Effect of Temperature on Endocytosis and Intracellular Transport in the Cell Line SHK-1 Derived from Salmon Head Kidney

Knock down to level up: Reframing RNAi for invertebrate ecophysiology

Comparative ecophysiologists strive to understand physiological problems in non-model organisms, but molecular tools such as RNA interference (RNAi) are under-used in our field. Here, we provide a framework for invertebrate ecophysiologists to use RNAi to answer questions focused on physiological processes, rather than as a tool to investigate gene function. We specifically focus on non-model invertebrates, in which the use of other genetic tools (e.g., genetic knockout lines) is less likely. We argue that because RNAi elicits a temporary manipulation of gene expression, and resources to carry out RNAi are technically and financially accessible, it is an effective tool for invertebrate ecophysiologists. We cover the terminology and basic mechanisms of RNA interference as an accessible introduction for "non-molecular" physiologists, include a suggested workflow for identifying RNAi gene targets and validating biologically relevant gene knockdowns, and present a hypothesis-testing framework for using RNAi to answer common questions in the realm of invertebrate ecophysiology. This review encourages invertebrate ecophysiologists to use these tools and workflows to explore physiological processes and bridge genotypes to phenotypes in their animal(s) of interest.

Superior therapeutic activity of TGF-β-induced extracellular vesicles against interstitial cystitis

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic disease characterized by incapacitating pelvic pain. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) are considered key mediators of the paracrine action of MSCs and show better biological activities than the parent MSCs, especially in the bladder tissue, which may be unfavorable for MSC survival. Here, we produced MSC-EVs using advanced three-dimensional (a3D) culture with exogenous transforming growth factor-β3 (TGF-β3) (T-a3D-EVs). Treatment with T-a3D-EVs led to significantly enhanced wound healing and anti-inflammatory capacities. Moreover, submucosal layer injection of T-a3D-EVs in chronic IC/BPS animal model resulted in restoration of bladder function, superior anti-inflammatory activity, and recovery of damaged urothelium compared to MSCs. Interestingly, we detected increased TGF-β1 level in T-a3D-EVs, which might be involved in the anti-inflammatory activity of these EVs. Taken together, we demonstrate the excellent immune-modulatory and regenerative abilities of T-a3D-EVs as observed by recovery from urothelial denudation and dysfunction, which could be a promising therapeutic strategy for IC/BPS.

Two skin cell lines from wild-type and albino Japanese flounder (Paralichthys olivaceus): establishment, characterization, virus susceptibility, efficient transfection, and application to albinism study

In order to provide an applicable cell platform to study fish pathology and skin pigmentation, two cell lines derived from skin tissues of wild-type and albino Japanese flounder were established and named JFSK_wt and JFSK_alb, respectively. These two cell lines were cultured for 45 passages within approximately 300 days. JFSK_wt and JFSK_alb cells were maintained in Dulbecco's Modified Eagle's Medium and Ham's F-12 Nutrient Mixture (DMEM/F12) supplemented with antibiotics, fetal bovine serum (FBS), 2-mercaptoethanol (2-Me), N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), and basic fibroblast growth factor (bFGF). The optimal growth temperature for JFSK_wt and JFSK_alb cells was 24 °C, and microscopically, the two cell lines were composed of fibroblast-like cells. Chromosomal analysis revealed that JFSK_wt and JFSK_alb cells had an identical diploid karyotype with 2n = 48t. Results of viral inoculation assays revealed that both cell lines shared similar patterns of viral susceptibility to nervous necrosis virus (NNV). High transfection efficiency was observed in JFSK_wt and JFSK_alb cells transfected with a pEGFP-N3 reporter plasmid and Cy3-siRNA. The detection of dermal marker Dermo-1 showed that these two cells were both derived from the dermis. Finally, three genes involved in the melanogenesis pathway, including adenylate cyclase type 5 (adcy5), microphthalmia-associated transcription factor (mitf), and endothelin B receptor (ednrb), were downregulated in JFSK_alb versus JFSK_wt cells. Thus, the two cell lines, sampled from skin tissue of wild-type and albino Japanese flounder will be not only helpful for fish pathogen research but also beneficial for albinism-related gene function studies.

