Rationale Interleukin-1a (IL-1a) released from necrotic cardiomyocytes is hypothesised to stimulate inflammatory responses in cardiac fibroblasts (CF) and contribute to inflammation post-myocardial infarction. Here we describe a murine model with tamoxifen-inducible fibroblast-specific deletion of the IL-1 receptor (IL1R1) for assessing the importance of the IL-1/CF axis in vivo.
Methods IL1R1-/- mice and IL1R1flx/flx mice, co-expressing tamoxifen-inducible Cre-recombinase under the control of a fibroblast-specific promoter (Col1a2-CreER(T)), were crossed to produce hemizygous offspring (IL1R1flx/-). Cre-positive IL1R1flx/- (experimental) and Cre-negative IL1R1flx/- (control) mice aged 2–3 weeks were injected with tamoxifen (100mg/kg, 5 days) and hearts isolated 4–8 weeks later to establish primary CF cultures. The functional effect of IL1R1 deletion was determined by measuring cytokine and MMP expression (qRT-PCR, ELISA) in response to IL-1a or TNFa.
Results Without tamoxifen administration, IL-1a responses in IL1R1flx/flx and IL1R1flx/- CF were identical despite 50% reduction of IL1R1 mRNA in IL1R1flx/- cells. IL1R1-/- CF showed no response to IL-1a. Monoallelic deletion of IL1R1 therefore had no functional impact. With tamoxifen treatment, a further 75% reduction in basal IL1R1 mRNA levels was observed in Cre-positive IL1R1flx/- CF vs. Cre-negative cells. IL-1a-induced MMP-3, MMP-9 and IL-6 mRNA was reduced by 65–75% in CF from tamoxifen-injected Cre-positive IL1R1flx/- mice vs. control. Similar results were obtained for protein secretion. TNFa responses were unaffected by IL1R1 deletion.
Conclusions We have developed a fibroblast-selective IL1R1 knockout mouse in which functional deletion of IL1R1 can be induced in ~75% of CF. The impact of this will be studied in an experimental myocardial infarction model.
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