Abstract
Hibernation is an adaptive survival strategy in response to cold and foodless winter. To determine the underlying mechanisms of seasonal adaptions, transcriptome sequencing studies have been conducted in bears, ground squirrels and bats. Despite advances in identifying differentially expressed genes involved in metabolism, the precise mechanisms of these physiological adaptions remain unclear. In the present study, we examined liver of Chinese Soft-Shelled Turtle (Pelodiscus sinensis) and found that the contents of lipid droplet (LD) and triglyceride (TG) were significantly decreased during hibernation. Increases in mRNA expression levels of lipolysis-related genes and decreased levels of lipogenesis-related genes during hibernation indicated that LD hydrolysis was stimulated during hibernation. To continuously release fatty acids (FAs) from LD, adipose triglyceride lipase (ATGL) was recruited and accumulated on the surface of LDs via activation of Cyclic Adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling. Meanwhile, increased phosphorylation of the LD-associated protein, perilipin-5, activated the enzyme activity of ATGL via interaction between comparative gene identification-58 (CGI-58) and ATGL. Taken together, our results indicated that ATGL accumulation on the LD surface and its induced enzyme activity during hibernation promoted LD breakdown in the liver of Chinese Soft-Shelled Turtle (Pelodiscus sinensis), thereby enhancing mitochondrial β-oxidation to maintain energy hemostasis.
Highlights
With increased average life expectancy over the past few decades, the global population is aging fast [1]
These results showed that the hepatic lipid droplet (LD) and TG contents in the liver of the Chinese soft-shelled turtle were decreased during hibernation
Using reverse transcription polymerase chain reaction (RT-PCR), we found that the mRNA expression levels of lipolysis-related genes (carnitine palmitoyltransferase 1A (CPT1), peroxisome proliferator activated receptor alpha (PPARα), and apolipoprotein B (APOB)) were increased, whereas the mRNA expression levels of lipogenesis-related genes (fatty acid synthase (FAS), acetyl CoA carboxylase (ACC), sterol regulator element binding protein (SREBP) and malic enzyme (ME)) were decreased in the hibernation group compared with those in the non-hibernation group (Figure 2)
Summary
With increased average life expectancy over the past few decades, the global population is aging fast [1]. The structure or function of physiological systems is slowing, progressively changing and deteriorating in the aging process. The effects of aging on structure and function of body and liver promote the occurrence of chronic liver disease, especially nonalcoholic fatty liver disease (NAFLD) among the elderly [2]. The characteristic feature of NAFLD is liver fat deposition. Despite numerous researches in NAFLD, few effective approaches to degrade hepatic lipid droplet (LD) have been found. The amount of triglyceride (TG) stored as LD in the liver of hibernating animals is significantly increased [5]. LD is gradually degraded [6]
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