ABSTRACT
Lipid metabolism disorders are found ubiquitously in farmed fish and occur as a result of excessive fat accumulation. Previous studies have found that miR-33 is involved in lipid metabolism; however, its role in fish lipid metabolism is unclear. We sought to clarify this relationship in grass carp in vivo and in vitro. Our findings revealed the length of miR-33 to be 65 bp. Phylogenetic tree analysis showed that grass carp miR-33 was most closely related to fish miR-33 (Siganus canaliculatus). Hepatocytes transfected with miR-33 mimic displayed markedly raised TG content (P < 0.05) as well as increased levels of lipid synthesis-related transcription factors (P < 0.05). Compared with blank and saline groups, total serum cholesterol, AST, and LDL levels were suppressed in groups treated with the miR-33 antagomir (P < 0.05). Moreover, the expression levels of PPARγ and SREBP-1c mRNA were significantly decreased in contrast to those found in the control group (P < 0.05). Similar findings were noted in the expression of immune-related proinflammatory molecules (TNFα, IL-1ß, IL-6, and NF-κB), which also demonstrated decreased levels (P < 0.05). Conversely, high expressions of anti-inflammatory factors (TGF-ß1 and IL-10) were noted (P < 0.05). This investigation strongly supports the role of miR-33 in hepatopancreas-based lipid metabolism and immunity. miR-33 may have been highly conserved in early vertebrates in order to facilitate liver-specific metabolic and immunomodulatory functions. Our findings provide a basis for further investigations exploring the mechanisms surrounding fish lipid metabolism and may aid in preventing and treating immunocompromised fish as well as fish with fatty hepatopancreas, and other metabolic diseases.
