Faculty Bibliography

Obesity and overweight, well known risk factors for cardiovascular disease and type 2 diabetes, are now associated with Alzheimer's disease (AD). It remains to be determined if obesity and overweight contribute to the risk of developing AD through modulating levels of amyloid-beta (Abeta), a key molecule in AD pathogenesis. Thus, we investigated whether there were any associations between plasma Abeta levels and body mass index (BMI) or fat mass (FM) in a group of 18 healthy adults. A statistically significant correlation was found between BMI, FM, and plasma levels of Abeta42 (BMI r = 0.602, P = 0.008; FM r = 0.547, P = 0.019), the longer, more pathogenic form of Abeta, but not with plasma levels of the shorter, less pathogenic Abeta40. Although not significant, positive correlations between plasma levels of Abeta42 and levels of insulin and the inflammatory marker C-reactive protein (CRP), along with an inverse trend between plasma Abeta42 levels and levels of high density lipoprotein (HDL) were answered. These results suggest that proteins implicated in inflammation, cardiovascular disease and type 2 diabetes, which in turn are risk factors for AD, may contribute to the associations between BMI/FM and plasma Abeta42 levels. Longitudinal studies involving larger cohorts are required to determine if elevated body fat may predispose individuals to AD through increasing Abeta42 levels throughout early to late adulthood.

The Hedgehog-GLI signaling pathway is important in animal development and tumorigenesis. Recent findings indicate that the growth and survival of human prostate cancer cells rely upon sustained signaling from the Hedgehog-GLI pathway. These findings have prompted a novel rational strategy for therapeutic treatment of prostate tumors, including metastatic tumors.

The Hedgehog-Gli (Hh-Gli) signaling pathway is essential for numerous events during the development of many animal cell types and organs. In particular, it controls neural cell precursor proliferation in dorsal brain structures and regulates the number of neural stem cells in distinct embryonic, perinatal, and adult niches, such as the developing neocortex, the subventricular zone of the lateral ventricle of the forebrain, and the hippocampus. We have proposed that Hh-Gli signaling regulates dorsal brain growth during ontogeny and that its differential regulation underlays evolutionary change in the morphology (size and shape) of dorsal brain structures. It is also critically involved in sporadic brain tumorigenesis--as well as several other human cancer--suggesting that tumors derive from stem cells or progenitors maintaining an inappropriate active Hh-Gli pathway. Importantly, we and others have demonstrated that human sporadic tumors from the brain and other organs require sustained HH-GLI signaling for sustained growth and survival. Modulating HH-GLI signaling thus represents a novel rational avenue to treat, on one hand, brain degeneration and injury by inducing controlled HH-GLI-mediated regeneration and growth, and on the other hand, to combat cancer by blocking its abnormal activity in tumor cells.

The Gli proteins are critical components of multiple processes in development, homeostasis and disease, including neurogenesis and tumorigenesis. However, it is unclear how the Gli code, the sum of their combinatorial positive and negative functions, dictates cell fate and behavior. Using an antisense approach to knockdown gene function in vivo, we find that each of the three Gli proteins is required for the induction of all primary neurons in the amphibian neural plate and regulates the bHLH/Notch neurogenic cascade. Analyses of endogenous Gli function in Gli-mediated neurogenesis and tumorigenesis, and in animal cap assays, reveal specific requirements that are context specific. Nuclear colocalization and binding studies suggest the formation of complexes, with the first two zinc fingers of the Gli five zinc-finger domain acting as a protein-protein interaction site. The Gli proteins therefore appear to form a dynamic physical network that underlies cooperative function, greatly extending the combinatorial possibilities of the Gli code, which may be further fine-tuned in cell fate specification by co-factor function.

The Hedgehog-Gli (Hh-Gli) signaling pathway controls many aspects of tissue patterning, cell proliferation, differentiation and regeneration and regulates cell number in various organs. In adults, the Hh-Gli pathway remains active in a number of stem cells and regenerating tissues. Inappropriate and uncontrolled HH-GLI pathway activation has been demonstrated in a variety of human cancers. Three recent papers show that components of the pathway are expressed in human prostate tumors and, more importantly, that prostate cancers depend on sustained HH-GLI signaling. These data raise the possibility of a new therapeutic approach to treat this often lethal disease.

