C-kit ligand (Stem Cell Factor) affects neuronal activity, stimulates pituitary-adrenal axis and prolactin secretion in rats

Characterization of Neurogenic Potential of Dental Pulp Stem Cells Cultured in Xeno/Serum-Free Condition: In Vitro and In Vivo Assessment

Neural stem cells (NSCs) have a high potency for differentiation to neurons and glial cells for replacement of damaged cells and paracrine effects for the regeneration and remyelination of host axons. Dental pulp is known to have a potential to differentiate into neural-like cells; therefore, dental pulp may be used as an autologous cell source for neural repair. In this study, we selectively expanded stem cells from human dental pulp in an initial culture using NSC media under xeno- and serum-free conditions. At the initial step of primary culture, human dental pulp was divided into two groups according to the culture media: 10% fetal bovine serum medium group (FBS group) and NSC culture medium group (NSC group). In the NSC group relative to the FBS group, the expression of NSC markers and the concentrations of leukemia inhibitory factor, nerve growth factor, and stem cell factor were higher, although their expression levels were lower than those of human fetal NSCs. The transplanted cells of the NSC group survived well within the normal brain and injured spinal cord of rats and expressed nestin and Sox2. Under the xeno- and serum-free conditions, autologous human dental pulp-derived stem cells might prove useful for clinical cell-based therapies to repair damaged neural tissues.

The c-kit signaling pathway is involved in the development of persistent pain

Protein kinase signal transduction pathways play critical roles in regulating nociception. Here we show that c-kit, a tyrosine kinase receptor, is expressed in lamina I and II layer of the dorsal horn. Moreover, the superficial c-kit(+) fibers originate from the dorsal root ganglion, and c-kit in lamina II inner layer comes from intrinsic expression of the spinal cord. Kit(W-v) mice, which contain a hypomorphic mutation, exhibited normal acute pain in most pain behavior tests. In the formalin test, the first phase was not affected, whereas the second phase pain response of Kit(W-v) mice was significantly reduced relative to wild-type littermates. Kit(W-v) mice also showed abnormal neuropathic pain, notably in the contralateral side of nerve injury. The expression and release of CGRP and substance P were not altered by the c-kit mutation. Together, these results implicate c-kit-mediated signal transduction in the development of persistent pain.

Characterization of c-kit (CD117) expression in human normal pituitary cells and pituitary adenomas

c-kit (CD117) is a tyrosine kinase receptor involved in the proliferation, differentiation, and secretory functions of various cells. In experimental animal models, c-kit has been detected in the pars intermedia of the normal pituitary gland and in alpha-melanocyte-stimulating-hormone-positive adenomas and it has been suggested that it plays a role in regulating adrenocorticotropic hormone (ACTH) secretion. To the best of our knowledge, the expression of c-kit in normal human pituitary cells and in pituitary adenomas has never been reported, so the possible biological role of this receptor in the control of pituitary hormone secretion remains unclear. The aim of this study was to evaluate the immunohistochemical expression of c-kit in normal human pituitary glands and in a series of 62 well-characterized pituitary adenomas. In normal adenohypophyses, several cells, mainly located in the central mucoid wedge, showed a c-kit immunoreactivity (IR). Double label immunostaining procedures showed that the c-kit-IR cells corresponded to ACTH cells. Out of 62 adenomas, 15 (24%) were c-kit-IR, including 7/16 (44%) ACTH cell, 3/7 (42%) null cell, 4/11 (36%) alpha-subunit cell, and 1/11 (10%) follicle-stimulating hormone-luteinizing hormone cell adenomas. By contrast, all ten prolactin cell and seven growth hormone cell adenomas were c-kit negative. These data suggest that, in normal conditions, c-kit may be involved in the pituitary-adrenal axis regulation.

Stem cell factor stimulates neurogenesis in vitro and in vivo

Cerebral ischemia stimulates neurogenesis in proliferative zones of the rodent forebrain. To identify the signaling factors involved, cerebral cortical cultures prepared from embryonic mouse brains were deprived of oxygen. Hypoxia increased bromodeoxyuridine (BrdU) incorporation into cells that expressed proliferation markers and immature neuronal markers and that lacked evidence of DNA damage or caspase-3 activation. Hypoxia-conditioned medium and stem cell factor (SCF), which was present in hypoxia-conditioned medium at increased levels, also stimulated BrdU incorporation into normoxic cultures. The SCF receptor, c-kit, was expressed in neuronal cultures and in neuroproliferative zones of the adult rat brain, and in vivo administration of SCF increased BrdU labeling of immature neurons in these regions. Cerebral hypoxia and ischemia may stimulate neurogenesis through trophic factors, including SCF.

Effects of Kit Ligand and anti-Kit antibody on growth of cultured mouse preantral follicles

Paracrine regulations between the oocyte and granulosa cells are likely to be key regulators of early folliculogenesis. Evidence obtained from genetic mutants as well as in vivo experiments suggest that Kit and Kit Ligand (KL) may regulate early follicular morphogenesis and function. In this study, we used in vitro culture of intact mouse follicles to confirm and extend these findings. Two concentrations of Kit Ligand (20 and 50 ng/ml) or an antibody blocking the Kit-Kit Ligand interactions (SC1494) were added to preantral follicles grown individually for 12 days and which were finally triggered to ovulate. Effects on follicle and oocyte survival, granulosa cell function (antrum formation, cell numbers, steroidogenesis), and oocyte function (growth, survival, nuclear and/or cytoplasmic maturation) were then analyzed. In optimal culture conditions (presence of 5% fetal calf serum), 50 ng/ml of KL significantly improved cytoplasmic maturation of the oocyte and increased follicular testosterone output, but other parameters were not altered. In serum-free culture conditions, KL was mitogenic for granulosa cells at 50 ng/ml, but could not induce antrum formation and no differences were observed between control and treated groups for steroidogenesis or oocyte growth. Blockade of Kit-Kit Ligand interactions by addition of a blocking antibody decreased oocyte survival 6-9 days after addition of the antibody, but did not upset granulosa cell proliferation. Antrum formation was, however, strongly inhibited. In addition, the blocking antibody markedly reduced aromatase activity of granulosa cells. We conclude that Kit/KL interactions are important for antrum formation and follicular steroidogenesis and regulate survival and cytoplasmic maturation of the oocyte.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.