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Changes to the Muscle Proteome During Acute Heat Stress are Dependent on Predominant Fiber Type
The objective was to determine acute proteomic changes in muscle caused by heat stress. Crossbred gilts (n=16) were exposed to either thermal neutral (TN, 20°C, 40% relative humidity) or heat stress (HS, 37°C, 40% relative humidity) conditions for 12 hr with ad-libitum feed intake. The semitendinosus was collected, divided into red (RST) and white (WST) portions, and frozen in liquid nitrogen. Protein abundance changes due to treatment were determined (P < 0.15) in sarcoplasmic extracts of HS and TN animals via two-dimensional difference in gel electrophoresis (2D-DIGE). Proteins were identified using electrospray ionization mass spectrometry. Compared to TN muscle, heat shock protein (Hsp) 70, mitochondrial Hsp70, Hsp27, Hsp20, and alpha-B crystallin were increased in abundance in muscle of HS pigs. However, one spot identified as alpha-B crystallin was decreased in abundance in the RST with HS. Several protein spots associated with glycolysis or the TCA cycle were changed in abundance with HS, indicating that muscle energetic metabolism is altered during HS. In the RST, these proteins included aldolase A (decreased, 1 spot), phosphoglycerate kinase 1 (increased, 2 spots), phosphoglycerate mutase 2 (decreased, 1 spot), malate dehydrogenase (increased, 2 spots), succinyl-CoA synthetase (increased, 1 spot), and creatine kinase (increased, 1 spot). In the WST changes in the proteins aldolase A (increased, 1 spot), glyceraldehyde 3-phosphate dehydrogenase (increased, 1 spot), and creatine kinase (decreased, 1 spot) were identified. In both muscle types, beta-enolase (increased, 1 spot), isocitrate dehydrogenase (increased, 1 spot), and malate dehydrogenase (increased, 2 spots) were changed in abundance with HS. Heat stress may also affect cell structure. In the WST, HS altered abundance of proteins involved in microtubule or microfilament structure, including alpha and beta tubulin (decreased, 1 spot each) and cofilin 2 (increased, 1 spot). Finally, abundance of several peroxiredoxins was altered with HS, which may indicate that oxidation regulation is changed during acute HS. In HS pigs, peroxiredoxin 6 was increased in one spot in the RST, and peroxiredoxin 1 was decreased in one spot in the WST. Peroxiredoxin 2 was decreased in abundance in two spots in both muscle types due to HS. These results demonstrate that acute HS may have measurable impacts on muscle metabolism, structure, and antioxidant enzymes, which may contribute to the decreased performance generally observed in HS pigs. Additionally, muscle types may respond and adapt differently to acute HS.
Keywords: Heat Stress, Pigs, Fiber Type