Contents lists available at ScienceDirect Fish and Shellfish Immunology journal homepage: www.elsevier.com/locate/fsi Full length article Silencing tyrosine hydroxylase retards depression of immunocompetence of Litopenaeus vannamei under hypothermal stress Ratchaneegorn Mapanao a,1 , Chin-Chyuan Chang b,1 , Winton Cheng b,∗ , Kuan-Fu Liu c,∗∗ a Faculty of Applied Science and Engineering, Khon Khean University, Nong Khai Campus, Nong Khai 43000, Thailand b Department of Aquaculture, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan, ROC c Tungkang Biotechnology Research Center, Fisheries Research Institute, C.O.A, Pingtung 92845, Taiwan, ROC ARTICLE INFO Keywords: Tyrosine hydroxylase Litopenaeus vannamei Hypothermal stress Immunocompetence Catecholamine biosynthesis Carbohydrate metabolite ABSTRACT Tyrosine hydroxylase (TH), the first and rate-limiting step in the synthesis of catecholamines, is required in catecholamine synthesis of the neuroendocrine regulatory network against stress in shrimp. The im- munocompetence, catecholamine biosynthesis, and carbohydrate metabolites were evaluated in Litopenaeus vannamei received L. vannamei TH (LvTH) double-stranded (ds)RNA, diethyl pyrocarbonate-water, or non-tar- geted dsRNA for 3 days then transferred from 28 to 20 or 28 °C. The immunocompetence of LvTH-depleted shrimp held at 28 °C was promoted, and those were downregulated under hypothermal stress and revealed higher level than the other two dsRNA treatments. Meanwhile, the decrease of catecholamine biosynthesis was observed in LvTH-depleted shrimp held at 28 °C, and those were elevated under hypothermal stress and revealed lower levels, compared to two dsRNA treatments. The reduced carbohydrate metabolites was observed in LvTH- depleted shrimp held at 28 °C, and those were upregulated under hypothermal stress and showed lower levels than the other two dsRNA treatments. It was therefore concluded that LvTH-depleted shrimp revealed enhanced immunocompetence and reduced carbohydrate metabolites when exposed to a hypothermal stress condition, and in the meantime, even though catecholamine biosynthesis was downregulated, no significant difference was observed in DA or NE levels. 1. Introduction The Pacific white shrimp, Litopenaeus vannamei (Boone), which has become the major cultivated decapod species in the world, is native to Eastern Pacific coasts. Epidemics associated with viruses and vibriosis have caused serious economic losses to commercial white shrimp farms. Cultured shrimp consistently encounter various environmental stressors especially in rapidly degraded environments of intensive culture sys- tems, and those affect the survival, growth, and physiological and im- munological responses. Relationship of stress and physiology with im- mune resistance are of primary concern. Varying water temperatures are the most-general stressor of aquatic organisms. At temperatures of 20 and 30 °C and salinities above 20‰, L. vannamei revealed the best survival [1], and the growth directly in- creases in the range of 23–30 °C at 33‰ salinity [2]. In crustaceans, the primary response to stress is the release of catecholamines (CAs) to regulate homeostasis, and then induce secondary responses including hyperglycemia and immune suppression [3,4]. In our previous study, hypothermal stress was found to cause increases in dopamine (DA) and norepinephrine (NE) in L. vannamei [5]. Weakened immune responses with increased susceptibility to Vibrio alginolyticus infection [6,7], and also a transient period of modulations in energy metabolism, osmor- egulation, and respiratory responses were noted when L. vannamei re- ceived DA or NE via an injection [8,9]. Those results indicate that hy- pothermal stress-induced catecholamine biosynthesis has a massive influence on immunocompetence and physiological responses in L. vannamei. Tyrosine hydroxylases (THs) are highly conserved enzymes that catalyze the conversion of L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA), which is the precursor for the neurotransmitters, DA, NE, and epinephrine (EP, adrenaline) [10–12]. TH messenger (m)RNA expres- sion can be upregulated by lipopolysaccharide (LPS) in rat phagocytes and Galleria mellonella hemocytes, and by an immune challenge in Manduca sexta hemocytes and fat bodies [13]. In our previous study, TH expression in the brain and hemocytes, and TH activity and glucose level in hemolymph significantly increased in L. vannamei subjected to a https://doi.org/10.1016/j.fsi.2017.11.035 Received 26 August 2017; Received in revised form 10 November 2017; Accepted 17 November 2017 ∗ Corresponding author. ∗∗ Corresponding author. 1 These authors contributed equally as the first author to this work. E-mail addresses: winton@mail.npust.edu.tw (W. Cheng), kuanfu81@yahoo.com.tw (K.-F. Liu). Fish and Shellfish Immunology 72 (2018) 519–527 Available online 21 November 2017 1050-4648/ © 2017 Elsevier Ltd. All rights reserved. T