Morphologic analysis of the zebrafish digestive system

Zebrafish ApoB-Containing Lipoprotein Metabolism: A Closer Look

Zebrafish have become a powerful model of mammalian lipoprotein metabolism and lipid cell biology. Most key proteins involved in lipid metabolism, including cholesteryl ester transfer protein, are conserved in zebrafish. Consequently, zebrafish exhibit a human-like lipoprotein profile. Zebrafish with mutations in genes linked to human metabolic diseases often mimic the human phenotype. Zebrafish larvae develop rapidly and externally around the maternally deposited yolk. Recent work revealed that any disturbance of lipoprotein formation leads to the accumulation of cytoplasmic lipid droplets and an opaque yolk, providing a visible phenotype to investigate disturbances of the lipoprotein pathway, already leading to discoveries in MTTP (microsomal triglyceride transfer protein) and ApoB (apolipoprotein B). By 5 days of development, the digestive system is functional, making it possible to study fluorescently labeled lipid uptake in the transparent larvae. These and other approaches enabled the first in vivo description of the STAB (stabilin) receptors, showing lipoprotein uptake in endothelial cells. Various zebrafish models have been developed to mimic human diseases by mutating genes known to influence lipoproteins (eg, ldlra, apoC2). This review aims to discuss the most recent research in the zebrafish ApoB-containing lipoprotein and lipid metabolism field. We also summarize new insights into lipid processing within the yolk cell and how changes in lipid flux alter yolk opacity. This curious new finding, coupled with the development of several techniques, can be deployed to identify new players in lipoprotein research directly relevant to human disease.

A systematic review of advances in intestinal microflora of fish

Intestinal flora is closely related to the health of organisms and the occurrence and development of diseases. The study of intestinal flora will provide a reference for the research and treatment of disease pathogenesis. Upon hatching, fish begin to acquire a microbial community in the intestine. In response to the environment and the host itself, the fish gut eventually develops a unique set of microflora, with some microorganisms being common to different fish. The existence of intestinal microorganisms creates an excellent microecological environment for the host, while the fish symbiotically provides conditions for the growth and reproduction of intestinal microflora. The intestinal flora and the host are interdependent and mutually restrictive. This review mainly describes the formation of fish intestinal flora, the function of normal intestinal flora, factors affecting intestinal flora, and a series of fish models.

Feeding status alters exploratory and anxiety-like behaviors in zebrafish larvae exposed to quinpirole

The dysfunction of dopaminergic signaling is associated with several neurological disorders. The use of pharmacological agents that interact with this signaling system may be employed to understand mechanisms underlying such disorders. Nutritional status can impact dopamine reuptake, receptor affinity, transporter activity, and the effects of drugs that bind to dopamine receptors or interact with dopaminergic system. Here we evaluated the effects of quinpirole (a dopamine D2/D3 receptor agonist) exposure on fed and non-fed zebrafish larvae. Zebrafish larvae (6 days post-fertilization, dpf) were exposed to quinpirole (5.5, 16.7, and 50.0 μM) or water (control group) for one hour. To evaluate the effect of feeding status on quinpirole exposure, the experiments were performed on fed and non-fed animals, a between subject experimental design. Both fed and non-fed quinpirole treated larvae exhibited increased erratic movements compared to controls in an open tank exploration task. No alterations were observed on the main parameters of exploratory behavior and swim activity for non-fed larvae treated with quinpirole compared to controls. However, fed animals exposed to quinpirole exhibited increased locomotor activity, anxiety-like behavior, and repetitive circular movements when compared to controls and non-fed exposed animals. In addition, we observed quinpirole exposure to have no effects on morphological parameters and heartbeat, but to impair optomotor responses in both fed and non-fed larvae compared to control. We also found quinpirole effects to interact with feeding status, as quinpirole-treated fed larvae improved while quinpirole treated non-fed larvae impaired their avoidance reaction towards an aversive stimulus. These results indicate that the behavioral effects of quinpirole exposure depended upon feeding status. They showed that consumption of food, a naturally rewarding stimulus known to engage the dopaminergic system, made this neurotransmitter system more susceptible to quinpirole's effects.

Colon cancer-induced interleukin-35 inhibits beta-catenin-mediated pro-oncogenic activity

The occurrence and development of colon cancer is closely related to inflammation. Therefore, this study was conducted a current retrospective research to study the effect of IL-35 (interleukin 35), a newly identified anti-infective factor, on colon cancer development. The expression of IL-35 in colon cancer samples and their adjacent normal mucosa by real-time PCR, ELISA (enzyme-linked immunosorbent assay). The effect of IL-35 on patient survival, colon cancer progression, and its effect on Wnt/β-catenine signaling pathway was also assessed. IL-35 is minimally expressed in colon cancer tissues but is highly expressed in adjacent normal tissues. The down-regulation of IL-35 was significantly associated with the American Cancer Joint Committee stage and overall survival of colon cancer patients. The overexpression of IL-35 in colon cancer cells inhibits cell migration, invasion, proliferation, colony formation and cancer stem cells by inhibiting beta-catenin. IL-35 inhibits colon neoplasms in mouse. Our results suggest that IL-35 has an inhibitory effect on the development of colon cancer as a novel prognostic indicator and potential therapeutic target.

