Abstract
Hepatic steatosis is the most common phenomenon of lipid metabolism disorder in farmed fish, but its molecular mechanism is poorly understood. Therefore, the present study was aimed to investigate steatosis induced by high-fat diet (HFD) and explore underlying mechanism in tilapia. The fish were fed on control diet or HFD for 90 days. The blood and liver tissues were collected to determine biochemical parameters, genes expression and proteins level after 30, 60 and 90 days and analyzed lipid accumulation, endoplasmic reticulum (ER) stress and autophagy. After 30 days of feeding, the plasma and hepatic lipid content (TG, TCH, LDL-C and HDL-C) and fatty acids (FAs) transportation (fabp1 and CD36) were enhanced significantly in HFD-fed tilapia. After 60 days, the lipid metabolism disorder, such as increase of TG synthesis and free CH formation, and decrease of FAs β-oxidation and biosynthesis, was observed in liver of HFD-fed tilapia. Further, with increasing lipid accumulation, ER stress was induced and worsen hepatic steatosis via activating IRE1 signaling pathway in liver of HFD group after 90 days. Meanwhile, the autophagy was suppressed via impairing AMPK and BFET pathways in HFD-fed tilapia liver after 90 days. Our results demonstrated that HFD feeding induced extensive lipid deposition, promoted ER stress, suppressed autophagy in tilapia liver. Interestingly, these pathological features were positively correlated with the duration of HFD feeding.
Highlights
Steatosis is the most common phenomenon of lipid metabolism disorder in liver of cultured fish, which results in reduction of growth, feed utilization rate, immunity, stress tolerance, etc. (Dai et al, 2019; Xu et al, 2019)
To investigate steatosis in liver of tilapia fed on high-fat diet (HFD), we observed liver appearance (Figures 1A,B), hematoxylin and eosin (H&E)-stained section (Figures 1C,D), oil red O-stained section (Figures 1E,F) and electron microscopic image (Figures 1G,H)
Considerable steatosis was observed in liver of tilapia fed on HFD after 90 days (Figures 1C,D)
Summary
Steatosis is the most common phenomenon of lipid metabolism disorder in liver of cultured fish, which results in reduction of growth, feed utilization rate, immunity, stress tolerance, etc. (Dai et al, 2019; Xu et al, 2019). Steatosis is the most common phenomenon of lipid metabolism disorder in liver of cultured fish, which results in reduction of growth, feed utilization rate, immunity, stress tolerance, etc. Reasonable high fat in diet can improve the growth of fish (Vergara et al, 1999; Ghanawi et al, 2011). Dietary high fat (15 and 16%) suppressed growth performance, reduced immune capacity and altered lipid metabolism in grass carp (Ctenopharyngodon idella) and tilapia (Oreochromis niloticus) (Ma et al, 2018; Tang et al, 2019). HFD (11 or 12% fat) activated endoplasmic reticulum (ER) stress to mediate hepatic lipid secretion in blunt snout bream (Megalobrama amblycephala) (Cao et al, 2019), and worsen intestinal heath in tilapia (Limbu et al, 2019). Our knowledge about the underlying mechanisms of lipotoxicity induced by HFD is still very limiting
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