Chickens from lines artificially selected for juvenile low and high body weight differ in glucose homeostasis and pancreas physiology

Abstract

Early pancreatectomy experiments performed in ducks and pigeons at the end of the 19 th century revealed that avians, unlike mammals, do not display signs of diabetes. Relative to mammals, birds are considered hyperglycemic, displaying fasting blood glucose concentrations twice that of a normal human. While circulating levels of insulin are similar in avians and mammals, and structure and function of the insulin receptor are also conserved among vertebrate species, birds do not experience deleterious effects of chronic hyperglycemia as observed in mammals. Understanding avian glucose homeostasis, particularly in chickens, has both agricultural and biomedical implications.Improvement of feed efficiency and accelerated growth in poultry may come from a greater understanding of the physiological processes associated with glucose utilization in muscle and fat. The chicken has also recently been recognized as an attractive model for human diabetes, where there is a great need for preventative and therapeutic strategies.The link between type 2 diabetes and obesity, coupled with the inherent hyperglycemic nature of chickens, make chickens artificially selected for juvenile low (LWS) and high (HWS) body weight a favorable model for investigating glucose regulation and pancreas physiology. Oral glucose tolerance and insulin sensitivity tests revealed differences in threshold sensitivity to insulin and glucose clearance rate between the lines. Results from real-time PCR showed greater pancreatic mRNA expression of four glucose regulatory genes (preproinsulin, PPI; preproglucagon, PPG; glucose transporter 2, GLUT2; and iii pancreatic duodenal homeobox 1, Pdx1) in LWS, than HWS chickens. Histological analysis of pancreas revealed that HWS chickens have larger pancreatic islets, less pancreatic islet mass, and more pancreatic inflammation than LWS chickens, all of which presumably contribute to impaired glucose metabolism. In summary, results suggest that at selection age, there are differences in pancreas physiology that may explain the differences in glucose regulation between LWS and HWS. These data pave the way for future studies aimed at understanding the developmental regulation of endocrine pancreas function in chickens, as well as how aging affects homeostatic control of blood glucose in chickens.

Convergence in reduced body size, head size, and blood glucose in three island reptiles

“…However, it is also possible that consistently low resource availability on the island is reducing the blood glucose levels through plasticity. Considering the divergence time estimates of 9000–34,000 years, and the consistently low levels across all 3 years, and all three species on the islands, we believe the most likely explanation is that the island habitat has selected for convergent low glucose set points in each of these dwarf populations, similar to what has been demonstrated in dwarf laboratory mice (Borg et al., ; Hauck et al., ), artificial selection on chickens for body size (Smith et al., ; Sumners et al., ) and body type among cattle breeds (Bossaert et al., ; Coleman, Chase, Riley, & Williams, ).…”

“…Research on the evolution of body size on islands has largely focused on ecological selective forces for body size evolution (Case, 1978;Lawlor, 1982;reviewed in Whitakker & Fernández-Palacios 2007), and the physiological differences associated with alterations in island body size have not been hitherto investigated. Divergence in physiological mechanisms regulating body size between island and mainland can be predicted to have occurred as they have in laboratory model organisms and agricultural species artificially selected for body size (Borg, Brown-Borg, & Bartke, 1995;Hauck, Hunter, Danilovich, Kopchick, & Bartke, 2001;Smith, Prall, Siegel, & Cline, 2011;Sumners et al, 2014).…”

“…In addition, glucose level set points (basal levels) can be genetically determined and responsive to selection. For example, genetic strains of mice that have a dwarf phenotype also have low blood glucose relative to wild type strains (Borg et al, 1995;Hauck et al, 2001); Angus and Romosinuano cow breeds have lower blood glucose concentration relative to Brahman cows (Coleman et al 2017); Belgian Blue calves (selected for beef production) have lower blood glucose concentrations relative to Holstein Friesian (selected for milk yield) and East Flemish breeds of calves (selected for milk yield and beef) (Bossaert, Leroy, De Campeneere, De Vliegher, & Opsomer, 2009); and White Plymouth Rock chickens selected for low juvenile body weight have lower blood glucose than those selected for high juvenile body weight (Smith et al, 2011;Sumners et al, 2014). Thus, blood glucose concentrations are determined both genetically and environmentally.…”

Dynamic changes of blood glucose, serum biochemical parameters and gene expression in response to exogenous insulin in Arbor Acres broilers and Silky fowls

“…It showed that the difference in the regulation of blood glucose homeostasis between two breeds may be related to their pancreatic IR levels and fasting insulin levels at the basal state and their different dynamic responses to exogenous insulin. Similarly, hyperphagic low weight chickens successfully return to initial blood glucose levels at 180 min after insulin injection (80 μg/kg weight), whereas hypophagic obese high weight chickens failed to do this 24 . Results suggest that low body weight chickens should have better glucose regulation ability in response to exogenous insulin perturbation.…”

Glucose Tolerance and Plasma Non-Esterified Fatty Acid Levels in Chickens Selected for Low Body Weight, Red Junglefowl, and their Reciprocal Cross

“…Oral glucose tolerance tests are used to assess the pancreatic content of insulin and can be used to characterize differences in hyperglycemic response. While investigating glucose regulation, Sumners et al (2014) observed differences in threshold sensitivity to insulin and glucose clearance rates in lines of chickens divergently selected for high and low juvenile (56 day) body weight. Comparisons of glucose tolerance and plasma NEFA concentrations among RJF, LWS selected for ＞ 50 generations for low body weight, and their reciprocal cross may provide insights regarding metabolic responses.…”