This study investigated the influence of age on the behavioral responses elicited by psychostimulants in male CD-1 mice. Behavioral activity including locomotion and stereotypy was measured following acute or repeated administration of cocaine, methylphenidate, amphetamine or saline to postweanling (24 days old), periadolescent (33 days old) and adult (60 days old) mice. Postweanling mice exhibited less total and ambulatory activity than periadolescent mice following a single acute injection of cocaine (20 or 30 and 30 mg/kg, respectively). Further, postweanling mice showed less total activity than both periadolescent and adult mice at a dose of 10 mg/kg methylphenidate. Less stereotypy was also seen in postweanling mice when compared to adolescent mice after 30 mg/kg amphetamine. Seven daily injections of cocaine resulted in a heightened behavioral response on day 7 as compared to day 1, indicative of behavioral sensitization in adult and periadolescent, but not postweanling mice. Repeated methylphenidate resulted in increased total activity in adult, but not periadolescent or postweanling mice. None of the animals were sensitized to the behavioral activating effects of amphetamine. The magnitude of behavioral response and the development of sensitization were dependent upon the age of the animal and the agent tested.

Cilia, as motile and sensory organelles, have been implicated in normal development, as well as diseases including cystic kidney disease, hydrocephalus and situs inversus. In kidney epithelia, cilia are proposed to be non-motile sensory organelles, while in the mouse node, two cilia populations, motile and non-motile have been proposed to regulate situs. We show that cilia in the zebrafish larval kidney, the spinal cord and Kupffer's vesicle are motile, suggesting that fluid flow is a common feature of each of these organs. Disruption of cilia structure or motility resulted in pronephric cyst formation, hydrocephalus and left-right asymmetry defects. The data show that loss of fluid flow leads to fluid accumulation, which can account for organ distension pathologies in the kidney and brain. In Kupffer's vesicle, loss of flow is associated with loss of left-right patterning, indicating that the 'nodal flow' mechanism of generating situs is conserved in non-mammalian vertebrates.

Gene products provided by the mother to the embryo determine the body axes in most animals. A recent study in zebrafish proposes that the TGFss signal Squint is one such factor.

Hedgehog (Hh) signaling regulates cell differentiation and patterning in a wide variety of embryonic tissues. In vertebrates, at least three Gli transcription factors (Gli1, Gli2, and Gli3) are involved in Hh signal transduction. Comparative studies have revealed divergent requirements for Gli1 and Gli2 in zebrafish and mouse. Here, we address the question of whether Gli3 function has also diverged in zebrafish and analyze the regulatory interactions between Hh signaling and Gli activity. We find that zebrafish Gli3 has an early function as an activator of Hh target genes that overlaps with Gli1 activator function in the ventral neural tube. In vitro reporter analysis shows that Gli3 cooperates with Gli1 to activate transcription in the presence of high concentrations of Hh. During late somitogenesis stages, Gli3 is required as a repressor of the Hh response. Gli3 shares this repressor activity with Gli2 in the dorsal spinal cord, hindbrain, and midbrain, but not in the forebrain. Consistently, zebrafish Gli3 blocks Gli1-mediated activation of a reporter gene in the absence of Hh in vitro. In the eye, Gli3 is also required for proper ath5 expression and the differentiation of retinal ganglion cells (RGCs). These results reveal a conserved role for Gli3 in vertebrate development and uncover novel regional functions and regulatory interactions among gli genes.

Hedgehog signaling is required for formation and patterning of the anterior pituitary gland. However, the role of Hedgehog in pituitary precursor cell specification and subsequent placode formation is not well understood. We analyzed pituitary precursor cell lineages and find that pitx3 and distal-less3b (dlx3b) expression domains define lens and pituitary precursor positions. We show that pitx3 is required for pituitary pre-placode formation and cell specification, whereas dlx3b and dlx4b are required to restrict pituitary placode size. In smoothened mutant embryos that cannot transduce Hedgehog signals, median pituitary precursors are mis-specified and form an ectopic lens. Moreover, overexpression of sonic hedgehog (shh) blocks lens formation, and derivatives of lens precursors express genes characteristic of pituitary cells. However, overexpression of shh does not increase median pituitary placode size nor does it upregulate patched (ptc) expression in pituitary precursors during early somitogenesis. Our study suggests that by the end of gastrulation, pitx3-expressing cells constitute an equivalence domain of cells that can form either pituitary or lens, and that a non-Hedgehog signal initially specifies this placodal field. During mid-somitogenesis, Hedgehog then acts on the established median placode as a necessary and sufficient signal to specify pituitary cell types.