Expression changes of insulin-like growth factor-1 and its receptor as well as extracellular signal regulated kinase 1/2 in the vestibular epithelium of guinea pigs following gentamycin toxicity

Hongshen SHENG; Yue HE; Guang XU; Jingyu SUN; Jinling WANG

ABSTRACT

BACKGROUND:

Insulin-like growth factor-1 (IGF-1) is an important mitogen and an indispensable regulator during normal hair cell development. Extracellular signal regulated kinase 1/2 (ERK1/2) is also expressed in mammalian vestibular organs.

OBJECTIVE:

To investigate the changes of the expression and the distribution of IGF-1, IGF-1 receptor (IGF-1R) and ERK1/2 in guinea pig's vestibular epithelium following gentamycin injury.

DESIGN:

A randomly controlled study.

SETTING:

Department of Otorhinolaryngology, General Hospital of Chengdu Military Area Command of Chinese PLA.MATERIALS Twenty healthy and adult guinea pigs, weighing 300 to 350 g, provided by the Experimental Animal Center,Fourth Military Medical University of Chinese PLA, were randomly divided into four experimental groups and a control group with 4 in each group.

METHODS:

The experiment was performed at Department of Otorhinolaryngology Research Laboratory of Xijing Hospital,Fourth Military Medical University of Chinese PLA from January 2002 to May 2002. In the experimental groups,gentamycin was intraperitoneally administered daily (80 mg/kg) for 10 consecutive days. For the control group, 1 mL of 0.9% sterile saline was administered in the same way. The guinea pigs, in which unsteady gait or nystagmus appeared,could be involved in the further experiments. Before being sacrificed, the animals' gait, nystagmus and the amount of food-intake were observed every day. The animals were anesthetized deeply with 50 mg/kg pentobarbital 1, 7, 14 or 21days after the last gentamycin administration and then decapitated. Bilateral otic vesicles were harvested and immersed in 4% paraformaldehyde. Then the specimens were decalcified in 10% ethylenediamine tetraacetic acid (EDTA),thereafter embedded in OCT gel and serially sectioned at a thickness of 10 μm in the cryostat. The behavioral changes of guinea pigs were observed. The morphological changes of vestibular epithelium were examined by hematoxylin and eosin (HE) staining. The expression and distribution changes of IGF-1/1R and ERK1/2 were investigated immunohistochemically. MAIN OUTCOME

MEASURES:

The behavioral, morphological, expression and distribution changes of IGF-1/1R and ERK1/2 of guinea pigs in each group.

RESULTS:

Twenty involved guinea pigs entered the stage of final analysis. ① All the guinea pigs' vestibular functions were impaired after gentamycin treatment, then partially restored without any pharmaceutical treatment. ②Morphological injury was obvious after gentamycin treatment, and improved 1 week later. ③The expression of IGF-1/1R was low in the control group, and in the 1-day group it increased significantly to its maximum. After that, its expression decreased gradually, but was still higher in the 21-day group than that in the control group. There were significant differences in the expression of IGF-1/1R among different groups (F =51.8,45.7,P ＜ 0.05). The expression changes of IGF-1 and its receptor were similar. ④The expression of ERK1/2 was low in the control group, and increased gradually after gentamycin toxicity. In the 7-day group, the immunoreactivity reached its maximum. Then the levels of ERK1/2 decreased gradually, but were still higher in the 21-day group than that in the control group. There were significant differences in the expression of ERK1/2 among different groups (F =103.7,106.4, P ＜ 0.01), but no significant differences existed in the expression between ERK1 and ERK2 among different groups (P ＞ 0.05).

CONCLUSION:

The expression of IGF-1/1R and ERK1/2 in vestibular epithelium increased after gentamycin treatment,and IGF-1 may play an important role as an endogenous mitogen through a paracrine or autocrine manner in the early stage of hair cell self-repair of guinea pigs. ERK1/2 may play an important role in signal transduction during vestibular hair cell self-repair after gentamycin toxicity in guinea pigs.