Gonadectomy Down-regulates Expression Of HAP1 In The Arcuate Nucleus Of The Hypothalamus Of 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. In nervous system, HAP1 is highly expressed in arcuate nucleus, periventricular nucleus and median eminence of hypothalamus. Also, in arcuate nucleus, periventricular 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. HAP1's highly expression in these areas indicates HAP1 may be related with HPG function. In order to explore the relationship of HAP1 and HPG, on the basis of altering HAP1 in different gonadal hormone, our study observed the distribution of HAP1 and GnRH in hypothalamus, and the influence of arcuate nucleus, periventricular nucleus and median eminence of HAP1 immunoreactivity in different gonadal hormone level.According to immunohistochemistry ABC method, HAP1 is highly expressed in arcuate nucleus, periventricular nucleus, median eminence, paraventricular nucleus and supraoptic 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. By immunofluorescence double staining, there are many double staining neurons both contained HAP1 and GnRH in arcuate nucleus. But there are few neurons both containing HAP1 and GnRH in periventricular nucleus, median eminence.Our lab has found apparent change of HAP1 both in protein and mRNA levels when gonadectomy or supplementary gonadal hormone. Whether the change is only associated with the function of gonad is unknown. With regard to this, we observed the change of HAP1 in hypothalamus in castration or ovariectomy 3 weeks later group, and castration or ovariectomy 2 weeks later supplementing gonadal hormone 1week group. After castration or ovariectomy 3 weeks, HAP1 immunoreactivity is weakened in arcuate nucleus, periventricular nucleus and median eminence, especially in arcuate nucleus. However, in the other areas of HAP1 distribution there is almost no change. In the group of supplementing gonadal hormone 1 week when castrated or ovariectomized, HAP1's immunoreactivity is as the same as the normal mice.Both of HAP1 and GnRH distribute in arcuate nucleus, periventricular nucleus and median eminence of hypothalamus. Many double staining neurons of HAP1 and GnRH in arcuate nucleus indicate that HAP1 may have a role in GnRH, and regulate HPG.After gonadectomy, because of decreasing of gonadal hormone, there is a little feedback to hypothalamus, so synthesis and secretion of GnRH is increased in 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 arcuate nucleus of hypothalamus changes with gonadal hormone level, indicating HAP1 may participate in transportation and secretion of GnRH.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. Besides, gonadal hormone has a function of nutrition and protection to neurons. After gonadectomy, HAP1's immunoreactivity is weakened, which may be related with the nutrition and protection function of gonadal hormone. Nevertheless, HAP1's immunoreactivity change is mainly in arcuate nucleus, suggesting that it principally results from consumption and metabolism of HAP1 when transporting GnRH.