C0-C1f region of cardiac myosin binding protein-C induces pro-inflammatory responses in fibroblasts

Background

Cardiac myosin binding protein-C is a protein expressed in the myosin thick filament backbone that was recently described as a novel cardiac biomarker. Its N-terminal region, C0-C1f, is released within the first minutes of ischemia and plays a crucial role in the initiation of inflammation in bone marrow-derived macrophages. Long-term C0-C1f exposure induces cardiac fibrosis in transgenic mice; however, the mechanism by which C0-C1f causes fibrosis is unclear. The aim of the study was to investigate the effects of C0-C1f on fibroblasts, which are the main contributor to cardiac fibrosis, in vitro. We determined whether C0-C1f directly activates fibroblasts and causes a transdifferentiation to myofibroblasts or induces inflammatory responses. Moreover, we clarify whether other cell types could be involved in inducing fibrosis, i.e. by the release of pro-inflammatory cytokines upon C0-C1f interaction.

Methods

A novel human fibroblast cell line (huFib) was treated with C0-C1f, C0-Linker, TGF-β, or LPS for different time periods. Inflammatory and fibrotic responses were evaluated at the RNA and protein level using different techniques including microarray, qRT-PCR, and immunofluorescence imaging. For signalling pathway analysis, TLR4 and NFκB were inhibited using chemical compounds TAK-242 or Bay11–0785 respectively.

Results

C0-C1f treatment induced an increase in mRNA corresponding to pro-inflammatory genes in huFib cells (i.a. CXL1 upon 24 hours treatment: 29 fold, p<0.001 and CCL2 4-fold, p<0.001). The mRNA expression levels of pro-fibrotic genes such as ACTA2 or COL1A1, which were upregulated by TGF-β, were not reduced by C0-C1f (ACTA2 induced by TGF-β: 3,8 fold, p<0.001, co-stimulation with C0-C1f: 1,8 fold, p=0.11 compared to control; COL1A1 induced by TGF-β: 2,94 fold, p<0.001, co-stimulation with C0-C1f: 2.09 fold (p<0.01) compared to control. Interestingly, co-stimulation of fibroblasts with C0-C1f and TGF-β led also to markedly lower inflammatory response compared to C0-C1f treatment alone (CXCL1 induction upon co-stimulation: 2,0 fold, p<0.001, CCL2: 1,9 fold, p=0.001, which is a reduction by 27 fold, p<0.001 or 2 fold, p=0.002, respectively). Inhibition of TLR4 or NFκB signaling diminished C0-C1f-mediated inflammatory responses.

Conclusion

C0-C1f induces inflammation in fibroblasts via TLR4/NFκB signalling pathway. Downregulation of C0-C1f mediated inflammatory responses upon co-stimulation with TGF-β suggests crosstalk between the two signaling pathways. Contrary, C0-C1f reduced TGF-β mediated pro-fibrotic responses reflected by conversion of fibroblasts into myofibroblasts was not observed. Taken together, these data are consistent with the idea that C0-C1f might play a key role in the early initiation of inflammation upon myocardial infarction, also in fibroblasts, and that TGF-β acts as a counterpart at later stages of cardiac remodeling.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): William G. Kerckhoff Stiftung für wissenschaftliche Forschung und Fortbildung

Functional and Structural Properties of Highly Responsive Somatosensory Neurons in Mouse Barrel Cortex

Sparse population activity is a well-known feature of supragranular sensory neurons in neocortex. The mechanisms underlying sparseness are not well understood because a direct link between the neurons activated in vivo, and their cellular properties investigated in vitro has been missing. We used two-photon calcium imaging to identify a subset of neurons in layer L2/3 (L2/3) of mouse primary somatosensory cortex that are highly active following principal whisker vibrotactile stimulation. These high responders (HRs) were then tagged using photoconvertible green fluorescent protein for subsequent targeting in the brain slice using intracellular patch-clamp recordings and biocytin staining. This approach allowed us to investigate the structural and functional properties of HRs that distinguish them from less active control cells. Compared to less responsive L2/3 neurons, HRs displayed increased levels of stimulus-evoked and spontaneous activity, elevated noise and spontaneous pairwise correlations, and stronger coupling to the population response. Intrinsic excitability was reduced in HRs, while we found no evidence for differences in other electrophysiological and morphological parameters. Thus, the choice of which neurons participate in stimulus encoding may be determined largely by network connectivity rather than by cellular structure and function.