Alterations Of HAP1 Expression By Castration In The Hypothalamus Of Male Mouse

Huntingtin-associated protein 1 (HAP1) is the first recognized protein, as its binding with huntingtin. HAP1's function is almost unknown. There are at least two isoforms, HAP1A and HAP1B. Both of the two HAP1 are distributed in nervous system and endocrine system. Hypothalamus is a critical area modulating endocrine secretion, it is very important on the regulating for endocrine organs including testicle and ovary. In medial preoptic nucleus, arcuate nucleus and median eminence of hypothalamus, there are the neurons containing GnRH (Gonadotrophin Releasing Hormone). GnRH regulates gonadal hormone by Hypothalamus-Pituitary gland-Gonad (HPG). Gonadal hormone feed back to the GnRH neurons of hypothalamus. Also, in nervous system, HAP1 is highly expressed in medial preoptic nucleus, arcuate nucleus, periventricular nucleus and median eminence of hypothalamus. HAP1's highly expression in these areas indicates HAP1 may be related with HPG function. Our lab has found that many double staining neurons of HAP1 and GnRH in arcuate nucleus, indicating that HAP1 may have a role in GnRH, and regulate HPG.. Our lab has also found apparent change of HAP1 both in protein and mRNA levels when gonadectomy. Wsetern blotting analysis showed that HAP1 lever of mice gonadectomed on 1w was slightly decreased than normal mice, and was progressively cut down on the the 2nd w to 4th w. The male mice that have been gonadectomized for 2 weeks and injected 5mg/kg testosterone for 1 week could return to normal level, moreover, the female mice have been gonadectomized for 2 weeks and injected 240μg/kg estradiol benzoates could retrieve to normal level. In order to explore the relationship of HAP1 and GnRH, our study surveysed the influence about different gonadal hormone level to the expression of HAP1 in hypothalamus, and the influence of medial preoptic nucleus, arcuate nucleus and median eminence of HAP1 immunoreactivity in different gonadal hormone level.According to immunohistochemistry SABC method, HAP1 is highly expressed in ventromedial preoptic nucleus, lateral superior nucleus, paraventricular nucleus, arcuate nucleus, periventricular nucleus, median eminence and supramammillary nucleus, but low expressed in ventromedial nucleus. HAP1 is dispersed adqulisly in cytoplasm and neuropil between cell bodies, and also can be found in stigmoid body.Our lab has found apparent change of HAP1 in protein levels when gonadectomy. Western blotting analysis showed that HAP1 level of mice gonadectomized on the 2nd d to 4th d was significantly increased than normal mice, however, the expression of HAP1 was progressively cut down on the 7th d to 3rd w. With regard to this, we observed the immunoreactivity change of HAP1 in hypothalamus in castration 2 days later group. After castration HAP1 immunoreactivity is accentuated in ventromedial preoptic nucleus, arcuate nucleus where GnRH expresses. However, in the other areas of HAP1 distribution without GnRH expressing there is almost no change.After gonadectomy, because of decreasing of gonadal hormone, there is a little feedback to hypothalamus, so synthesis and secretion of GnRH is increased in medial preoptic nucleus, arcuate nucleus, periventricular nucleus and median eminence of hypothalamus. Some initial studies indicated that HAP1 was associated with microbule and synaptic vesicle, and participated in the vesicle transportation, substance receptor recycle and substance releasing in neurons. HAP1's immunoreactivity in medial preoptic nucleus, arcuate nucleus of hypothalamus changes with gonadal hormone level, indicating HAP1 may participate in transportation and secretion of GnRH.Short time after gonadectomy, enhancing immunoreactivity of HAP1 may result from much more need of transportation and secretion of GnRH. However, long time after gonadectomy weakening immunoreactivity of HAP1 may result from a lot of consumption and metabolism of HAP1 as a function of transportation and secretion of GnRH.