Exploring the role of the CD74+ cardiac macrophage subset in trastuzumab cardiotoxicity and its mechanisms

Trastuzumab (TRZ) is the standard treatment for human epidermal growth factor receptor 2 (HER-2) positive breast cancer, but its cardiotoxicity significantly impacts the prognosis and quality of survival of patients, and the underlying mechanism of TRZ-related cardiotoxicity remains incompletely understood. Macrophage subsets better reflect macrophage heterogeneity than the traditional macrophage M1/M2 type polarization classification. CD74, a receptor with strong binding affinity for macrophage migration inhibitory factor, plays an important role in macrophage activation. After successfully constructing a mouse TRZ cardiotoxicity model, flow cytometry indicated that CD74⁺ cardiac macrophages (CMφs) were significantly elevated in the TRZ group. Single-cell data were utilized to identify CD74⁺ CMφs, GO and KEGG analyses of the DEGs were conducted to further validate the CD74/STAT1 signaling pathway. Analyses using RT-PCR, immunofluorescence, and western blot revealed a marked increase in the expression of genes and proteins linked to this pathway in TRZ-treated group. Additionally, levels of inflammation-related factors and the expression of apoptotic proteins was elevated following TRZ treatment. CD74-knockdown RAW 264.7 macrophages cell line were constructed via Lentiviruses carrying CD74 (hU6-MCS-CBh-gcGFP-IRES-puromycin) transfection and co-cultured with HL-1 cardiomyocytes to establish an in vitro TRZ cardiotoxicity model. Western blot analysis of CD74/STAT1 signaling pathway protein levels demonstrated that CD74 knockdown rescued TRZ-induced cellular damage. These findings suggest that TRZ may promote inflammation and apoptosis in cardiomyocytes, leading to cardiotoxicity through the CD74⁺ CMφ subset, which regulates the CD74/STAT1 signaling pathway. CD74⁺ CMφs are anticipated to be a novel intervention target and therapeutic strategy for addressing TRZ-induced cardiotoxicity.