Christina Lilliehook

Calsenilin: A calcium-binding protein that interacts with the presenilinsand regulates the levels of a presenilin fragment

Most early-onset familial Alzheimer disease (AD) cases are caused by mutations in the highly related genes presenilin 1 (PS1) and presenilin 2 (PS2). Presenilin mutations produce increases in ß-amyloid (Aß) formation and apoptosis in many experimental systems. A cDNA (ALG-3) encoding the last 103 amino acids of PS2 has been identified as a potent inhibitor of apoptosis. Using this PS2 domain in the yeast two-hybrid system, we have identified a neuronal protein that binds calcium and presenilin, which we call calsenilin. Calsenilin interacts with both PS1 and PS2 in cultured cells, and can regulate the levels of a proteolytic product of PS2. Thus, calsenilin may mediate the effects of wild-type and mutant presenilins on apoptosis and on Aß formation. Further characterization of calsenilin may lead to an understanding of the normal role of the presenilins and of the role of the presenilins in Alzheimer disease.

Calsenilin enhances apoptosis by altering endoplasmic reticulum calcium signaling.

Calsenilin (also called DREAM and KChIP3), a member of the neuronal calcium sensor family, was isolated in a yeast two-hybrid screen using an apoptotic domain of presenilin 2 as bait. Calsenilin is a cytoplasmic protein, but interacts with the COOH-termini of both presenilin 1 and presenilin 2 at the endoplasmic reticulum and the Golgi apparatus. In this study, we have investigated calsenilins effect on apoptosis. In stable neuroglioma cell lines, we observed that calsenilin enhances apoptosis in response to serum withdrawal or thapsigargin. Consistent with these observations, caspase and apparently calpain activities were increased during apoptosis in calsenilin-overexpressing cells. Moreover, using calcium imaging we were able to show that cells treated with thapsigargin released more calcium from intracellular stores when calsenilin was overexpressed. Taken together, these data suggest that calsenilin causes cells to be more susceptible to apoptotic triggers, possibly by altering calcium dynamics.

Testosterone-Induced Matrix Metalloproteinase Activation Is a Checkpoint for Neuronal Addition to the Adult Songbird Brain

Testosterone-induced neuronal addition to the adult songbird vocal control center, HVC, requires the androgenic induction of vascular endothelial growth factor (VEGF), followed by VEGF-stimulated angiogenesis. The expanded vasculature acts as a source of BDNF, which supports the immigration of new neurons from the overlying ventricular zone. In tumorigenesis, a similar process of adult angiogenesis is regulated by matrix metalloproteinase (MMP) activity, in particular that of the gelatinases. We therefore investigated the role of the gelatinases in neuronal addition to the HVC of adult female canaries. In situ zymography of the caudal forebrain revealed that testosterone-induced perivascular gelatinase activity that was most prominent in HVC. High-resolution gels revealed distinct MMP activities that comigrated with MMP2 and MMP9, and PCR cloning yielded MMP2 and MMP9 orthologues of 1465 and 1044 bp, respectively. Quantitative PCR revealed that HVC MMP2 mRNA levels doubled within 8 d of testosterone, whereas MMP9 transcript levels were stable. Moreover, isolated adult canary forebrain endothelial cells secreted MMP2, and VEGF substantially increased endothelial MMP2 gelatinase activity. To assess the importance of androgen-regulated, VEGF-induced MMP2 to adult angiogenesis and neurogenesis, we treated testosterone-implanted females with the gelatinase inhibitor SB-3CT. In situ zymography confirmed that SB-3CT suppressed gelatinase activity in HVC, and histological analysis revealed that SB-3CT-treated birds exhibited a decreased endothelial mitotic index and substantially diminished neuronal recruitment to HVC. These data suggest that the androgenic induction of endothelial MMP2 is a critical regulator of neuronal addition to the adult HVC, and as such comprises an important regulatory step in adult neurogenesis.

Brain-derived neurotrophic factor signaling in the HVC is required for testosterone-induced song of female canaries.

Testosterone-induced singing in songbirds is thought to involve testosterone-dependent morphological changes that include angiogenesis and neuronal recruitment into the HVC, a central part of the song control circuit. Previous work showed that testosterone induces the production of vascular endothelial growth factor (VEGF) and its receptor (VEGFR2 tyrosine kinase), which in turn leads to an upregulation of brain-derived neurotrophic factor (BDNF) production in HVC endothelial cells. Here we report for the first time that systemic inhibition of the VEGFR2 tyrosine kinase is sufficient to block testosterone-induced song in adult female canaries, despite sustained androgen exposure and the persistence of the effects of testosterone on HVC morphology. Expression of exogenous BDNF in HVC, induced locally by in situ transfection, reversed the VEGFR2 inhibition-mediated blockade of song development, thereby restoring the behavioral phenotype associated with androgen-induced song. The VEGFR2-inhibited, BDNF-treated females developed elaborate male-like song that included large syllable repertoires and high syllable repetition rates, features known to attract females. Importantly, although functionally competent new neurons were recruited to HVC after testosterone treatment, the time course of neuronal addition appeared to follow BDNF-induced song development. These findings indicate that testosterone-associated VEGFR2 activity is required for androgen-induced song in adult songbirds and that the behavioral effects of VEGFR2 inhibition can be rescued by BDNF within the adult HVC.

Genomic structure, expression pattern, and chromosomal localization of the human calsenilin gene: no association between an exonic polymorphism and Alzheimer's disease.

Calsenilin is a recently-identified member of the neuronal calcium sensor family. Like other members of this family, it is found in the brain and binds calcium. Calsenilin was discovered by virtue of its interaction with both presenilin-1 and -2, proteins that are involved in the etiology of Alzheimers disease. Because calsenilin may play a role in Alzheimers disease and other disease with alterations in calcium homeostasis, we characterized the human gene. The gene, which we localized to chromosome 2, extends over a region of at least 74 kb and includes nine exons. Interestingly, the ninth exon of calsenilin contains a highly polymorphic CA repeat, adjacent to the stop codon. In a study of Alzheimer patients and their unaffected siblings, there was no evidence of association of AD with any calsenilin allele. This CA repeat will be useful for linkage and linkage disequilibrium studies to determine whether calsenilin variants contribute to risk in other diseases.