Analysis Of The Deterioration Of Porcine Meat Quality Responds To Increased Cortisol Based On Transcriptome Sequencing

Stress response is tightly linked to meat quality.The current understanding of the intrinsic mechanism of meat deterioration under stress is limited.As a glucocorticoid(GC),cortisol is a main stress hormone that is secreted by the adrenal cortex,and it is governed by the hypothalamic-pituitary-adrenal(HPA)axis in the stress state.The current understanding of the intrinsic mechanism of meat deterioration under stress is limited.Therefore,this study investigates the intrinsic molecular mechanism of meat deterioration under stress by evaluating the longissimus dorsi(LD),including such parameters as the blood and meat quality index,muscle bundle rate,and apoptosis rate,high-throughput transcriptome sequencing,Western blot,Immunohistochemistry,Q-PCR,and some bioinformatics technology.In addition,this study not only identifies important genes and signalling pathways that may affect the meat quality but also offers a reference for breeding and feeding management to provide consumers with better quality pork products.The results are as followings: 1.The effect of cortisol on meat quality trait and blood indexThe cortisol group was fed the diet with hydrocortisone(natural cortisol),and the longissimus dorsi and blood index were detected after slaughtering.The meat color value at 1 h postmortem in the cortisol group was significantly increased than the control group,and the drip loss at 24 h postmortem in the cortisol group was significantly lower than the control group.Lower protein levels of Desmin,IGF-1,and Myo D1 in the cortisol group compared to the control group,and the protein levels of ATF4,CAST,calpain1,and calpain2 were higher in the cortisol group than the control group.The serum cortisol concentrations in the cortisol group were significantly higher than the control group,and the CK levels in the cortisol group were significantly lower than the control group.2.Cortisol cause muscle damage and muscle cell apoptosisHaematoxylin-eosin(HE)staining revealed severe tissue injuries in the cortisol group,and the cortisol group exhibited a much higher muscle bundle rate than that of the control group.Compared with the control group,the number of apoptotic cells greatly increased,and the apoptosis rate was significantly increased.3.The effect of cortisol on calcium-channel-related and apoptosis-related genesTo determine whether the stress induced meat quality decline is associated with calcium-channel-related genes and apoptosis-related genes,we measured the expression of these genes using Q-PCR technology.Compared with the control group,the cortisol group had significantly higher expression levels of calcium-channel-related genes(SRECA1 and IP3R1)and apoptosis-related genes(BAX,Bcl-2 and Caspase-3).4.Cortisol induces the expression of differential expression genesTLR3 and IL-1RAP were up-regulated in the cortisol group,and their enrichment score were high.The protein expression levels of TLR3 and IL-1RAP of the cortisol group were higher than that of control group based on immunohistochemistry and western blot analysis.A total of 223 DEGs were screened,containing 80 up-regulated genes and 143 down-regulated genes.204 were annotated to the GO database,and 140 were annotated to the KEGG functional pathway.A large number of DEGs related to inflammation,defense response,and damage response were found,such as TLR3,IL-1RAP,TGFβ1,CCL2,SPP1,and GPX2.These genes also influence cell apoptosis.These DEGs may play important roles in the mechanism of cortisol affecting meat quality by regulating each other or other genes.The conclusions of this study are: 1.A large number of DEGs related to calcium channels and cell apoptosis were screened,such as TLR3,IL-1RAP,TGFβ1,CCL2,SPP1,GPX2,CD3ε,CCR5,ATF3,and STC1.Cortisol may regulate the expression of these genes.2.GC induces the apoptosis of skeletal muscle cells by affecting TLR3 and IL-1RAP,which led to NF-κB activation.NF-κB also acted on Caspase-3,Bcl-2,and BAX to induce cell apoptosis,which led to changes in the normal physical and chemical properties of the muscle,ultimately resulting in deteriorated meat quality.