Moderate coffee/caffeine intake attenuates cardiac remodelling through fibroblast-selective NCX/NFATc3 signalling

Background/Introduction Moderate coffee consumption is associated with improved cardiovascular outcomes in epidemiological studies, but the cellular mechanisms underlying these benefits remain largely unexplored. Purpose This study aimed to define a translational cellular mechanism by which moderate coffee/caffeine consumption attenuates cardiac fibrotic remodelling. Methods Cardiac remodelling was assessed in L-NAME-treated rats receiving moderate coffee or caffeine by echocardiography, cardiac histology, and phenotypic analysis of cardiac fibroblasts (CFs), while signalling pathways were screened in these cells using antibody arrays. Freshly isolated rat CFs and cardiomyocytes, together with primary human CFs, were exposed to physiologically moderate caffeine concentrations and studied using Ca²⁺/Na⁺ live-cell imaging, patch-clamp recordings, molecular docking, and cellular thermal shift assays. Results Moderate coffee and caffeine intake improved cardiac remodelling and systolic function in L-NAME-treated rats independently of blood pressure modulation. Morphological analysis revealed a significant anti-fibrotic effect, characterized by the reversal of reactive interstitial fibrosis, reduced extracellular matrix expansion and CF activation. These benefits were achieved at low micromolar plasma caffeine concentrations, establishing a physiologically relevant window for subsequent mechanistic dissection. Mechanistically, caffeine induced a distinct triphasic Ca2+ response in CFs, but not in cardiomyocytes. Electrophysiological and pharmacological assays confirmed this response was mediated by NCX1-dependent currents occurring without alterations in intracellular Na+ or sarcoplasmic reticulum Ca2+ stores. This selective Ca2+ signature resulted in the targeted inhibition of calcineurin/NFATc3, CAMKII, and NF-κB signalling pathways without affecting canonical TGF-β, MAPK, and AKT pathways, thus suggesting a precise modulation of cellular signalling rather than broad suppression. The cell-type selectivity was driven by differential NCX isoform expression with CFs predominantly expressing NCX1, whereas cardiomyocytes expressing higher levels of NCX3. Molecular docking and cellular thermal shift assays confirmed caffeine’s higher binding affinity and target engagement for the NCX1 isoform. Finally, this mechanism was fully recapitulated in primary human CFs, where low-micromolar caffeine elicited the identical triphasic Ca2+ response and reduced collagen secretion. Conclusions These findings identify CFs as a key cellular target of caffeine and provide a mechanistic framework linking moderate coffee/caffeine consumption to improved cardiac remodelling, whilst highlighting CF NCX/NFATc3 signalling as a potential therapeutic target.