Background/Purpose:

Transplacental passage of maternal autoantibodies (Ab) reactive with the SSA/Ro-SSB/La ribonucleoprotein complex is associated with the development of cardiac injury in the fetus passively exposed to these Ab. However, antibodies are necessary but insufficient to cause disease, and the final pathway to this rapid fibrosis may be variable: kept totally in check in most fetuses (normal sinus rhythm), subclinical in others (first-degree block), and fully executed in very few (advanced block, fibrosis and macrophage infiltration).  This study was initiated to evaluate a novel profibrosing candidate, MEK5/ERK5 of the mitogen activated protein kinase (MAPK) pathway, which in the context of anti-Ro antibodies may prime fetal cardiac fibroblasts toward an irreversible scarring phenotype characteristic of heart block. 

Methods:

Primary human fetal cardiac fibroblasts were treated with secreted products generated from activated macrophages (an in vitro model of heart block) or TGFβ in the presence and absence of BIX 02189 (10uM), a specific MEK5/ERK5 inhibitor. The phenotype was evaluated by the profile of profibrotic genes including ACTA2, MMP-13, and PAI-1 (qRT-PCR), and expression of α-smooth muscle actin (α-SMA, indirect immunofluorescence).

Results:

Treatment of human fetal cardiac fibroblasts with supernatants from macrophages transfected with hY3, an ssRNA associated with Ro60 (surrogate for immune complexes), induced the expression of the myofibroblast marker α-SMA, which was inhibited by co-treatment with BIX 02189 (immunofluorescence, N=3).  As expected, macrophage supernatants increased fetal fibroblast mRNA expression of ACTA2, the gene encoding α-SMA, by 4-fold (24 hr), which was completely attenuated by co-treatment with BIX 02189. In parallel conditions, other profibrosing biomarkers, including MMP-13 and PAI-1 transcripts, were similarly upregulated and subsequently inhibited by BIX 02189 (MMP-13: 15.91 vs. 3.06, respectively; PAI-1: 2.27±0.1 vs. 0.84±0.1, respectively, p=0.01, N=3). Since previous work has shown that supernatants from macrophages incubated with anti-Ro immune complexes induced the fibroblast secretion of TGFβ, this cytokine was evaluated as a comparison to the fibrotic “potency” of the macrophage supernatants. TGFβ showed a similar yet less marked upregulation of the profibrotic genes MMP-13 and PAI-1, which was significantly inhibited by co-treatment with BIX 02189.

Conclusion:  

These data identify the MEK5/ERK5 pathway in fetal cardiac fibroblasts as a novel and coverable target to forestall the progression of cardiac injury toward irreversible fibrosis induced by anti-Ro immune complex activated macrophages.

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/mek5erk5-a-lynchpin-of-human-cardiac-fibroblast-transdifferentiation-to-a-scarring-phenotype-in-autoimmune-congenital-heart-block/