Abstract
Under normal conditions, astrocytes perform a number of important physiological functions centered around neuronal support and synapse maintenance. In neurodegenerative diseases including Alzheimer’s, Parkinson’s and prion diseases, astrocytes acquire reactive phenotypes, which are sustained throughout the disease progression. It is not known whether in the reactive states associated with prion diseases, astrocytes lose their ability to perform physiological functions and whether the reactive states are neurotoxic or, on the contrary, neuroprotective. The current work addresses these questions by testing the effects of reactive astrocytes isolated from prion-infected C57BL/6J mice on primary neuronal cultures. We found that astrocytes isolated at the clinical stage of the disease exhibited reactive, pro-inflammatory phenotype, which also showed downregulation of genes involved in neurogenic and synaptogenic functions. In astrocyte-neuron co-cultures, astrocytes from prion-infected animals impaired neuronal growth, dendritic spine development and synapse maturation. Toward examining the role of factors secreted by reactive astrocytes, astrocyte-conditioned media was found to have detrimental effects on neuronal viability and synaptogenic functions via impairing synapse integrity, and by reducing spine size and density. Reactive microglia isolated from prion-infected animals were found to induce phenotypic changes in primary astrocytes reminiscent to those observed in prion-infected mice. In particular, astrocytes cultured with reactive microglia-conditioned media displayed hypertrophic morphology and a downregulation of genes involved in neurogenic and synaptogenic functions. In summary, the current study provided experimental support toward the non-cell autonomous mechanisms behind neurotoxicity in prion diseases and demonstrated that the astrocyte reactive phenotype associated with prion diseases is synaptotoxic.
Highlights
Chronic neuroinflammation is a major feature of neurodegenerative diseases including Alzheimer’s, Parkinson’s and prion diseases [1]
Isolation and purification of primary astrocytes from adult mouse brains To examine the pathophysiological role of astrocytes in prion diseases, first we optimized a protocol for isolation and culturing of primary astrocytes from adult mouse brains (220–300 day old C57Bl/6J mice)
Mouse adapted prion strain (22L)‐derived reactive microglia induce a pro‐inflammatory state in primary astrocytes For testing whether factors secreted by Primary microglia cultures derived from 22L animals (22L-primary microglia cultures (PMCs)) dictate astrocyte phenotype, we examined the effect of microglia conditioned medium (MCM) on primary cortical astrocytes isolated from adult C57Bl/6J mice
Summary
Chronic neuroinflammation is a major feature of neurodegenerative diseases including Alzheimer’s, Parkinson’s and prion diseases [1]. Transgenic mouse models of human neurodegenerative diseases advanced our understanding of diversity of glial reactive phenotypes [4,5,6]. The question of whether animal models faithfully recapitulate chronic neuroinflammation associated with diseases in humans has been raised on multiple occasions [7,8,9]. Unlike modeling of most neurodegenerative diseases that rely on transgenic animals, transmissible bona fide prion diseases can be induced in wild-type or inbred animals upon infection with the disease-associated form of the prion protein, or PrPSc [10]. The diversity of disease phenotypes is attributed to the structural diversity of PrPSc states referred to as prion strains [12].
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