Relations between mitochondrial function and brite adipocytes with feed efficiency and heat production in beef cattle

Abstract

Several studies conducted with molecular biology techniques have focused their hypotheses on mitochondria reporting a possible association with feed efficiency and heat production on beef cattle. In these organelles are the uncoupling protein (UCP), which functions and their interrelationships are not yet fully established. Recently, researchers found inducible adipocytes or brite (beige), which has unique molecular characteristics and development. This new type arises in a process called "browning" of white adipocytes and the emergence of brite adipocytes dissipating energy as heat, is not a desirable trait for beef cattle. Corroborating these findings, researchers have reported the discovery of irisin, a miocin derivate from an extracellular domain of fibronectin type III (FNDC5), which is strongly expressed in skeletal muscle and which may be related to the browning phenomena. In this context, the objectives are investigate the existence and the emergence of brite adipocytes and relating to the differences in feed efficiency and heat production of beef cattle finishing in feedlot. The molecular assay will be confronted with the phenotypes of residual feed intake (RFI) in an attempt to obtain responses that may be interrelated with the basal metabolism and energy loss as heat. Nellore young bulls will be used, selected and grouped according to RFI at Instituto de Zootecnia, Centro APTA Bovinos de Corte (Sertaozinho-SP, Brazil). Groups will be formed by 9 animals each: i) efficient (low RFI); and ii) inefficient (high RFI). The heat production will be estimated by daily measurements of heart rate (HR) and its calibration for the calculation of oxygen consumption (VO2). Immediately slaughter samples will be collected in different regions of deposition of adipose tissue (subcutaneous fat, perirenal, intermuscular and mesenteric). Immunohistochemical assays will be conducted with samples of subcutaneous fat to location of brite adipocytes, using UCP1 antibodies (anti-UCP1). The study of gene expression includes UCP1, PRDM16, Pg-1±, Leptin, Hprt1, DIO2 Cox8b, Cox7a1, COX1 and Cidea (genes involved with thermogenesis). Additionally, proteomic studies will be conducted to test the hypothesis of changes in expression of mitochondrial proteins on the phenotypes of feed efficiency. In the near future, Brazil is expected to produce half of the world's beef, and develop critical technologies through projects like this, it is essential to collect data that can serve as a basis for the development of biomarkers that identify the most efficient animals. (AU)