Reduced estrogens, either through aging or postsurgery breast cancer treatment with the oral nonsteroidal aromatase inhibitor letrozole, are linked with declined cognitive abilities. However, a direct link between letrozole and neuronal deficits induced by pathogenic insults associated with aging such as beta amyloid ( ) has not been established. The objective of this study was to determine if letrozole aggravates synaptic deficits concurrent with insult. We examined the effects of letrozole and oligomeric treatment in dissociated and organotypic hippocampal slice cultures. Changes in glial cell morphology, neuronal mitochondria, and synaptic structures upon letrozole treatment were monitored by confocal microscopy, as they were shown to be affected by oligomers. Oligomeric or letrozole alone caused decreases in mitochondrial volume, dendritic spine density, synaptophysin (synaptic marker), and the postsynaptic protein, synaptopodin. Here, we demonstrated that mitochondrial and synaptic structural deficits were exacerbated when letrozole therapy was combined with treatment. Our novel findings suggest that letrozole may increase neuronal susceptibility to pathological insults, such as oligomeric in Alzheimer’s disease (AD). These changes in dendritic spine number, synaptic protein expression, and mitochondrial morphology may, in part, explain the increased prevalence of cognitive decline associated with aromatase inhibitor use. 1. Introduction Currently, aromatase inhibitors, leading to reduction of estradiol synthesis from testosterone, have been favoured in the treatment of breast cancer of postmenopausal women [1]. Letrozole is one such oral nonsteroidal aromatase inhibitor which prevents the aromatase from producing estrogens by competitive, reversible binding to the heme of its cytochrome P450 unit [2, 3]. Patients receiving letrozole have shown deficits in learning and memory [4]. However, it is still unclear if these functional impairments occur because of neurosteroid deficits and if they become exacerbated in the presence of an additional insult associated with aging, such as an excess of soluble, conformationally altered . Such forms of can interact with synapses and cause pronounced degenerative changes, an observation made in brain tissue from postmortem Alzheimer’s disease (AD) patients and animal models [5]. It has been well documented in AD that there are changes in neuronal and glial morphologies such as dendritic spine atrophy and increased glial growth [5, 6]. In contrast to these negative effects caused by , it is well established that
V. F. Semiglazov, V. V. Semiglazov, G. A. Dashyan et al., “Phase 2 randomized trial of primary endocrine therapy versus chemotherapy in postmenopausal patients with estrogen receptor-positive breast cancer,” Cancer, vol. 110, no. 2, pp. 244–254, 2007.
J. V. A. Choate and J. A. Resko, “Paradoxical effect of an aromatase inhibitor, CGS 20267, on aromatase activity in guinea pig brain,” Journal of Steroid Biochemistry and Molecular Biology, vol. 58, no. 4, pp. 411–415, 1996.
B. P. Haynes, M. Dowsett, W. R. Miller, J. M. Dixon, and A. S. Bhatnagar, “The pharmacology of letrozole,” Journal of Steroid Biochemistry and Molecular Biology, vol. 87, no. 1, pp. 35–45, 2003.
V. Shilling, V. Jenkins, L. Fallowfield, and T. Howell, “The effects of hormone therapy on cognition in breast cancer,” Journal of Steroid Biochemistry and Molecular Biology, vol. 86, no. 3-5, pp. 405–412, 2003.
P. Penzes, M. E. Cahill, K. A. Jones, J.-E. Vanleeuwen, and K. M. Woolfrey, “Dendritic spine pathology in neuropsychiatric disorders,” Nature Neuroscience, vol. 14, no. 3, pp. 285–293, 2011.
J. Prange-Kiel, L. Fester, L. Zhou, H. Jarry, and G. M. Rune, “Estrus cyclicity of spinogenesis: underlying mechanisms,” Journal of Neural Transmission, vol. 116, no. 11, pp. 1417–1425, 2009.
R. Vierk, G. Glassmeier, L. Zhou, et al., “Aromatase inhibition abolishes LTP generation in female but not in male mice,” The Journal of Neuroscience, vol. 32, no. 24, pp. 8116–8126, 2012.
