Cardiac fibrosis: Myofibroblast-mediated pathological regulation and drug delivery strategies

Abstract

Cardiac fibrosis remains an unresolved problem in heart diseases. After initial injury, cardiac fibroblasts (CFs) are activated and subsequently differentiate into myofibroblasts (myoFbs) that are major mediator cells in the pathological remodeling. MyoFbs exhibit proliferative and secretive characteristics, and contribute to extracellular matrix (ECM) turnover, collagen deposition. The persistent functions of myoFbs lead to fibrotic scars and cardiac dysfunction. The anti-fibrotic treatment is hindered by the elusive mechanism of fibrosis and lack of specific targets on myoFbs. In this review, we will outline the progress of cardiac fibrosis and its contributions to the heart failure. We will also shed light on the role of myoFbs in the regulation of adverse remodeling. The communication between myoFbs and other cells that are involved in the heart injury and repair respectively will be reviewed in detail. Then, recently developed therapeutic strategies to treat fibrosis will be summarized such as i) chimeric antigen receptor T cell (CAR-T) therapy with an optimal target on myoFbs, ii) direct reprogramming from stem cells to quiescent CFs, iii) "off-target" small molecular drugs. The application of nano/micro technology will be discussed as well, which is involved in the construction of cell-based biomimic platforms and "pleiotropic" drug delivery systems.

Keywords: Cardiac fibroblast; Cardiac fibrosis; Drug delivery systems; Myocardial remodeling; Myofibroblasts; Reprogramming.

Fig. 1.. Surface markers on differentiated myoFbs.

Due to their extracellular nature, FAP, Frizzled-2 receptor, ATR and TGF-β receptor are reasonable target candidates for the design of myoFb-targeted systems. Interestingly, α_vβ₃ integrins expressed in supermature focal adhesions and their combination are also potential targets. However, because many of these markers are also expressed on other cell types, the specificity needs to be optimized with further studies. Abbreviations: myoFbs, myofibroblasts; FAP, fibroblast activation protein; ATR, angiotensin II receptor; TGF-β, transforming growth factor-β.

Fig. 2.. Representative crosstalk between myoFbs and other cells in cardiac fibrosis.

During cardiac injury, CFs differentiate into myoFbs, leading to ECM deposition and cardiac interstitium expansion. Many molecules are involved in the fibrosis process, including proteins, exosomes and cytokines. For instance, highly expressed Ang II binds ATR in cardiomyocytes and worsens their hypertrophy. Hypertrophic or injured cardiomyocytes alter paracrine signaling which facilitates myoFbs differentiation, while myoFbs in turn also aggravate cardiomyocyte injury. Pro-inflammatory macrophages aggravate fibrosis, while pro-resolution subtypes block myoFb differentiation via paracrine signaling. Abbreviations: CFs, cardiac fibroblasts; myoFbs, myofibroblasts; ECM, extracellular matrix; Ang II, Angiotensin II; ATR, Ang II receptor.

Fig. 3.. FAP CAR-T targets cardiac fibrosis.

a, Scheme of experiments for CAR-T that targets FAP expressing cells. b, Top, Picro-sirium red staining of heart coronal sections in mice to evaluate fibrosis (red) with treatments of saline (left), Ang II/PE (center) or FAP CAR-T cells with Ang II/PE (right). Bottom, magnification of top results to evaluate left ventricular fibrosis. Scale bar, 100 μm. c, Quantitative results of cardiac fibrosis. ****P < 0.0001; one-way ANOVA between groups, P < 0.0001; post hoc multiple comparisons, Tukey’s test; n = 10, 9, and 7 biologically independent mice, from left to right. Abbreviations: Ang II, angiotensin II; PE, phenylephrine [15]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 4.. Flow diagram illustrating the process and protocol of inducing human iPSCs into quiescent CFs.

Using mouse single-cell transcriptomic data, tissue-specific marker gene expressing in fibroblast subpopulations are revealed and used to differentiate human iPSCs-CFs. DEG analysis highlights the critical role of tissue-specific transcription factors in regulating the developmental trajectories of fibroblast subpopulations. Finally, human iPSCs-CFs were generated by sequentially differentiation of intermediate cell types including cardiac progenitor and epicardial cells. Abbreviations: iPSC, induced pluripotent stem cell; CF, cardiac fibroblast; DEG, differentially expressed genes [16].