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. We reported recently that healthy AA monocytes share abnormalities with SSc ILD monocytes including low caveolin-1 levels and hypermigration towards chemokine SDF-1 due to upregulation of its receptor CXCR4. In the current study we have investigated other chemokine receptors that are involved in SSc ILD, namely CCR1, CCR2, and CCR3.  The aim of this study was to determine whether these receptors are also overexpressed in SSc ILD and healthy AA monocytes and the functional consequences of their overexpression.

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 by negative selection.  SSc ILD patients fulfilled the ACR criteria for the classification of systemic sclerosis. Monocyte migration was assayed in Multiwell Chemotaxis Chambers using cells treated with the caveolin-1 scaffolding domain (CSD) peptide or control peptide. CCR1, CCR2, CCR3, ERK, pERK, Src, pSrc, Lyn, pLyn, and caveolin-1 levels were determined by Western blotting and immunostaining.

Results:

In the current study, we observed that the expression of CCR1, CCR2, and CCR3 is enhanced in SSc ILD monocytes and healthy AA monocytes compared to healthy C monocytes.  In accord with these findings, compared to healthy C monocytes, the migration of healthy AA monocytes toward the CCR2 ligand MCP-1 was enhanced two-fold (p < 0.05) and toward the common CCR1,2,3 ligand MCP-3 was also enhanced two-fold (p < 0.05).  SSc ILD monocyte migration (compared to C monocyte migration) toward MCP-1 was enhanced 10-fold (p < 0.001) and toward MCP-3 was enhanced 5-fold (p < 0.001).  In all cases, treatment with CSD inhibited migration > 50 %, demonstrating that the enhanced migration of SSc ILD and healthy AA monocytes is due to their relative lack of caveolin-1.  To study signaling downstream from CCR1, CCR2, and CCR3; healthy C, healthy AA, and SSc ILD patient monocytes were treated with MCP-1.  Baseline activation of ERK and Src was two-fold increased in AA compared to C while Lyn activation was similar in C and AA.  All three kinases were greatly enhanced in SSc ILD.  MCP-1 activated ERK in both C and AA monocytes, but had no effect on Src and Lyn.  MCP-1 did not increase the already high level of ERK activation in SSc ILD monocytes, but did further increase the already high levels of Src and Lyn activation.  In contrast, MCP-3 appears to inhibit ERK, Src, and Lyn in all three groups; suggesting that MCP-1 and MCP-3 signaling during cell migration occur through distinct mechanism.  The relevance of these observations to human disease was demonstrated in immunostaining experiments showing that CCR1, CCR2, CCR3, MCP-1, and MCP-3 are all overexpressed in SSc ILD lung tissue compared to control healthy lung tissue. 

Conclusion: Low caveolin-1 levels may play a role in the predisposition of the AA population to SSc ILD via the regulation of the expression of chemokine receptors CCR1, CCR2, and CCR3 in monocytes and through the activation of ERK, Src, and Lyn.

---

« Back to 2013 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/enhanced-expression-of-ccr-receptors-in-healthy-aa-and-ssc-ild-monocytes/