P. Polo-Kantola, R. Portin, O. Polo, H. Helenius, K. Irjala, and R. Erkkola, “The effect of short-term estrogen replacement therapy on cognition: a randomized, double-blind, cross-over trial in postmenopausal women,” Obstetrics and Gynecology, vol. 91, no. 3, pp. 459–466, 1998.
E. Hogervorst, J. Williams, M. Budge, W. Riedel, and J. Jolles, “The nature of the effect of female gonadal hormone replacement therapy on cognitive function in post-menopausal women: a meta-analysis,” Neuroscience, vol. 101, no. 3, pp. 485–512, 2000.
O. T. Wolf, B. M. Kudielka, D. H. Hellhammer, S. T？rber, B. S. McEwen, and C. Kirschbaum, “Two weeks of transdermal estradiol treatment in postmenopausal elderly women and its effect on memory and mood: verbal memory changes are associated with the treatment induced estradiol levels,” Psychoneuroendocrinology, vol. 24, no. 7, pp. 727–741, 1999.
T. Duka, R. Tasker, and J. F. McGowan, “The effects of 3-week estrogen hormone replacement on cognition in elderly healthy females,” Psychopharmacology, vol. 149, no. 2, pp. 129–139, 2000.
A. Kugaya, C. N. Epperson, S. Zoghbi et al., “Increase in prefrontal cortex serotonin2A receptors following estrogen treatment in postmenopausal women,” American Journal of Psychiatry, vol. 160, no. 8, pp. 1522–1524, 2003.
V. W. Henderson, “Action of estrogens in the aging brain: dementia and cognitive aging,” Biochimica et Biophysica Acta, vol. 1800, no. 10, pp. 1077–1083, 2010.
D. Caruso, A. M. Barron, M. A. Brown, et al., “Age-related changes in neuroactive steroid levels in 3xTg-AD mice,” Neurobiol Aging, vol. 34, pp. 1080–1089, 2013.
C. R. Overk, P.-Y. Lu, Y.-T. Wang et al., “Effects of aromatase inhibition versus gonadectomy on hippocampal complex amyloid pathology in triple transgenic mice,” Neurobiology of Disease, vol. 45, no. 1, pp. 479–487, 2012.
J. C. Carroll, E. R. Rosario, L. Chang et al., “Progesterone and estrogen regulate Alzheimer-like neuropathology in female 3xTg-AD mice,” Journal of Neuroscience, vol. 27, no. 48, pp. 13357–13365, 2007.
W. Wei, L. N. Nguyen, H. W. Kessels, H. Hagiwara, S. Sisodia, and R. Malinow, “Amyloid beta from axons and dendrites reduces local spine number and plasticity,” Nature Neuroscience, vol. 13, no. 2, pp. 190–196, 2010.
S. Boridy, H. Takahashi, K. Akiyoshi, and D. Maysinger, “The binding of pullulan modified cholesteryl nanogels to Aβ oligomers and their suppression of cytotoxicity,” Biomaterials, vol. 30, no. 29, pp. 5583–5591, 2009.
H. Hsieh, J. Boehm, C. Sato et al., “AMPAR removal underlies Aβ-induced synaptic depression and dendritic spine loss,” Neuron, vol. 52, no. 5, pp. 831–843, 2006.
V. De Paola, S. Arber, and P. Caroni, “AMPA receptors regulate dynamic equilibrium of presynaptic terminals in mature hippocampal networks,” Nature Neuroscience, vol. 6, no. 5, pp. 491–500, 2003.
B. H. G？hwiler, M. Capogna, D. Debanne, R. A. McKinney, and S. M. Thompson, “Organotypic slice cultures: a technique has come of age,” Trends in Neurosciences, vol. 20, no. 10, pp. 471–477, 1997.
R. A. McKinney, M. Capogna, R. Dürr, B. H. G？hwiler, and S. M. Thompson, “Miniature synaptic events maintain dendritic spines via AMPA receptor activation,” Nature Neuroscience, vol. 2, no. 1, pp. 44–49, 1999.
P. Mendez, L. M. Garcia-Segura, and D. Muller, “Estradiol promotes spine growth and synapse formation without affecting pre-established networks,” Hippocampus, vol. 21, no. 12, pp. 1263–1267, 2011.
