Mutations in presenilins are responsible for approximately 40% of all early-onset familial Alzheimer disease (FAD) cases in which a genetic cause has been identified. In addition, a number of mutations in presenilin-1 (PS1) have been suggested to be associated with the occurrence of frontal temporal dementia (FTD). Presenilins are highly conserved transmembrane proteins that support cleavage of the amyloid precursor protein by γ-secretase. Recently, we discovered that presenilins also function as passive ER Ca 2+ leak channels. Here we used planar lipid bilayer reconstitution assays and Ca 2+ imaging experiments with presenilin-null mouse embryonic fibroblasts to analyze ER Ca 2+ leak function of 6 FAD-linked PS1 mutants and 3 known FTD-associated PS1 mutants. We discovered that L166P, A246E, E273A, G384A, and P436Q FAD mutations in PS1 abolished ER Ca 2+ leak function of PS1. In contrast, A79V FAD mutation or FTD-associated mutations (L113P, G183V, and Rins352) did not appear to affect ER Ca 2+ leak function of PS1 in our experiments. We validated our findings in Ca 2+ imaging experiments with primary fibroblasts obtained from an FAD patient possessing mutant PS1-A246E. Our results indicate that many FAD mutations in presenilins are loss-of-function mutations affecting ER Ca 2+ leak activity. In contrast, none of the FTD-associated mutations affected ER Ca 2+ leak function of PS1, indicating that the observed effects are disease specific. Our observations are consistent with the potential role of disturbed Ca 2+ homeostasis in Alzheimer disease pathogenesis. IntroductionAlzheimer disease (AD) is the most common form of age-related dementia in human beings over the age of 60 years. AD affects about 2% of populations in industrialized countries. The understanding of the molecular processes that lead to the pathogenesis of AD is immensely important in combatting this neurological disease. Most cases of AD are idiopathic and are characterized by late onset (in individuals over 60 years of age). A small fraction of AD cases (familial AD [FAD]) are characterized by an earlier onset and genetic inheritance. Mutations in presenilin-1 (PS1) and PS2 account for about 40% of all known FAD cases in which a genetic cause has been identified (1). Three missense mutations in PS1 have been suggested to be associated with frontal temporal dementia (FTD) (2), a neurological disorder that affects the frontal and temporal lobes of the brain. Presenilins are 50-kD proteins that contain 9 transmembrane domains (3, 4) and reside in the ER membrane (5). The complex of presenilins, that includes aph-1 and pen-2 subunits, is transported to the cell surface and endosomal structures, where it functions as γ-secretase. The γ-secretase cleaves the amyloid precursor protein (APP) and releases the amyloid β-peptide, the principal constituent of the amyloid plaques in the brains of AD patients. Consistent with the role of presenilins as catalytic subunits of γ-secretase (6, 7), FAD mutations in presenilins affect APP processing.

Estrogens are essential hormones for the regulation of fertility. Cellular responses to estrogens are mediated by estrogen receptor α (ESR1) and estrogen receptor β (ESR2). In mouse and rat models, disruption of Esr1 causes infertility in both males and females. However, the role of ESR2 in reproductive function remains undecided because of a wide variation in phenotypic observations among Esr2-mutant mouse strains. Regulatory pathways independent of ESR2 binding to its cognate DNA response element have also been implicated in ESR2 signaling. To clarify the regulatory roles of ESR2, we generated two mutant rat models: one with a null mutation (exon 3 deletion, Esr2ΔE3) and the other with an inframe deletion selectively disrupting the DNA binding domain (exon 4 deletion, Esr2ΔE4). In both models, we observed that ESR2-mutant males were fertile. ESR2-mutant females exhibited regular estrous cycles and could be inseminated by wild-type (WT) males but did not become pregnant or pseudopregnant. Esr2-mutant ovaries were small and differed from WT ovaries by their absence of corpora lutea, despite the presence of follicles at various stages of development. Esr2ΔE3- and Esr2ΔE4-mutant females exhibited attenuated preovulatory gonadotropin surges and did not ovulate in response to a gonadotropin regimen effective in WT rats. Similarities of reproductive deficits in Esr2ΔE3 and Esr2ΔE4 mutants suggest that DNA binding-dependent transcriptional function of ESR2 is critical for preovulatory follicle maturation and ovulation. Overall, the findings indicate that neuroendocrine and ovarian deficits are linked to infertility observed in Esr2-mutant rats.

Estrogens play pivotal roles in development and function of many organ systems, including the reproductive system. We have generated estrogen receptor 1 (Esr1)-knockout rats using zinc finger nuclease (ZFN) genome targeting. mRNAs encoding ZFNs targeted to exon 3 of Esr1 were microinjected into single-cell rat embryos and transferred to pseudopregnant recipients. Of 17 live births, 5 had biallelic and 1 had monoallelic Esr1 mutations. A founder with monoallelic mutations was backcrossed to a wild-type rat. Offspring possessed only wild-type Esr1 alleles or wild-type alleles and Esr1 alleles containing either 482 bp (Δ482) or 223 bp (Δ223) deletions, indicating mosaicism in the founder. These heterozygous mutants were bred for colony expansion, generation of homozygous mutants, and phenotypic characterization. The Δ482 Esr1 allele yielded altered transcript processing, including the absence of exon 3, aberrant splicing of exon 2 and 4, and a frameshift that generated premature stop codons located immediately after the codon for Thr157. ESR1 protein was not detected in homozygous Δ482 mutant uteri. ESR1 disruption affected sexually dimorphic postnatal growth patterns and serum levels of gonadotropins and sex steroid hormones. Both male and female Esr1-null rats were infertile. Esr1-null males had small testes with distended and dysplastic seminiferous tubules, whereas Esr1-null females possessed large polycystic ovaries, thread-like uteri, and poorly developed mammary glands. In addition, uteri of Esr1-null rats did not effectively respond to 17β-estradiol treatment, further demonstrating that the Δ482 Esr1 mutation created a null allele. This rat model provides a new experimental tool for investigating the pathophysiology of estrogen action.