Although practiced clinically for over 40 years, the use of hematopoietic stem cell (HSC) transplants remains limited by the ability to expand these cells ex vivo. An unbiased screen with primary human HSC identified a purine derivative, StemRegenin 1 (SR1), that promotes the ex vivo expansion of CD34 + cells. Culture of HSC with SR1 led to a fifty-fold increase in cells expressing CD34, and a 17-fold increase in cells that retain the ability to engraft immunodeficient mice. Mechanistic studies show that SR1 acts by antagonizing the aryl hydrocarbon receptor (AhR). The identification of SR1 and AhR modulation as a means to induce ex vivo HSC expansion should facilitate the clinical use of HSC therapy.The identification of pharmacological agents that control adult or embryonic stem cell fate has the potential to facilitate the application of stem cell therapies to a host of diseases (1). Among the best characterized adult stem cells are hematopoietic stem cells (HSC) (2). Although HSC are widely used, their full clinical potential has yet to be realized due to lack of defined culture conditions for their expansion (3). This is especially true of allogeneic HSC transplants where only 50% of candidates can find a HLA-matched adult donor (4). The use of cord blood (CB)-derived HSC is an alternative, since the large number of banked CB units greatly facilitates finding an HLA matched graft (5). However, the low number of HSC in these units has largely restricted the widespread application of CB HSC to the pediatric setting (6). To overcome this limitation, clinicians are transplanting CB units from two donors with encouraging preliminary results (7), which suggests that even a 2-fold increase in HSC number would significantly impact HSC transplantation. Thus, identification of molecules that expand HSC during ex vivo culture has remained an important goal of the field.* To whom correspondence should be addressed. schultz@scripps.edu (P.G.S.); mcooke@gnf.org (M.P.C. Culture conditions optimized for HSC expansion (serum free media supplemented with thrombopoietin, stem cell factor, flt3 ligand, and interleukin-6; referred to as "cytokines" hereafter) (8) result in robust proliferation accompanied by differentiation leading to loss of HSC activity. This differentiation can be followed by the loss of the cell surface proteins CD34 and CD133 which are expressed on HSC and progenitor cells ( Fig. 1A) (9). Thus, to identify molecules that promote HSC expansion, we developed an assay that uses primary human CD34 + cells from the blood of mobilized donors (10) and evaluated CD34 and CD133 expression by confocal microscopy following a 5 day culture (Fig. 1A). Using this assay we screened a library of 100,000 heterocycles (11) and identified a purine derivative (SR1, Fig. 1B) that increases the number of CD34 + cells after 5 to 7 days with an EC 50 of 120 nM (Fig. 1A, fig. S1, and table S1). A structure-activity-relationship study of a 2,6,9-substituted purine library based on SR1 was analyzed. Representative analogs an...

Adolescence is a time of continued brain maturation, particularly in limbic and cortical regions, which undoubtedly plays a role in the physiological and emotional changes coincident with adolescence. An emerging line of research has indicated that stressors experienced during this crucial developmental stage may affect the trajectory of this neural maturation and contribute to the increase in psychological morbidities, such as anxiety and depression, often observed during adolescence. In this review, we discuss the short- and long-term effects of periadolescent stress exposure on the structure and function of the brain. More specifically, we examine how stress at prepubertal and early adolescent stages of development affect the morphological plasticity of limbic and cortical brain regions, as well as the enduring effects of adolescent stress exposure on these brain regions in adulthood. We suggest that, due to a number of converging factors during this period of maturation, the adolescent brain may be particularly sensitive to stress-induced neurobehavioral dysfunctions with important consequences on an individual’s immediate and long-term health and well-being.

Estrogens have direct effects on the brain areas controlling cognition. One of the most studied of these regions is the dorsal hippocampal formation, which governs the formation of spatial and episodic memories. In laboratory animals, most investigators report that estrogen enhances synaptic plasticity and improves performance on hippocampal-dependent cognitive behaviors. This review summarizes work conducted in our laboratory and others toward identifying estrogen's actions in the hippocampal formation, and the mechanisms for these actions. Physiologic and pharmacologic estrogen affects cognitive behavior in mammals, which may be applicable to human health and disease. The effects of estrogen in the hippocampal formation that lead to modulation of hippocampal function include effects on cell morphology, synapse formation, signaling, and excitability that have been studied in laboratory mice, rats, and primates. Finally, estrogen may signal through both nuclear and extranuclear hippocampal estrogen receptors to achieve its downstream effects.