Ultrastructural Mapping of the Zebrafish Gastrointestinal System as a Basis for Experimental Drug Studies

Research in the field of gastroenterology is increasingly focused on the use of alternative nonrodent model organisms to provide new experimental tools to study chronic diseases. The zebrafish is a particularly valuable experimental platform to explore organ and cell structure-function relationships under relevant biological and pathobiological settings. This is due to its optical transparency and its close-to-human genetic makeup. To-date, the structure-function properties of the GIS of the zebrafish are relatively unexplored and limited to histology and fluorescent microscopy. Occasionally those studies include EM of a given subcellular process but lack the required full histological picture. In this work, we employed a novel combined biomolecular imaging approach in order to cross-correlate 3D ultrastructure over different length scales (optical-, X-ray micro-CT, and high-resolution EM). Our correlated imaging studies and subsequent data modelling provide to our knowledge the first detailed 3D picture of the zebrafish larvae GIS. Our results provide unequivocally a limit of confidence for studying various digestive disorders and drug delivery pathways in the zebrafish.

Intestinal epithelial cell-derived μ-opioid signaling protects against ischemia reperfusion injury through PI3K signaling

Intestinal ischemia has a wide variety of causes, including, but not limited to, atherosclerosis, thrombosis, hypotension, and chronic inflammation. In severe cases, ischemic injury can result in death. μ-Opioid receptor (MOR) signaling has previously been shown to protect against chemically induced colitis, but the cellular origin of this effect remains unknown. Herein, we evaluated the role of intestinal epithelial cell (IEC)-derived MOR signaling in host responses to ischemia/reperfusion-induced injury. Ileal ischemia was accomplished through obstruction of the distal branches of the superior mesenteric artery (60 minutes) and reperfusion for 90 minutes (ischemia-reperfusion). Floxed-MOR mice were crossed to Villin-cre transgenic mice to selectively delete the MOR gene in IECs (MOR(IEC-/-)). Radio-ligand binding assays demonstrated selective loss of MOR signaling in IECs of MOR(IEC-/-) mice. The s.c. administration of the MOR agonist, [D-Arg2, Lys4] dermorphin (1-4) amide (DALDA), 10 minutes before surgery protected against both ischemic and reperfusion phases of intestinal injury, an effect abolished in MOR(IEC-/-) mice. This cytoprotective effect was associated with enterocyte-mediated phosphoinositide 3-kinase (PI3K)/glycogen synthase kinase 3β signaling and decreased apoptosis, as determined by IHC and caspase-3 processing. PI3K blockade with Ly294002 resulted in loss of MOR-mediated cytoprotective function. Together, these data show that IEC-derived μ-opioid signaling uses the PI3K pathway to protect cells against the damaging effect of ischemia-reperfusion. Targeting MOR signaling may represent a novel mean to alleviate intestinal injury and promote the wound-healing response.

Glafenine-induced intestinal injury in zebrafish is ameliorated by μ-opioid signaling via enhancement of Atf6-dependent cellular stress responses

Beside their analgesic properties, opiates exert beneficial effects on the intestinal wound healing response. In this study, we investigated the role of μ-opioid receptor (MOR) signaling on the unfolded protein response (UPR) using a novel zebrafish model of NSAID-induced intestinal injury. The NSAID glafenine was administered to zebrafish larvae at 5 days post-fertilization (dpf) for up to 24 hours in the presence or absence of the MOR-specific agonist DALDA. By analysis with histology, transmission electron microscopy and vital dye staining, glafenine-treated zebrafish showed evidence of endoplasmic reticulum and mitochondrial stress, with disrupted intestinal architecture and halted cell stress responses, alongside accumulation of apoptotic intestinal epithelial cells in the lumen. Although the early UPR marker BiP was induced with glafenine-induced injury, downstream atf6 and s-xbp1 expression were paradoxically not increased, explaining the halted cell stress responses. The μ-opioid agonist DALDA protected against glafenine-induced injury through induction of atf6-dependent UPR. Our findings show that DALDA prevents glafenine-induced epithelial damage through induction of effective UPR.

Dynamic Lkb1-TORC1 signaling as a possible mechanism for regulating the endoderm-intestine transition

The intestinal epithelium arises from undifferentiated endoderm via a developmental program known as the endoderm-intestine transition (EIT). Previously we found that the target of rapamycin complex 1 (TORC1) regulates intestinal growth and differentiation during the EIT in zebrafish. Here we address a possible role for the tumor-suppressor kinase Lkb1 in regulating TORC1 in this context. We find that TORC1 activity is transiently upregulated during the EIT in both zebrafish and mouse. Concomitantly, Lkb1 becomes transiently localized to the nucleus, suggesting that these two phenomena may be linked. Morpholino-mediated knockdown of lkb1 stimulated intestinal growth via upregulation of TORC1, and also induced precocious intestine-specific gene expression in the zebrafish gut epithelium. Knockdown of tsc2, which acts downstream of lkb1, likewise induced early expression of intestine-specific genes. These data suggest that programmed localization of Lkb1 could represent a novel mechanism for regulating the EIT during intestinal development in vertebrates.