Abstract
The bacterial diseases of tilapia caused by Streptococcus agalactiae have resulted in the high mortality and huge economic loss in the tilapia industry. Matrix metalloproteinase-9 (MMP-9) may play an important role in fighting infection. However, the role of MMP-9 in Nile tilapia against S. agalactiae is still unclear. In this work, MMP-9 cDNA of Nile tilapia (NtMMP-9) has been cloned and characterized. NtMMP-9 has 2043 bp and encodes a putative protein of 680 amino acids. NtMMP-9 contains the conserved domains interacting with decorin and inhibitors via binding forces compared to those in other teleosts. Quantitative real-time-polymerase chain reaction (qPCR) analysis reveals that NtMMP-9 distinctly upregulated following S. agalactiae infection in a tissue- and time-dependent response pattern, and the tissues, including liver, spleen, and intestines, are the major organs against a S. agalactiae infection. Besides, the proteolytic activity of NtMMP-9 is also confirmed by heterologous expression and zymography, which proves the active function of NtMMP-9 interacting with other factors. The findings indicate that NtMMP-9 was involved in immune responses against the bacterial challenge at the transcriptional level. Further work will focus on the molecular mechanisms of NtMMP-9 to respond and modulate the signaling pathways in Nile tilapia against S. agalactiae invasion and the development of NtMMP-9-related predictive biomarkers or vaccines for preventing bacterial infection in the tilapia industry.
Highlights
Matrix metalloproteinases (MMPs) are a family of 28 zinc-dependent endopeptidases [1], and they are widely distributed in all kingdoms of life [2]
The NtMMP-9 gene was cloned according to the information of genome and Matrix metalloproteinase-9 (MMP-9) mRNA of O. niloticus as described in the methods section
The highly conserved sequence PRCGVPD was found in NtMMP-9 (Figure 1), which agrees with the PRCXXPD motif
Summary
Matrix metalloproteinases (MMPs) are a family of 28 zinc-dependent endopeptidases [1], and they are widely distributed in all kingdoms of life [2]. MMPs are secreted as a form of zymogens, and can be activated through the conformational change or cysteine-switch proteolysis [3], which contributes to cleave an extracellular matrix (ECM) and to regulate pathological processes such as inflammation. Inflammatory leukocytes are reported to increase drastically, which leads to a longer period of inflammation in MMP-9 knockout mice following an allergen challenge [7]. These indicate that MMP-9 has significant effects on inflammatory processes
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