ABSTRACT
Adult neural stem cells (NSC) proliferate and differentiate depending on the composition of the cellular and molecular niche in which they are immersed. Until recently, microglial cells have been ignored as part of the neurogenic niche. We studied the dynamics of NSC proliferation and differentiation in the dentate gyrus of the hippocampus (DG) and characterized the changes of the neurogenic niche in adrenalectomized animals (ADX). At the cellular level, we found increased NSC proliferation and neurogenesis in the ADX animals. In addition, a morphologically distinct subpopulation of NSC (Nestin+/GFAP-) with increased proliferating profile was detected. Interestingly, the number of microglial cells at stages 2 and 3 of activation correlated with increased neurogenesis (r2 = 0.999) and the number of Nestin-positive cells (r2 = 0.96). At the molecular level, transforming growth factor beta (TGF-beta) mRNA levels were increased 10-fold in ADX animals. Interestingly, TGF-beta levels correlated with the amount of neurogenesis detected (r2 = 0.99) and the number of stage 2 and 3 microglial cells (r2 = 0.94). Furthermore, blockade of TGF-beta biological activity by administration of an anti-TGF-beta type II receptor antibody diminished the percentage of 5-bromo-2'-deoxyuridine (BrdU)/PSA-NCAM-positive cells in vivo. Moreover, TGF-beta was able to promote neurogenesis in NSC primary cultures. This work supports the idea that activated microglial cells are not pro- or anti-neurogenic per se, but the balance between pro- and anti-inflammatory secreted molecules influences the final effect of this activation. Importantly, we identified an anti-inflammatory cytokine, TGF-beta, with neurogenic potential in the adult brain.
Subject(s)
Dentate Gyrus/cytology , Microglia/physiology , Neurons/physiology , Stem Cells/physiology , Transforming Growth Factor beta/metabolism , Adrenalectomy/methods , Animals , Antibodies/pharmacology , Bromodeoxyuridine/metabolism , Cell Count/methods , Cell Proliferation/drug effects , Cells, Cultured , Diagnostic Imaging/methods , Glial Fibrillary Acidic Protein/metabolism , Immunohistochemistry/methods , Intermediate Filament Proteins/metabolism , Male , Microglia/drug effects , Nerve Tissue Proteins/metabolism , Nestin , Neural Cell Adhesion Molecule L1/metabolism , Neurons/classification , Neurons/drug effects , Proteoglycans/immunology , RNA, Messenger/biosynthesis , Radioimmunoassay/methods , Rats , Rats, Wistar , Receptors, Transforming Growth Factor beta/immunology , Reverse Transcriptase Polymerase Chain Reaction/methods , Sialic Acids/metabolism , Stem Cells/drug effects , Time Factors , Transforming Growth Factor beta/genetics , Transforming Growth Factor beta/pharmacology , Tubulin/metabolismABSTRACT
Leprosy is an infectious disease with two polar forms, tuberculoid leprosy (TT) and lepromatous leprosy (LL), that are characterized by strong cell-mediated immunity (CMI) and CMI anergy, respectively. Transforming growth factor-beta (TGF-beta) belongs to a family of pleiotropic cytokines (TGF-beta1, TGF-beta2 and TGF-beta3) that participate in the control of cell differentiation and proliferation, as well as tissue repair. This cytokine family is unique because it suppresses CMI. In this study, we compared the expression of the three TGF-beta isoforms and their receptors in skin biopsies from LL and TT patients (LL = 20; TT = 20) using immunohistochemistry and automated morphometry. The percentage of cells immunostained for the three TGF-beta isoforms and cells positive for the three TGF-beta receptors in the inflammatory infiltrate located in the papillary dermis, reticular dermis and periadnexal tissue were significantly higher in LL than that in TT, with macrophages being the most common and strongest immunoreactive cells. Some lymphocytes, fibroblasts, keratinocytes and epithelial cells from sweat glands and hair roots were also positive. In situ reverse-transcription polymerase chain reaction corroborated the capacity of these cells to synthesize TGF-beta1 and TGF-beta receptor 2. This high expression of TGF-beta isoforms and their receptors could contribute to CMI anergy and other clinical characteristic features of leprosy, like skin atrophy.