Reduction in ribonucleotide reductase subunit RRM2 associated with alterations in mitochondria proteins, leading to impaired gut health of woody breast chicken

Majid Shakeri^1*Elizabeth Ziabtchenko¹Cailtlin Harris¹Janghan Choi¹Hamid Reza Rafieian Naeini²Woo Kyun Kim²Byungwhi Kong¹Brian Bowker^1*

• ¹USDA-ARS, U.S. National Poultry Research Center, Athens GA, United States
• ²Department of Poultry Science, University of Georgia, Athens GA, United States

The woody breast (WB) condition impairs the quality of chicken breast meat, causing a financial loss for the poultry industry. Recent studies suggest that mitochondria may play a role in muscle and gut health by regulating inflammatory mediators. However, there is limited information available on gut and pancreas health as they relate to WB. Ribonucleotide reductase (RNR), subunit RRM2, is involved in DNA synthesis and mitochondrial function. Inhibition of RRM2 increases gastrointestinal disturbances and apoptosis in pancreatic by disturbing inflammatory mediators and mitochondrial homeostasis. This study aimed to investigate links between RRM2, pancreas and gut health in broilers exhibiting WB. Sixty-eight male broilers were used to collect breast muscle, duodenum and pancreas from 10 broilers exhibiting severe WB and 10 normal (N). Gene expression was measured using qRT-PCR with SYBR reagents. Commercial biochemical assays were used to measure mitochondrial function. To determine if RNR controls mitochondrial functions an RNR inhibitor was tested in vitro on avian muscle-derived cells. Data was analyzed using Prism and t-tests. In tissues, RRM2 expression was lower in muscle (P=0.03), pancreas and duodenum (both P=0.04) vs N. Expression of cytochrome b (Cytb) and mitochondrial uncoupling protein 3 (UCP3) were reduced in muscle (P=0.05 and P=0.002) and pancreas (P=0.009 and P=0.002) for WB, while only Cytb was reduced in duodenum (P=0.04). Total mitochondrial protein and mitochondrial complex-V activity were reduced for WB in muscle (P=0.0006 and P=0.004), pancreas (P=0.01 and P=0.002) and duodenum (P=0.001 and P=0.002), respectively. Broilers with WB had increased malondialdehydeonly in pancreas (P=0.01). Reduced GSH/GSSG ratios in muscle (P=0.01), pancreas (P<0.05) and duodenum (P=0.01) of WB broilers indicate more reactive oxygen species (ROS) in the tissues. In vitro, cells treated with an RNR inhibitor had reduced expression of RRM2 (P˂0.0001), Cytb (P=0.0006) and UCP3 (P=0.002) as well as reduced mitochondrial complex-V activity (P=0.001) and total mitochondrial proteins (P=0.01), indicating that RNR may regulate mitochondrial functions. In conclusion, reduced RRM2 expression may potentially reduce RNR function in muscle, duodenum and pancreas of broilers with WB and alter tissue function by increasing ROS production, mitochondrial abnormalities, and oxidative damage while reducing energy production.