Western blot analysis and immunostaining. For fibrocyte differentiation, peripheral blood mononuclear cells (PBMC) isolated from 40 ml of blood were incubated for 14 days in 20 ml DMEM/ 20 % FBS on fibronectin-coated plates with or without treatment with CSD.

Results: Like SSc-ILD monocytes, healthy AA monocytes differ from healthy C monocytes in signaling and in function.  Healthy AA monocytes contained only 49 % as much caveolin-1 as healthy C monocytes (n = 7).  The percentage of AA monocytes that migrated in response to the CXCR-4 ligand, CXCL12, was almost three-fold enhanced (19 ± 2.5 vs 57 ± 4.3) compared to C monocytes (n = 10). Like SSc monocytes, when healthy AA monocytes were treated with CSD to restore caveolin-1 function, migration in response to CXCL12 was inhibited by at least 70%.  When we compared the ability of healthy C monocytes, healthy AA monocytes, and SSc monocytes to differentiate into fibrocytes, we observed a three-fold increase (quantified in terms of number of spindle-shaped cells per high-power field) in both the SSc and healthy AA samples compared to the healthy C samples (C = 6.4 ± 2.1, AA = 17.3 ± 3.8, SSc = 16.5 ± 4.0; n = 12).  In all three cell types, CSD treatment inhibited fibrocyte differentiation by >50%.  Although fibrocyte differentiation is enhanced in both healthy AA and SSc, there are phenotypic differences between these two groups.  When the CD14- population is isolated by FACS from each source, then cultured on fibronectin-coated coverslips, the level of collagen I and caveolin-1 is similar for all three groups, CXCR4 was upregulated in both the AA and SSc fibrocytes, and ASMA was upregulated only in the SSc fibrocytes.

Conclusion: Our results support the notion that low caveolin-1 levels may play a role in the predisposition of the AA population to SSc-ILD through effects both on the migration of fibrocytes and fibrocyte precursors into damaged tissue and on fibrocyte differentiation.

 

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/caveolin-1-deficiency-may-play-a-role-in-the-predisposition-of-african-americans-to-ssc-ild/