A Role for Thrombospondin-1 Deficits in Astrocyte- Mediated Spine and Synaptic Pathology in Down’s Syndrome Octavio Garcia, Maria Torres, Pablo Helguera, Pinar Coskun, Jorge Busciglio* Department of Neurobiology and Behavior, Institute for Memory Impairments and Neurological Disorders (iMIND), Center for the Neurobiology of Learning and Memory (CNLM), University of California Irvine, Irvine, California, United States of America Abstract Background: Down’s syndrome (DS) is the most common genetic cause of mental retardation. Reduced number and aberrant architecture of dendritic spines are common features of DS neuropathology. However, the mechanisms involved in DS spine alterations are not known. In addition to a relevant role in synapse formation and maintenance, astrocytes can regulate spine dynamics by releasing soluble factors or by physical contact with neurons. We have previously shown impaired mitochondrial function in DS astrocytes leading to metabolic alterations in protein processing and secretion. In this study, we investigated whether deficits in astrocyte function contribute to DS spine pathology. Methodology/Principal Findings: Using a human astrocyte/rat hippocampal neuron coculture, we found that DS astrocytes are directly involved in the development of spine malformations and reduced synaptic density. We also show that thrombospondin 1 (TSP-1), an astrocyte-secreted protein, possesses a potent modulatory effect on spine number and morphology, and that both DS brains and DS astrocytes exhibit marked deficits in TSP-1 protein expression. Depletion of TSP-1 from normal astrocytes resulted in dramatic changes in spine morphology, while restoration of TSP-1 levels prevented DS astrocyte-mediated spine and synaptic alterations. Astrocyte cultures derived from TSP-1 KO mice exhibited similar deficits to support spine formation and structure than DS astrocytes. Conclusions/Significance: These results indicate that human astrocytes promote spine and synapse formation, identify astrocyte dysfunction as a significant factor of spine and synaptic pathology in the DS brain, and provide a mechanistic rationale for the exploration of TSP-1-based therapies to treat spine and synaptic pathology in DS and other neurological conditions. Citation: Garcia O, Torres M, Helguera P, Coskun P, Busciglio J (2010) A Role for Thrombospondin-1 Deficits in Astrocyte-Mediated Spine and Synaptic Pathology in Down’s Syndrome. PLoS ONE 5(12): e14200. doi:10.1371/journal.pone.0014200 Editor: Mel B. Feany, Brigham and Women’s Hospital, Harvard Medical School, United States of America Received July 2, 2010; Accepted November 15, 2010; Published December 2, 2010 Copyright: ß 2010 Garcia et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by grants from The Larry L. Hillblom Foundation and the National Institutes of Health (grant no. HD38466, and Alzheimers Disease Research Center grant no. AG16573). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: jbuscigl@uci.edu Introduction Down’s syndrome (DS) or the triplication of chromosome 21 (trisomy 21) is the most common genetic cause of mental retardation. The cognitive deficits in patients with DS have been associated with structural changes in the architecture and alterations in the number of dendritic spines [1]. Morphological abnormalities such as unusually long spines, shorter spines, and reduced number of spines have been documented in the cortex of DS fetuses and newborns [2,3]. Similar alterations were observed in the hippocampal formation, and additional reductions in spine number in adult DS patients have been linked to the development of Alzheimer’s disease (AD) pathology [4,5]. Spine pathology is also present in the Ts65Dn mouse model of DS, which shows decreased spine and synaptic density, and aberrant spine morphology including enlarged spines, irregular spine heads, and globular spine shapes [6–8]. Since dendritic spines are the primary sites of excitatory synapses, defects in spine structure and function can result in synaptic and circuit alterations leading to cognitive impairment and the progression of AD pathology in DS patients [9]. Unfortunately, there is little information available on the cellular and molecular mechanisms involved in DS spine malformation. In recent years, a number of studies indicate that astrocytes regulate the stability, dynamics and maturation of dendritic spines [10–13]. In addition, astrocytes participate in the regulation of synaptic plasticity and synaptic transmission [14–18]. Astrocytes modulate the establishment and maintenance of synaptic contacts through the release of soluble factors such as cholesterol [19] or thrombospondins [20], or by direct physical interaction with neuronal cells [10–13,21]. Our previous research indicates the presence of mitochondrial dysfunction and energy deficits in DS astrocytes leading to abnormal amyloid precursor protein (APP) processing and secretion, and to intracellular accumulation of amyloid b (Ab) [22]. To investigate the role of astrocytes in DS spine pathology, we established a coculture system in which rat PLoS ONE | www.plosone.org 1 December 2010 | Volume 5 | Issue 12 | e14200