The effect of sterol structure upon clathrin-mediated and clathrin-independent endocytosis

Ordered lipid domains (rafts) in plasma membranes have been hypothesized to participate in endocytosis based on inhibition of endocytosis by removal or sequestration of cholesterol. To more carefully investigate the role of the sterol in endocytosis, we used a substitution strategy to replace cholesterol with sterols that show various raft-forming abilities and chemical structures. Both clathrin-mediated endocytosis of transferrin and clathrin-independent endocytosis of clustered placental alkaline phosphatase were measured. A subset of sterols reversibly inhibited both clathrin-dependent and clathrin-independent endocytosis. The ability of a sterol to support lipid raft formation was necessary for endocytosis. However, it was not sufficient, because a sterol lacking a 3β-OH group did not support endocytosis even though it had the ability to support ordered domain formation. Double bonds in the sterol rings and an aliphatic tail structure identical to that of cholesterol were neither necessary nor sufficient to support endocytosis. This study shows that substitution using a large number of sterols can define the role of sterol structure in cellular functions. Hypotheses for how sterol structure can similarly alter clathrin-dependent and clathrin-independent endocytosis are discussed.

Effects of a Dissostichus mawsoni-CaM recombinant proteins feed additive on the juvenile orange-spotted grouper (Epinephelus coioides) under the acute low temperature challenge

The effects of Dissostichus mawsoni-Calmodulin (Dm-CaM) on growth performance, enzyme activities, respiratory burst, MDA level and immune-related gene expressions of the orange-spotted grouper (Epinephelus coioides) exposed to the acute low temperature stress were evaluated. The commercial diet supplemented with Dm-CaM protein was fed to the groupers for 6 weeks. No significant difference was observed in the specific growth rates, weight gains and survivals. After the feeding trial, the groupers were exposed to acute low temperature challenge. The groupers fed with Dm-CaM additive diet showed a significant decrease in the respiratory burst activity, while the blood cell number increased significantly at 25 °C by comparing with the control and additive control group. The enzymatic activity of SOD, ACP and ALP increased significantly in Dm-CaM additive group, while MDA level maintained stable with the lowest value. qRT-PCR analysis indicated that the up-regulated transcript expressions of CaM, C3, SOD2, LysC and HSPA4 were observed in Dm-CaM additive group. These results indicated that Dm-CaM additive diet may regulate the grouper immune response to the acute low temperature challenge.

Effects of a recombinant complement component C3b functional fragment α2MR (α2-macroglobulin receptor) additive on the immune response of juvenile orange-spotted grouper (Epinephelus coioides) after the exposure to cold shock challenge

The effects of Ec-α2MR (Epinephelus coiodes-α2-macroglobulin receptor) on growth performance, enzymatic activity, respiratory burst, MDA level, total antioxidant capacity, DPPH radical scavenging percentage and immune-related gene expressions of the juvenile orange-spotted grouper were evaluated. The commercial diet supplemented with α2MR additive was used to feed the orange-spotted grouper for six weeks. Although a slight increase was observed in the specific growth rate, survival rate and weight gain, no significance was observed among different group. After the feeding trial, the groupers were exposed to cold stress. Respiratory burst activity and MDA level decreased significantly in α2MR additive group by comparing with the control and additive control group, while a sharp increase of ACP activity, ALP activity, total antioxidant capacity and DPPH radial scavenging percentage was observed in α2MR additive group. qRT-PCR analyses confirmed that the up-regulated mRNA expressions of C3, TNF1, TNF2, IL-6, CTL, LysC, SOD1 and SOD2 were observed in α2MR additive group at 20 °C. These results showed that α2MR additive may moderate the immune response in grouper following cold shock challenge.

Heterozygous null bone morphogenetic protein receptor type 2 mutations promote SRC kinase-dependent caveolar trafficking defects and endothelial dysfunction in pulmonary arterial hypertension

Hereditary pulmonary arterial hypertension (HPAH) is a rare, fatal disease of the pulmonary vasculature. The majority of HPAH patients inherit mutations in the bone morphogenetic protein type 2 receptor gene (BMPR2), but how these promote pulmonary vascular disease is unclear. HPAH patients have features of pulmonary endothelial cell (PEC) dysfunction including increased vascular permeability and perivascular inflammation associated with decreased PEC barrier function. Recently, frameshift mutations in the caveolar structural protein gene Caveolin-1 (CAV-1) were identified in two patients with non-BMPR2-associated HPAH. Because caveolae regulate endothelial function and vascular permeability, we hypothesized that defects in caveolar function might be a common mechanism by which BMPR2 mutations promote pulmonary vascular disease. To explore this, we isolated PECs from mice carrying heterozygous null Bmpr2 mutations (Bmpr2(+/-)) similar to those found in the majority of HPAH patients. We show that Bmpr2(+/-) PECs have increased numbers and intracellular localization of caveolae and caveolar structural proteins CAV-1 and Cavin-1 and that these defects are reversed after blocking endocytosis with dynasore. SRC kinase is also constitutively activated in Bmpr2(+/-) PECs, and localization of CAV-1 to the plasma membrane is restored after treating Bmpr2(+/-) PECs with the SRC kinase inhibitor 3-(4-chlorophenyl)-1-(1,1-dimethylethyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine (PP2). Late outgrowth endothelial progenitor cells isolated from HPAH patients show similar increased activation of SRC kinase. Moreover, Bmpr2(+/-) PECs have impaired endothelial barrier function, and barrier function is restored after treatment with PP2. These data suggest that heterozygous null BMPR2 mutations promote SRC-dependent caveolar trafficking defects in PECs and that this may contribute to pulmonary endothelial barrier dysfunction in HPAH patients.

