Practical application of the basic aspects of membrane trafficking and receptor-mediated signaling on issues related to animal agriculture

Abstract Text: Because of the relatively short lifespans of beef cattle, membrane trafficking in relation to inflammation is not considered important unless it overtly affects productivity.  However, glucose uptake and utilization is important for adipose tissue development in beef cattle, and increasing glucose utilization in intramuscular adipose tissue can increase carcass quality.  Research from the 1980s demonstrated a lack of insulin sensitivity in isolated bovine adipocytes and adipose tissue explants incubated in vitro.   Insulin did not stimulate glucose or acetate incorporation into fatty acids, nor did it increase concentrations of glycolytic intermediates in bovine adipose tissue incubated with exogenous glucose.   Specific binding of [I125]iodoinsulin and insulin degradation in bovine isolated adipocytes was low to non-detectable.  These early studies indicated that insulin-dependent receptor-mediated signaling was less important in bovine adipose tissue than in adipose tissues of humans or laboratory species.  Recent research demonstrated that GLUT4 expression in muscle and adipose tissue declined markedly after birth in calves, indicating the development of insulin resistance as cattle transitioned from suckling to functional ruminants.  Insulin resistance is important in dairy cattle, and causes ketosis and fatty liver.  In dairy cattle, s.c. adipose tissue GLUT4 expression decreased 50% following parturition, although insulin responsiveness in s.c. adipose tissue was restored as early as 3 wk postpartum.  Expression of genes associated with insulin responsiveness (IRS1, INSIG2, SREBF1, and ZFP423) was upregulated in similar fashion.  Understanding the underlying mechanisms of insulin resistance and inflammation would increase animal health and thereby improve productivity.

Keywords: adipose tissue, bovine, insulin