Prevention of acute liver injury by suppressing plasma kallikrein-dependent activation of latent TGF-b Mengqian Li a, b , Xian-Yang Qin a , Yutaka Furutani a , Ikuyo Inoue a , Sanae Sekihara a , Hiroyuki Kagechika b, c , Soichi Kojima a, b, * a Liver Cancer Prevention Research Unit, RIKEN Center for Integrative Medical Sciences, Saitama, Japan b Graduate School of Medical & Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan c Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo, Japan article info Article history: Received 30 August 2018 Accepted 6 September 2018 Available online xxx Keywords: Plasma kallikrein TGF-b activation Macrophages/Kupffer cells Acute liver injury Proteinase inhibitor abstract Acute liver injury (ALI) is highly lethal acute liver failure caused by different etiologies. Transforming growth factor b (TGF-b) is a multifunctional cytokine and a well-recognized inducer of apoptotic and necrotic cell death in hepatocytes. Latent TGF-b is activated partly through proteolytic cleavage by a serine protease plasma kallikrein (PLK) between the R58 and L59 residues of its propeptide region. Recently, we developed a specific monoclonal antibody to detect the N-terminal side LAP degradation products ending at residue R58 (R58 LAP-DPs) that reflect PLK-dependent TGF-b activation. This study aimed to explore the potential roles of PLK-dependent TGF-b activation in the pathogenesis of ALI. We established a mouse ALI model via the injection of anti-Fas antibodies (Jo2) and observed increases in the TGF-b1 mRNA level, Smad3 phosphorylation, TUNEL-positive apoptotic hepatocytes and R58-positive cells in the liver tissues of Jo2-treated mice. The R58 LAP-DPs were observed in/around F4/80-positive macrophages, while macrophage depletion with clodronate liposomes partly alleviated the Jo2- induced liver injury. Blocking PLK-dependent TGF-b activation using either the serine proteinase in- hibitor FOY305 or the selective PLK inhibitor PKSI-527 or blocking the TGF-b receptor-mediated signaling pathway using SB431542 significantly prevented Jo2-induced hepatic apoptosis and mortality. Further- more, similar phenomena were observed in the mouse model of ALI with the administration of acet- aminophen (APAP). In summary, R58 LAP-DPs reflecting PLK-dependent TGF-b activation may serve as a biomarker for ALI, and targeting PLK-dependent TGF-b activation has potential as a therapeutic strategy for ALI. © 2018 Published by Elsevier Inc. 1. Introduction Acute liver injury (ALI) is a symptom of hepatic illness charac- terized by high morbidity and development over a short duration but without an obvious previous record of liver disease [1]. Different etiological factors, such as infection with hepatic viruses, drug and alcohol use, and other unknown reasons, might cause ALI [2]. The acknowledged major processes of ALI include the apoptosis or necrosis of hepatocytes and physiological disorders in other hepatic cells [3]. During the pathogenesis of ALI, massive hepatocyte apoptosis directly destroys liver function and burdens the immune system, along with various pathological signaling factors and cytokines, including transforming growth factor b (TGF-b), which induces apoptosis in rat fetal hepatocytes or hepatoma cells through the mitochondria-dependent apoptosis pathway via Smad3. Increases in TGF-b at both the mRNA and protein levels have also been observed along with the exacerbation of liver injury in ALI murine models [4]. Overactivation of the Smad3 pathway exacerbated liver damage, while the knockdown of Smad3 relieved liver injury in the anti-Fas (Jo2) antibody-induced ALI mice model [5]. TGF-b is synthesized and released as a latent complex, in which 25-kD, active TGF-b is trapped by its propeptide region (termed la- tency associated protein, LAP) [6]. The latent TGF-b is activated before binding to its receptor, at least in part via proteolytic cleavage by plasma kallikrein (PLK) between the R58 and L59 residues of LAP [7]. We recently developed a specific monoclonal antibody, R58, to * Corresponding author. Liver Cancer Prevention Research Unit, RIKEN Center for Integrative Medical Sciences, 2-1 Hirosawa, Wako, Saitama, Japan. E-mail address: skojima@postman.riken.go.jp (S. Kojima). Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc https://doi.org/10.1016/j.bbrc.2018.09.026 0006-291X/© 2018 Published by Elsevier Inc. Biochemical and Biophysical Research Communications xxx (2018) 1e8 Please cite this article in press as: M. Li, et al., Prevention of acute liver injury by suppressing plasma kallikrein-dependent activation of latent TGF-b, Biochemical and Biophysical Research Communications (2018), https://doi.org/10.1016/j.bbrc.2018.09.026