Establishment and characterization of a head kidney cell line from large yellow croaker Pseudosciaena crocea

A continuous cell line, LYCK, derived from the head kidney of large yellow croaker Pseudosciaena crocea was established and characterized. The LYCK cell line multiplied well in Leibovitz's-15 (L-15) medium supplemented with 10% foetal bovine serum (FBS) at 28° C. This cell line, with a population doubling time of 29·5 h at passage 35, has been subcultured for >70 passages. Microscopically, LYCK cells were fibroblast-like. Chromosomal analysis revealed that the modal diploid chromosome number of LYCK cells was 48, which was identical to that of the P. crocea kidney. The cellular fluorescence could be observed in LYCK cells at 48 h after being transfected with pEGFP-N1 plasmid DNA, indicating that LYCK cells were competent for target gene expression in vitro. The expression of mRNA transcripts of the antiviral immune-related molecules interferon regulatory factor-3 I(ir3), interferon regulatory factor-7 (irf7), melanoma differentiation-associated protein 5 (mda5) was obviously up-regulated in LYCK cells in response to the stimulation with poly (I:C), whereas the expression of mRNA transcripts of the inflammatory cytokines tumour necrosis factor-α2 (tnfTNF-α2), interleukin-8 (il8), CC chemokine (lycCC) was up-regulated by lipopolysaccharide. These results indicated that the LYCK cell line could serve as a valuable tool for studies on immune-related gene functions in vitro.

Establishment and characterization of a new fish cell line from head kidney of half-smooth tongue sole (Cynoglossus semilaevis)

A new cell line (TSHKC) derived from half-smooth tongue sole (Cynoglossus semilaevis) head kidney was developed. The cell line was subcultured for 40 passages over a period of 360 days. The cell line was optimally maintained in minimum essential medium supplemented with HEPES, antibiotics, fetal bovine serum, 2-Mercaptoethanol (2-Me), sodium pyruvate and basic fibroblast growth factor. The suitable growth temperature for TSHKC cells was 24 °C, and microscopically, TSHKC cells were composed of fibroblast-like cells. Chromosome analysis revealed that the TSHKC cell line had a normal diploid karyotype with 2n = 42, contained the heterogametic W chromosome. The TSHKC cell line was found to be susceptible to lymphocystis disease virus. The fluorescent signals were observed in TSHKC when the cells were transfected with green fluorescent protein and red fluorescent protein reporter plasmids.

Effects of dietary thia fatty acids on lipid composition, morphology and macrophage function of Atlantic salmon (Salmo salar L.) kidney

High lipid levels are being used in modern salmonid diets to promote rapid growth; however there is a limiting supply of the traditional fish oils as the fish farming industry expands. One way to utilize the lipid sources better, could be to find ways to stimulate fatty acid (FA) oxidation so that Atlantic salmon use more energy for muscle growth and less for storage in perivisceral adipose tissue. We have previously shown that dietary inclusion of the thia FA tetradecylthioacetic acid (TTA) promoted hepatic beta-oxidation and reduced total body lipid levels. However, dietary TTA also had some negative effects, leading to accumulation of sulfone and sulfoxide metabolites of TTA in the kidney and increasing mortality rates, particularly at low water temperatures. Therefore we also wish to investigate the effects of TTA on kidney function at high and low temperatures, including some immune system parameters. The production of leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) immunoreactive material from exogenously added arachidonic acid in isolated head kidney macrophages was affected by both diet and temperature. The phagocytic activity in these cells was reduced by DTA in the 12 degrees C group and there was significantly higher protein degradation in head kidney macrophages at 12 degrees C compared to 5 degrees C in all dietary groups. Interestingly, the incorporation of thia FAs in the kidney was higher at 5 degrees C (0.3% TTA and 0.6% DTA) than at 12 degrees C (0.1% TTA and 0.5% DTA). Additionally, there were lower levels of saturated FAs, while higher levels of polyunsaturated FAs (PUFAs) in the kidney of TTA fed fish at 5 degrees C. We also observed temperature-independent tubular dilatation and a reduction in the density of melanomacrophages of the kidney in salmon fed TTA. Nevertheless, the mRNA expression of some immune-relevant genes in head kidney tissue was not affected by TTA-inclusion in salmon diets. In conclusion, it is clear that 0.6% TTA-inclusion in the feed leads to changes in the kidney function particularly at low water temperatures.

