Delayed Endochondral Ossification in Hsp70 Knock-out Mice Fetuses due to Maternal Hyperthermia

Yoo, Seong Hwan; Lee, Jin; Ahn, Sang Gil; Kim, Won Kyu

Abstract

To investigate the effects of maternal hyperthermia on the endochondral ossification, pregnant Hsp70 knock-out and wild type mice at gestational day (GD)8 were immersed in 43 degree C water bath until their body core temperature reached at 43 degree C. Thereafter, pregnant mice were given more 5 minutes hyperthermic exposure. Fetuses were collected at GD 15 and photographed for external appearance analysis. In addition, heat treated Hsp70 fetuses with external congenital anomalies and heat untreated wild type fetuses were used as experimental and control animals, respectively. Developing humeri at GD 17 were stained with alizarin red S and alcian bue according to the method of Kimmel and Trammell (1981).Developing upper limbs were immunostained for FGF-8, and observed with light and transmission electron microscope. 1.The proportion of average length of the humerus in heat untreated group to heat treated group was 1 :0.58.The proportion of average length of calcified part to average whole length was 1 :0.46 in control and 1 :0.18 in experimental group, respectively. 2.Apical ectodermal ridge was positively reacted to FGF-8 immunohistochemistry in the control group, but not in the experimental group. The humerus of experimental group showed more delayed endochondrial ossification than that of control group. The chondrocytes in the proliferating zone did not react in the experimental group. 3.Collagen fibers were loosely arranged in the experimental group. Mitochondria possessed early staged mitochondrial cristae, i.e.vesicular type in the experimental group. The results of this study suggest that maternal hyperthermia may inhibit the expression of FGF-8 in the developing upper limb, resulting in delayed endochondral bone growth of the humerus.