Sex-hormones and neuroprotection in Alzheimer's disease : insights from mouse models and human forebrain organoids

<jats:p>&lt;p dir="ltr"&gt;Alzheimer's disease (AD) is the most common cause of dementia and is characterized by progressive cognitive decline accompanied by the accumulation of amyloid-ß (Aβ) plaques, neurofibrillary tangles (NFTs), neuroinflammation and neurodegeneration. Women account for approximately two-thirds of individuals living with AD, a disparity that cannot be explained solely by differences in life expectancy. Increasing evidence suggests that sex hormones influence multiple processes involved in AD pathogenesis, including Aβ metabolism, neuroinflammation, synaptic function, and neuronal survival. Among estrogen receptors, estrogen receptor beta (ERβ) has emerged as a promising mediator of neuroprotection, although the underlying mechanisms remain incompletely understood. Furthermore, most experimental models fail to fully capture the complexity of human AD pathology, highlighting the need for complementary approaches.&lt;/p&gt;&lt;p dir="ltr"&gt;The overall aim of this thesis was to investigate sex hormone-related mechanisms of neuroprotection in AD, with particular emphasis on ERβ signaling, and to establish complementary experimental models for studying disease-associated pathology. To address these aims, two knock-in mouse models of AD (&lt;i&gt;App&lt;/i&gt;NL-G-F and &lt;i&gt;App&lt;/i&gt;NL-F) and a human induced pluripotent stem cell-derived ventral forebrain organoid model carrying familial AD-associated &lt;i&gt;APP&lt;/i&gt; mutations were used.&lt;/p&gt;&lt;p dir="ltr"&gt;Paper I investigated the effects of selective ERβ activation in the &lt;i&gt;App&lt;/i&gt;NL-G-F mouse model. Pharmacological activation of ERβ reduced amyloid pathology and improved cognitive performance in both female and male mice without substantially altering &lt;i&gt;APP&lt;/i&gt; processing. Instead, ERβ activation was associated with sex-specific modulation of microglial responses, suggesting that enhanced clearance or containment of Aβ, rather than reduced Aβ production, contributes to the observed neuroprotection.&lt;/p&gt;&lt;p dir="ltr"&gt;Paper II examined the consequences of gonadectomy in female and male &lt;i&gt;App&lt;/i&gt;NL- G-F and &lt;i&gt;App&lt;/i&gt;NL-F mice. Depletion of circulating sex hormones did not uniformly accelerate AD pathology. In &lt;i&gt;App&lt;/i&gt;NL-G-F mice, gonadectomy produced relatively mild or even protective effects, particularly in males. In contrast, prolonged hormone deprivation in aged &lt;i&gt;App&lt;/i&gt;NL-F mice aggravated cognitive impairment and amyloid pathology. Notably, brain estradiol remained detectable following ovariectomy, demonstrating that circulating hormone concentrations do not necessarily reflect the cerebral hormonal environment. Together, these findings indicate that the effects of sex hormone depletion depend on sex, disease stage and aging.&lt;/p&gt;&lt;p dir="ltr"&gt;Paper III extended these studies into a human experimental system by establishing an immunocompetent human ventral forebrain organoid model carrying familial &lt;i&gt;APP&lt;/i&gt; mutations. The organoids progressively developed key AD- associated phenotypes, including elevated Aß42 production and accumulation, tau phosphorylation, astrocytic and oligodendroglial alterations, and increased neuronal excitability while largely preserving intrinsic membrane properties. These findings indicate that the model recapitulates early stages of human AD pathology and provides a platform for investigating multicellular disease mechanisms.&lt;/p&gt;&lt;p dir="ltr"&gt;Collectively, this thesis demonstrates that sex hormone signaling contributes to brain resilience and modulates AD through mechanisms that depend on sex, brain region, age, disease stage, and cellular context. ERβ signaling emerges as a potential mediator of neuroprotection, whereas the consequences of sex hormone depletion vary according to the timing of endocrine changes during disease progression. The work further highlights the importance of studying interactions between neurons and glial cells in AD and establishes a complementary human organoid model that can facilitate mechanistic studies and the development of future therapeutic strategies.&lt;/p&gt;&lt;h3 dir="ltr"&gt;List of scientific papers&lt;/h3&gt;&lt;p dir="ltr"&gt;I. &lt;b&gt;Aphrodite Demetriou&lt;/b&gt;, Birgitta Lindqvist, Heba G. Ali, Mohamed M. Shamekh, Mukesh Varshney, Jose Inzunza, Silvia Maioli, Per Nilsson, Ivan Nalvarte. ERβ mediates sex-specific protection in the &lt;i&gt;App&lt;/i&gt;NL-G-F mouse model of Alzheimer's disease. Biology of Sex Differences. 2025, 16(1), 29. &lt;a href="https://doi.org/10.1186/s13293-025-00711-w" target="_blank" rel="noreferrer"&gt;https://doi.org/10.1186/s13293-025-00711-w&lt;/a&gt;&lt;/p&gt;&lt;p dir="ltr"&gt;II. Patricia Muñoz, Heba G. Ali*, &lt;b&gt;Aphrodite Demetriou&lt;/b&gt;*, Maria Latorre- Leal, Makoto Shimozawa, Ljerka Delac, Tudor-Fabian Troncea-Sandu, Jose Inzunza, Per Nilsson, Silvia Maioli, Ivan Nalvarte. Effects of gonadectomy on brain sex hormone levels and amyloid pathology in male and female &lt;i&gt;App&lt;/i&gt;NL-G-F and &lt;i&gt;App&lt;/i&gt;NL-F mice. Journal of Neuroendocrinology. 2026, 38(3), e70161. *Contributed equally, listed in alphabetical order.&lt;br&gt;&lt;a href="https://doi.org/10.1111/jne.70161"&gt;https://doi.org/10.1111/jne.70161&lt;/a&gt;&lt;/p&gt;&lt;p dir="ltr"&gt;&lt;br&gt;&lt;/p&gt;&lt;p dir="ltr"&gt;III. &lt;b&gt;Aphrodite Demetriou&lt;/b&gt;, Jesus Alarcon-Gil, Nadine Wondra, Silvia Maioli, Luis Enrique Arroyo-Garcia, Dominik Paquet, Ivan Nalvarte. Modeling familial Alzheimer's disease in immunocompetent human brain organoids reveals amyloid pathology and developmental alterations. [Manuscript]&lt;/p&gt;</jats:p>