Adaptation Of PTL And PPARα To Lipid Metabolism Of Bats

Chiroptera is the second largest order of mammals, which has successfully evolved in the world. Bats are divided into suborders Megachiroptera and Microchiroptera. The megabats take fruits or nectar as food. They distributed in subtropical or tropical latitudes and cannot hibernate. On the other hand, microbats rely on the sophisticated laryngeal echolocation to capture insects. Most species of microbats can survive the extreme environment by hibernation. However, recent molecular phylogenetic studies classify the Chiroptera into Yinpetrochiroptera and Yangochiroptera. Because of the dietary diversification and the ability of deep hibernation, bats are excellent animal models that can be used to explore the adaptation of energy metabolism. Molecular studies revealed that the microbats in Yinpterochiroptera and Yangochiroptera are paraphyletic groups. Based on this recent phylogeny, the adaptation of energy metabolism in gene expression, protein function, and molecular evolution can be deeply explored.The first part of this study focusses on the functional adaptation to dietary fat in bats. We investigated the mRNA expression pattern of pancreatic triacylglycerol lipase (PTL) in bats. The insect-eating bats (e.g., Myotis ricketti and Hipposideros armiger) exhibit a similar gene expression profile of Pnlip in variety tissues, while the frugivorous bat Rousettus leschenaultii has no specific expression patterns for Pnlip. Moreover, the PTL of insectivorous bats show higher activity in breaking down the ester bonds than that in the Old World fruit bat. We provide in vitro evidence, suggesting that the structure of PTL in insect-eating bats is more stable, and both bats show different PTL ability to the catalytic environment when compared with traditional animal models. The PTL also display parallel evolution in insectivorous bats. Our researches expand the understanding of the function of pancreatic lipase on dietary digestion and food habits in mammals.The second part of this dissertation is the adaptation of peroxisome proliferator-activated receptor alpha (PPARa) to hibernation in bats. The critical role of PPARa in metabolic regulation during torpor was shown from the molecular evolution, expression of transcriptional and translational levels, and genome-wide scanning. We conclude that PPARa is adapted to hibernation in bats based on the observations that Ppara has a more stringent functional constraint in the ancestral lineage of hibernating bats and a higher level of expression in hibernating than in non-hibernating bats. We also conclude that PPARa plays a very important role in hibernation as hibernators have more PPARa target genes than non-hibernators, and PPARa in hibernators has a higher binding affinity for its target genes than in non-hibernators.In conclusion, we have explored two key functional factors, PTL and PPARa that involved in diet and hibernation, respectively. Bats exhibit a variety of specialized characters which form the basis for their adaptation in nature. Therefore, studies on these significant characters may enlighten us to expand the understanding of molecular mechanisms in some endocrine system diseases, such as obesity and type Ⅱ diabetes.