Estrogen (E) treatment induces axospinous synapses in rat hippocampus in vivo and in cultured hippocampal neurons in vitro. To better explore the molecular mechanisms underlying this phenomenon, we have established a mouse model for E action in the hippocampus by using Golgi impregnation to examine hippocampal dendritic spine morphology, radioimmunocytochemistry (RICC) and silver-enhanced immunocytochemistry to examine expression levels of synaptic protein markers, and hippocampal-dependent object-placement memory as a behavioral readout for the actions of E. In ovariectomized mice of several strains and F 1 hybrids, the total dendritic spine density on neurons in the CA1 region was not enhanced by E treatment, a finding that differs from that in the female rat. E treatment of ovariectomized C57BL͞6J mice, however, caused an increase in the number of spines with mushroom shapes. By RICC and silver-enhanced immunocytochemistry, we found that the immunoreactivity of postsynaptic markers (PSD95 and spinophilin) and a presynaptic marker (syntaxin) were enhanced by E treatment throughout all fields of the dorsal hippocampus. In the object-placement tests, E treatment enhanced performance of object placement, a spatial episodic memory task. Taken together, the morphology and RICC results suggest a previously uncharacterized role of E in synaptic structural plasticity that may be interpreted as a facilitation of the spine-maturation process and may be associated with enhancement of hippocampal-dependent memory.D endritic spines are specialized to receive synaptic inputs and to compartmentalize calcium, and changes in spine morphology and function are considered to be important for processes such as learning and memory (1-5). It is, therefore, important to understand how dendritic spine formation and maturation are regulated. Extrinsic factors, such as circulating hormones, influence spine properties in the hippocampus. Estrogen (E) treatment regulates dendritic spine formation in the rat hippocampus in vivo (6-8) and in cultured hippocampal neurons in vitro (9-12). The effects of E on hippocampaldependent cognitive functions were shown also in rats and humans (13-15) and recently in mice and nonhuman primates (16)(17)(18)(19).Dendritic-spine changes include at least two different processes: generation of new spines and maturation of existing spine synapses. These processes are closely linked, with complex biochemical, morphological, and electrophysiological consequences (1,2,20). Spine maturation is a multistep, multifaceted process in which the spines change from thin filopodia-like structures to spines with bigger heads, larger synaptic contact area, shorter and wider spine necks, and newly recruited synaptic proteins (1,3,(20)(21)(22). In cell culture, only the mature type of dendritic spines can recruit ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (2) and, thus, make the transition from silent to functional synapses (23).Studies of E-induced synapse formation in the rat hippocampus have use...

Both the magnitude and the duration of the hormonal stress response change dramatically during neonatal development and aging as well as with prior experience with a stressor. However, surprisingly little is known with regard to how pubertal maturation and experience with stress interact to affect hypothalamic-pituitary-adrenal axis responsiveness. Because adolescence is a period of neurodevelopmental vulnerabilities and opportunities that may be especially sensitive to stress, it is imperative to more fully understand these interactions. Thus, we examined hormonal and neural responses in prepubertal (28 d of age) and adult (77 d of age) male rats after exposure to acute (30 min) or more chronic (30 min/d for 7 d) restraint stress. We report here that after acute stress, prepubertal males exhibited a significantly prolonged hormonal stress response (e.g. ACTH and total and free corticosterone) compared with adults. In contrast, after chronic stress, prepubertal males exhibited a higher response immediately after the stressor, but a faster return to baseline, compared with adults. Additionally, we demonstrate that this differential stress reactivity is associated with differential neuronal activation in the paraventricular nucleus of the hypothalamus, as measured by FOS immunohistochemistry. Using triple-label immunofluorescence histochemistry, we found that a larger proportion of CRH, but not arginine vasopressin, cells are activated in the arginine vasopressin in response to both acute and chronic stress in prepubertal animals compared with adults. These data indicate that experience-dependent plasticity of the hypothalamic-pituitary-adrenal neuroendocrine axis is significantly influenced by pubertal maturation. (Endocrinology 147: 1664 -1674, 2006)

During adolescence the brain shows remarkable changes in both structure and function. The plasticity exhibited by the brain during this pubertal period may make individuals more vulnerable to perturbations, such as stress. Although much is known about how exposure to stress and stress hormones during perinatal development and adulthood affect the structure and function of the brain, relatively little is known about how the pubertal brain responds to stress. Furthermore, it is not clear whether stressors experienced during adolescence lead to altered physiological and behavioral potentials in adulthood, as has been shown for perinatal development. The purpose of this review is to present what is currently known about the pubertal maturation of the hypothalamic-pituitary-adrenal (HPA) axis, the neuroendocrine axis that mediates the stress response, and discuss what is currently known about how stressors affect the adolescent brain. Our dearth of knowledge regarding the effects of stress on the pubertal brain will be discussed in the context of our accumulating knowledge regarding stress-induced neuronal remodeling in the adult. Finally, as the adolescent brain is capable of such profound plasticity during this developmental stage, we will also explore the possibility of adolescence as a period of interventions and opportunities to mitigate negative consequences from earlier developmental insults.

ABSTRACT:The magnitude and duration of the hormonal stress response change dramatically throughout an organism's lifespan. Although much is known about the factors that modulate stress reactivity during adulthood and how neonatal development and aging influence stress responsiveness, we know relatively little about how stress reactivity changes during the juvenile to adult transition. Recent studies in adolescent boys and girls have suggested that stress is an important factor contributing to an individual's vulnerability to various neuropsychological dysfunctions, including anxiety, depression, and drug abuse. Thus, understanding how exposure to stressors during this crucial period of development lead to negative consequences is of paramount importance. A growing body of literature indicates that pubertal organisms react differentially, both physiologically and behaviorally, to a stressor compared to adults. The purpose of this review, therefore, is to discuss the recent findings regarding the pubertal maturation of stress reactivity, while also highlighting future research directions that will aid in our understanding of stress and adolescent mental health and development. ß 2010 Wiley Periodicals, Inc. Dev Psychobiol 52: 244-253, 2010.

No abstract