Is fluid-phase endocytosis conserved in hepatocytes of species acclimated and adapted to different temperatures?

Our primary objective was to determine if rates of fluid-phase endocytosis (FPE) were conserved in hepatocytes from organisms acclimated and adapted to different temperatures. To this aim, the fluorescent dye Lucifer yellow was employed to measure FPE at different assay temperatures (AT) in hepatocytes from 5 degrees C- and 20 degrees C-acclimated trout, Oncorhynchus mykiss (at 5 and 20 degrees C AT), 22 degrees C- and 35 degrees C-acclimated tilapia, Oreochromis nilotica (at 22 and 35 degrees C AT), and the Sprague-Dawley rat (at 10, 20, and 37 degrees C AT). FPE was also studied in rats fed a long-chain polyunsaturated fatty acid (PUFA)-enriched diet (at 10 degrees C AT). Despite being temperature dependent, endocytic rates (values in pl. cell(-1). h(-1)) in both species of fish were compensated after a period of acclimation. For example, in 20 degrees C-acclimated trout, the rate of endocytosis declined from 1.84 to 1.07 when the AT was reduced from 20 to 5 degrees C; however, after a period of acclimation at 5 degrees C, the rate (at 5 degrees C AT) was largely restored (1.80) and almost perfectly compensated (95%). In tilapia, endocytic rates were also temperature compensated, although only partially (36%). Relatively similar rates obtained at 5 degrees C in 5 degrees C-acclimated trout (1.8), at 20 degrees C in 20 degrees C-acclimated trout (1.84), and at 22 degrees C in 22 degrees C-acclimated tilapia (2.2) suggest that endocytic rates are somewhat conserved in these two species of fish. In contrast, the rate in rat measured at 37 degrees C (16.83) was severalfold greater than in fish at their respective body temperatures. A role for lipids in determining rates of endocytosis was supported by data obtained at 10 degrees C in hepatocytes isolated from rats fed a long-chain PUFA-enriched diet: endocytic rates were higher (5.35 pl. cell(-1). h(-1)) than those of rats fed a standard chow diet (2.33 pl. cell(-1). h(-1)). The conservation of endocytic rates in fish may be related to their ability to conserve other membrane characteristics (i.e., order or phase behavior) by restructuring their membrane lipid composition or by modulating the activities of proteins that regulate endocytosis and membrane traffic, whereas the lack of conservation between fish and rat may be due to differences in metabolic rate.

Initial events in infectious salmon anemia virus infection: evidence for the requirement of a low-pH step

We have investigated the initial steps in the interaction between infectious salmon anemia virus (ISAV) and cultured cells from Atlantic salmon (SHK-1 cell line). Using radioactively or fluorescently labelled viral particles we have studied the binding and fusion kinetics and the effect of pH on binding, uptake, and fusion of ISAV to SHK-1 cells and liposomes. As pH in the medium was reduced from 7.5 to 4.5, the association of virus to the cells was nearly doubled. The same effect of pH was observed when fusion between ISAV and liposomes was analyzed. In addition, the binding of ISAV to intact SHK-1 cells and to cell membrane proteins blotted onto filters was neuraminidase sensitive. However, the increased binding induced by low pH was not neuraminidase sensitive, probably reflecting activation of a fusion peptide at low pH. By using confocal fluorescence microscopy, the increased fusion of fluorescently labelled ISAV with the plasma membrane due to low pH could be demonstrated. When vacuolar pH in the cells was raised during inoculation with chloroquine or ammonium chloride, both electron and confocal microscopy showed accumulation of ISAV in endosomes and lysosomes. Production of infectious virus could be increased by lowering the extracellular pH during infection. Furthermore, chloroquine present during virus inoculation also caused a reduction in the synthesis of viral proteins in ISAV-infected cells as well as in the production of infective virus. These results indicate that ISAV binds to sialic acid residues on the cell surface and that the fusion between virus and cell membrane takes place in the acid environment of endosomes. This provides further evidence for a high degree of similarity between ISAV and influenza virus and extends the basis for the classification of this virus as a member of the Orthomyxoviridae family.