Co-stimulatory immune checkpoint signalling in cardiac fibrosis: distinct pathological outcomes of ICOS and ICOSL blockade
Z Hegedus, M E Jakab, Sz Farkas, P Ferdinandy, Z V VargaAbstract
Introduction
Cardiac fibroblasts are essential for myocardial repair after injury; however, their overactivation leads to maladaptive fibrosis and progression to heart failure. The Inducible T-cell Co-Stimulator (ICOS) and its Ligand (ICOSL) have emerging roles beyond adaptive immunity, but their contribution to cardiac injury and remodelling remains undefined. Understanding ICOS-ICOSL signalling in the injured myocardium may reveal novel mechanisms regulating fibroblast activation and fibrotic progression.
Purpose
To investigate the role of ICOS-ICOSL signalling in cardiac remodelling and fibrosis in experimental pressure overload.
Methods
Six-month-old male Balb/C mice underwent osmotic mini-pump implantation to receive Angiotensin II (Ang-II; 1.5 mg/kg/day) or saline for 15 days. ICOS or ICOSL signalling was inhibited with monoclonal antibodies (150 µg/dose i.p., every 3 days). Mice were allocated to six groups: Veh/Isotype (n=6), AngII/Isotype (n=16), Veh/anti-ICOS (n=7), AngII/anti-ICOS (n=16), Veh/anti-ICOSL (n=7), and AngII/anti-ICOSL (n=16). Cardiac morpho-functional changes were assessed by echocardiography. Myocardial remodelling and fibrosis were evaluated using histological analysis and qRT-PCR.
Results
Combined Ang-II and ICOS or ICOSL inhibition significantly increased mortality (40-50%), compared with Ang-II alone (13%). Both treatments, when combined with Ang-II, aggravated systolic dysfunction, reducing ejection fraction (EF) and fractional shortening compared to controls. Notably, ICOSL blockade worsened cardiac remodelling, increasing relative wall thickness and left ventricular remodelling index, and reduced EF even as a monotherapy. Myocardial fibrosis was increased in AngII/Isotype and further exacerbated in AngII/anti-ICOSL mice, accompanied by elevated CTGF mRNA expression level. TGF-β and Col1a1 expression were significantly upregulated only following ICOSL inhibition. Differential collagen regulation was observed; ICOS blockade increased Col3a1 expression, whereas ICOSL inhibition increased Col1a1 expression and the Col1a1/Col3a1 ratio, indicating a shift toward a stiffer extracellular matrix phenotype. The Ang-II-induced reduction in the Myh6/Myh7 ratio (hypertrophy marker) was attenuated by ICOS blockade but worsened by ICOSL inhibition. Consistently, NPPB expression and circulating NT-proBNP levels were normalised with ICOS inhibition but remained elevated with ICOSL blockade.
Conclusions
ICOS-ICOSL signalling critically modulates cardiac remodelling under Ang-II-induced stress. ICOS inhibition partially mitigates hypertrophic and fibrotic responses, whereas ICOSL blockade accelerates adverse remodelling, matrix stiffening, and functional decline. These findings identify immune co-stimulatory signalling as a regulator of fibroblast-driven cardiac pathology and highlight the therapeutic potential and risk of targeting this pathway in heart failure.