A. Grimm, Y. A. Lim, A. G. Mensah-Nyagan, J. Gotz, and A. Eckert, “Alzheimer's disease, oestrogen and mitochondria: an ambiguous relationship,” Molecular Neurobiology, vol. 46, pp. 151–160, 2012.
J. W. Simpkins, K. D. Yi, S.-H. Yang, and J. A. Dykens, “Mitochondrial mechanisms of estrogen neuroprotection,” Biochimica et Biophysica Acta, vol. 1800, no. 10, pp. 1113–1120, 2010.
M. Matsuzaki, G. C. R. Ellis-Davies, T. Nemoto, Y. Miyashita, M. Iino, and H. Kasai, “Dendritic spine geometry is critical for AMPA receptor expression in hippocampal CA1 pyramidal neurons,” Nature Neuroscience, vol. 4, no. 11, pp. 1086–1092, 2001.
J. M. Mateos, A. Lüthi, N. Savic et al., “Synaptic modifications at the CA3-CA1 synapse after chronic AMPA receptor blockade in rat hippocampal slices,” Journal of Physiology, vol. 581, no. 1, pp. 129–138, 2007.
L. Fester, L. Zhou, C. Voets et al., “The opposing roles of estradiol on synaptic protein expression in hippocampal cultures,” Psychoneuroendocrinology, vol. 34, supplement 1, pp. S123–S129, 2009.
A. Vlachos, E. Korkotian, E. Schonfeld, E. Copanaki, T. Deller, and M. Segal, “Synaptopodin regulates plasticity of dendritic spines in hippocampal neurons,” Journal of Neuroscience, vol. 29, no. 4, pp. 1017–1033, 2009.
S. C. Janicki and N. Schupf, “Hormonal influences on cognition and risk for Alzheimer's disease,” Current Neurology and Neuroscience Reports, vol. 10, no. 5, pp. 359–366, 2010.
A. Prat, M. Behrendt, E. Marcinkiewicz, et al., “A novel mouse model of Alzheimer's disease with chronic estrogen deficiency leads to glial cell activation and hypertrophy,” Journal of Aging Research, vol. 2011, Article ID 251517, 12 pages, 2011.
J. L. Furman, D. M. Sama, J. C. Gant, et al., “Targeting astrocytes ameliorates neurologic changes in a mouse model of Alzheimer's disease,” The Journal of Neuroscience, vol. 32, pp. 16129–16140, 2012.
F. Liu, M. Day, L. C. Mu？iz et al., “Activation of estrogen receptor-β regulates hippocampal synaptic plasticity and improves memory,” Nature Neuroscience, vol. 11, no. 3, pp. 334–343, 2008.
H. Du, L. Guo, S. Yan, A. A. Sosunov, G. M. McKhann, and S. S. Yan, “Early deficits in synaptic mitochondria in an Alzheimer's disease mouse model,” Proceedings of the National Academy of Sciences of the United States of America, vol. 107, no. 43, pp. 18670–18675, 2010.
S. J. Baloyannis, “Mitochondria are related to synaptic pathology in Alzheimer's disease,” International Journal of Alzheimer's Disease, Article ID 305395, 2011.
J. Y. Sung, O. Engmann, M. A. Teylan, A. C. Nairn, P. Greengard, and Y. Kim, “WAVE1 controls neuronal activity-induced mitochondrial distribution in dendritic spines,” Proceedings of the National Academy of Sciences of the United States of America, vol. 105, no. 8, pp. 3112–3116, 2008.
Y. Rui, J. Gu, K. Yu, H. C. Hartzell, and J. Q. Zheng, “Inhibition of AMPA receptor trafficking at hippocampal synapses by -amyloid oligomers: the mitochondrial contribution,” Molecular Brain, vol. 3, no. 1, article 10, 2010.
X. Zhu, G. Perry, M. A. Smith, and X. Wang, “Abnormal mitochondrial dynamics in the pathogenesis of Alzheimer's disease,” Journal of Alzheimer's Disease, vol. 33, pp. S253–S262, 2013.
E. Trushina, E. Nemutlu, S. Zhang et al., “Defects in mitochondrial dynamics and metabolomic signatures of evolving energetic stress in mouse models of familial alzheimer's disease,” PLoS ONE, vol. 7, no. 2, Article ID e32737, 2012.
