The estrogen myth: potential use of gonadotropin-releasing hormone agonists for the treatment of Alzheimer's disease.

Estrogen and other sex hormones have received a great deal of attention for their speculative role in Alzheimer's disease (AD), but at present a direct connection between estrogen and the pathogenesis of AD remains elusive and somewhat contradictory. For example, on one hand there is a large body of evidence suggesting that estrogen is neuroprotective and improves cognition, and that hormone replacement therapy (HRT) at the onset of menopause reduces the risk of developing AD decades later. However, on the other hand, studies such as the Women's Health Initiative demonstrate that HRT initiated in elderly women increases the risk of dementia. While estrogen continues to be investigated, the disparity of findings involving HRT has led many researchers to examine other hormones of the hypothalamic-pituitary-gonadal axis such as luteinising hormone (LH) and follicle-stimulating hormone. In this review, we propose that LH, rather than estrogen, is the paramount player in the pathogenesis of AD. Notably, both men and women experience a 3- to 4-fold increase in LH with aging, and LH receptors are found throughout the brain following a regional pattern remarkably similar to those neuron populations affected in AD. With respect to disease, serum LH level is increased in women with AD relative to non-diseased controls, and levels of LH in the brain are also elevated in AD. Mechanistically, we propose that elevated levels of LH may be a fundamental instigator responsible for the aberrant reactivation of the cell cycle that is seen in AD. Based on these aforementioned aspects, clinical trials underway with leuprolide acetate, a gonadotropin-releasing hormone agonist that ablates serum LH levels, hold great promise as a ready means of treatment in individuals afflicted with AD.

The p38 pathway is activated in Pick disease and progressive supranuclear palsy: a mechanistic link between mitogenic pathways, oxidative stress, and tau.

In Pick disease and progressive supranuclear palsy (PSP), accumulations of phosphorylated tau are associated with oxidative stress, although the mechanism linking these features remains unknown. However, we suspected that the oxidative stress-induced activation of mitogen-activated protein kinases might lead to tau phosphorylation and accumulation as characteristic inclusion bodies. To test this notion, we investigated whether the activation of mitogen-activated protein kinases is involved in the pathogenesis of Pick disease and PSP. Our results show that the lesions of both Pick disease and PSP are associated with the activation of the p38 pathway (phospho-MKK6 and phospho-p38), one of the best characterized of the mitogen-activated protein kinase pathways. Based on these findings, we propose that the phosphorylation of tau is a direct consequence of the oxidative stress-induced activation of mitogen-activated protein kinases, including p38.