Titolo della tesi: Strain-specific response of astrocytes to prion infection
Prion diseases are fatal neurodegenerative diseases affecting both human and animals. The conformational conversion of host-encoded prion protein PrPC into an abnormal misfolded isoform called PrPSc is the key event in prion diseases pathology. Histologically, prion diseases are characterized by PrPSc deposition, spongiosis, neuronal loss and gliosis. Despite PrPSc is the only agent responsible for prion diseases, prions exist as different strains. The experimental infection of animal models is currently the gold standard tool for prion strain typing. In particular, each strain is described by the specific pathological change and biochemical properties exhibited in the experimentally infected animals at the terminal stage of the disease. Importantly, analysis performed in prion-infected mice over the course of disease have revealed dramatic aberrations of glia-enriched genes coinciding with the onset of clinical signs, suggesting a pivotal role of glial cells during the pathogenesis. Historically, most of studies have been addressed mainly on the microglial activation, while less attention has been paid to astrocytes involvement.
The present work focused on the astrocytes activation during prion diseases; in particular, we deepened the strain-related astrocytes response in experimental conditions. More specifically, we investigated how astrocytes react to different prion strains, and their relationship with PrPSc deposits.
Taking advantage of the availability of several prion strains adapted to bank vole model, we investigated the astrocytes response in vole-adapted strains isolated from human and animals characterized by different biochemical properties and survival times. Human strains were isolated from patients affected by sCJD-VV2, sCJD-MV1, sCJD-MM2T and GSS-F198S. Animal strains were isolated from one sheep affected by classic scrapie and one CWD-affected moose. After selection of vole-adapted strains, our study counted two different phases. Firstly, we studied the neuropathological changes of every single strain with different methods to determine the presence of specific features and to discriminate the strains, i.e. the strain-specific phenotype. Secondly, we investigated astrocyte response in selected strains and their relationship with PrPSc deposits.
Starting from the neuropathological characterization, we identified a commonly affected area in all strains to perform a comparative analysis of strain-associated astrocytes activation. Surprisingly, reactive astrocytes in mediodorsal thalamic nucleus exhibited strain-related morphological features. Importantly, by morphometric analysis, selected strains were clustered into three different groups.
To deepen the strain-related response of astrocytes, we studied the relationship between reactive astrocytes and PrPSc deposition. Only four out six strains showed intra-astrocytic deposits, despite all strains showed a prominent astrogliosis. Interestingly, the two strains lacking intra-astrocytic PrPSc deposition were clustered together based on the cellular area size. With the aim to test the relationship between astrocytes response and biochemical properties of strain, we selected an addition strain, TgL1-strain, characterized by biochemical properties similar to the GSS-F198S strain. Though isolated from two distinct species, namely humans and mice, these vole-adapted strains shared similar neuropathological signature and exhibited similar astrocytes response.
In conclusion, our results demonstrated that reactive astrocytes in prion diseases developed strain-associated morphological features. The PrPSc biochemical properties of strain seem to contribute to the triggering of astrocytes strain-dependent activation. Analysis of additional strains will be useful to confirm this relationship.
Further studies, such as analysis of neuro-inflammatory response or investigation into reactive astrocyte markers expression, may elucidate the strain-dependent involvement of astrocytes.