image: Suppression of the TGF-β/Smad pathway via a Smad7/Smurf2-dependent ubiquitination mechanism, and direct disruption of the apoptosis-resistant barrier in HSCs. This work extends the role of CTSK beyond that of a conventional ECM-degrading enzyme to a key regulator of protein homeostasis and cell fate. As a multifunctional regulatory protein, CTSK presents a promising therapeutic target warranting further exploration for the treatment of liver fibrosis.
Credit: Yuemin Nan
Background and Aims
Liver fibrosis is characterized by the excessive deposition of extracellular matrix, a process primarily driven by activated hepatic stellate cells (HSCs), and currently lacks effective therapy. Cathepsin K (CTSK) exhibits context-dependent roles across organ systems in fibrosis, but its function in liver fibrosis is unclear. This study aimed to investigate the role and underlying mechanisms of CTSK during liver fibrosis.
Methods
CTSK expression was analyzed in human fibrotic liver samples via transcriptomic analysis and confirmed in murine fibrosis models. The function of CTSK was investigated in both primary HSCs and LX-2 cells by assessing its effects on cell activation, proliferation, apoptosis, and the underlying signaling pathways following CTSK overexpression. The therapeutic potential was evaluated using an adeno-associated virus serotype 8 to overexpress CTSK in two etiologically distinct murine fibrosis models.
Results
CTSK was upregulated in activated HSCs and fibrotic livers. Furthermore, we discovered that it mediates a negative feedback loop to inhibit the TGF-β/Smad pathway via Smad7/Smurf2-dependent TGF-β receptor-I degradation, thereby suppressing HSC activation and proliferation. CTSK also induced mitochondrial apoptosis through Bax/Bcl-2 imbalance and caspase-3 activation. Together, these actions contribute to the anti-fibrotic effect of CTSK. Notably, adeno-associated virus serotype 8-mediated CTSK overexpression attenuated liver fibrosis across multiple murine models.
Conclusions
Our study demonstrates that elevated CTSK functions as an endogenous protective factor that attenuates liver fibrosis. CTSK mediates negative feedback inhibition of the TGF-β pathway while concurrently promoting the mitochondrial apoptosis pathway. The dual anti-fibrotic mechanisms identify CTSK as a promising therapeutic target for liver fibrosis.
Full text
https://www.xiahepublishing.com/2310-8819/JCTH-2025-00592
The study was recently published in the Journal of Clinical and Translational Hepatology.
The Journal of Clinical and Translational Hepatology (JCTH) is owned by the Second Affiliated Hospital of Chongqing Medical University and published by XIA & HE Publishing Inc. JCTH publishes high quality, peer reviewed studies in the translational and clinical human health sciences of liver diseases. JCTH has established high standards for publication of original research, which are characterized by a study’s novelty, quality, and ethical conduct in the scientific process as well as in the communication of the research findings. Each issue includes articles by leading authorities on topics in hepatology that are germane to the most current challenges in the field. Special features include reports on the latest advances in drug development and technology that are relevant to liver diseases. Regular features of JCTH also include editorials, correspondences and invited commentaries on rapidly progressing areas in hepatology. All articles published by JCTH, both solicited and unsolicited, must pass our rigorous peer review process.
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Journal
Journal of Clinical and Translational Hepatology
Article Title
Cathepsin K Alleviates Liver Fibrosis by Inhibiting the TGF-β/Smad Signaling Pathway and Inducing Hepatic Stellate Cell Apoptosis
Article Publication Date
22-Jan-2026