Background: Kidney has long been thought to be a body’s largest organ of elimination for maintaining acid-base balance. In recent years, the research on kidneys has mainly focused on the structural characteristics of the kidney of single age group animals. In this paper we used histological and immunohistochemical methods to observe and compare the structure characteristics of yak kidney and the expression of epidermal growth factor receptor (EGFR), bone morphogenetic protein-2 (BMP-2) and p53 in the kidney of yaks of three different age groups. The aim of the study was to investigate histological characteristics of age-related chan- ges in the kidney of yak and expression and localisation of kidney-related factors. 

Materials and methods: Fifteen healthy male and female yaks from highland plateaus (three groups: newborn, adult and old yaks, n = 5 per group). Histo- logical methods were used to compare the relevant characteristics of the kidney of yaks. The immunohistochemistry method was used to observe the expression and localisation of EGFR, BMP-2, and p53 of the kidney of different ages, and the optical density value was measured and analysed by using image analysis software.

Results: This is an overall observation of the kidney tissue section, which includes the surface of the renal capsule and the internal parenchyma. In the renal parenchyma, there are renal corpuscles, renal tubules. The internal substance included cortex and medulla, which were bounded by the arched artery. In the cortex, there were renal corpuscles, convoluted part of renal tubules (proximal convoluted tubule and distal convoluted tubule) and collecting tubules. The medulla included straight parts of renal tubules (proximal straight tubule and distal straight tubule), thin segments and collecting tubules. It was observed that the organisational structure of the kidney of yaks did not change with age, but the degree of development of the internal structure (glomeruli, renal tubules and collecting tubules) of the kidney changed with age. Immunohistochemical results demonstrated that EGFR and BMP-2-positive reaction in the newborn group was mainly distributed in the proximal tubule epithelial cells, and widely distributed in the adult and old groups. However, the p53-positive reaction was widely distributed in the newborn, adult and old groups. 

Conclusions: The results revealed that the kidney structure tended to be com- pleted with age, and the function of the kidney gradually improved. EGFR and BMP-2 had the effect of promoting kidney development. However, p53 had been widely distributed in the newborn kidney of the yaks. It is suggested that p53 had been involved in cell migration and metabolic differentiation and self-renewal in the new stage.