Baicalin aggravates isoproterenol-induced myocardial fibrosis via LSD1/AP-1 pathways

Baicalin is one of the main active components of Scutellaria baicalensis Georgi, a traditional herbal medicine. It exhibits a wide range of pharmacological activities, including antibacterial, anti-inflammatory, and antitumor effects. However, its potential side effects-particularly those related to cardiovascular function-remain incompletely understood.

This study aimed to investigate the impact of baicalin on isoproterenol (ISO)-induced ventricular remodeling and to elucidate the underlying mechanisms.

A mouse model of ventricular remodeling was established via continuous subcutaneous infusion of ISO. Cardiac function was evaluated using transthoracic echocardiography after baicalin treatment, while myocardial pathology and collagen deposition were assessed through histological staining. Neonatal rat cardiac fibroblasts (NRCFs) were isolated and subjected to CCK-8, scratch wound healing, and immunofluorescence assays to examine the effects of baicalin on proliferation, migration, and activation of NRCFs, both with and without ISO stimulation. To further explore the mechanism, NRCFs were either treated with an activator protein 1 (AP-1) inhibitor or transfected with a recombinant adenovirus encoding lysine-specific demethylase 1 (LSD1). Protein and mRNA expression levels of relevant targets were analyzed via western blot (WB) and real-time fluorescence quantitative PCR (RT-PCR), respectively.

The data showed that baicalin acted as an independent fibrogenic factor, significantly aggravating ISO-induced ventricular remodeling, particularly myocardial fibrosis, both in vivo and in vitro. ISO pretreatment triggered a signaling cascade in mouse hearts and NRCFs, characterized by the sequential activation of extracellular signal-regulated kinase (ERK) and mitogen- and stress-activated protein kinase 2 (MSK2), resulting in histone H3 phosphorylation at Ser10 (p-H3Ser10) with a concomitant suppression of LSD1 activity. Furthermore, we have found that functioning as an LSD1 inhibitor, baicalin acted synergistically with ISO to further suppress LSD1 activity. This suppression led to the activation of AP-1, which in turn promoted the transcription of type I collagen. Conversely, adenovirus-mediated overexpression of LSD1 in NRCFs reduced the expression of AP-1 subunits (c-Jun and c-Fos) and reversed the pro-fibrotic effects of baicalin under ISO stimulation.

ISO induces myocardial fibrosis by activating the ERK-MSK2-p-H3Ser10 signaling pathway. This leads to the suppression of LSD1 activity. As a natural LSD1 inhibitor, baicalin further suppresses LSD1 activity and exacerbates ISO-induced cardiac fibrosis. Mechanistically, LSD1 inhibition upregulates the transcription factor AP-1. This promotes the transcription of collagen I and drives fibrosis development.