Questions and (some) answers on reactive astrocytes

• Published in: Glia Vol. 67; no. 12; pp. 2221 - 2247
• Main Authors: Escartin, Carole, Guillemaud, Océane, Carrillo‐de Sauvage, Maria‐Angeles
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.12.2019; Wiley Subscription Services, Inc; Wiley
• Subjects: Animals; Astrocytes; Astrocytes - metabolism; Astrocytes - pathology; astrogliosis; Brain - metabolism; Brain - pathology; brain diseases; Central nervous system; Central Nervous System Diseases - metabolism; Central Nervous System Diseases - pathology; Gene expression; Gliosis; Gliosis - metabolism; Gliosis - pathology; Homeostasis; Humans; Life Sciences; Neurobiology; Neurons and Cognition; neuron–glia interactions; reactive astrocytes; Researchers; Synapses; Synaptic transmission; Synaptogenesis; neuron-glia interactions; astrogliosis; reactive astrocytes; brain diseases; animal models; Reactive astrocytes
• ISSN: 0894-1491; 1098-1136; 1098-1136
• DOI: 10.1002/glia.23687

Astrocytes are key cellular partners for neurons in the central nervous system. Astrocytes react to virtually all types of pathological alterations in brain homeostasis by significant morphological and molecular changes. This response was classically viewed as stereotypical and is called astrogliosis or astrocyte reactivity. It was long considered as a nonspecific, secondary reaction to pathological conditions, offering no clues on disease‐causing mechanisms and with little therapeutic value. However, many studies over the last 30 years have underlined the crucial and active roles played by astrocytes in physiology, ranging from metabolic support, synapse maturation, and pruning to fine regulation of synaptic transmission. This prompted researchers to explore how these new astrocyte functions were changed in disease, and they reported alterations in many of them (sometimes beneficial, mostly deleterious). More recently, cell‐specific transcriptomics revealed that astrocytes undergo massive changes in gene expression when they become reactive. This observation further stressed that reactive astrocytes may be very different from normal, nonreactive astrocytes and could influence disease outcomes. To make the picture even more complex, both normal and reactive astrocytes were shown to be molecularly and functionally heterogeneous. Very little is known about the specific roles that each subtype of reactive astrocytes may play in different disease contexts. In this review, we have interrogated researchers in the field to identify and discuss points of consensus and controversies about reactive astrocytes, starting with their very name. We then present the emerging knowledge on these cells and future challenges in this field. Main Points Astrocytes react to brain homeostasis alteration by morphological and molecular changes. This response is complex, heterogeneous and subject to controversies. New tools, models and concepts will help better understand this widespread reaction.