The underlying conversion mechanism of PrPC into PrPSc is poorly understood and is further complicated by the existence of several different prion strains characterized by distinct tertiary and quaternary structures as well as different clinical patterns [1]. Several hypotheses exist about the contribution of unknown molecules other than PrP to prion propagation.

To address this issue, several animal studies have investigated the host response to prion infection of different origins and strains. In this context, analyses of gene expression alterations that occur in prion-infected animals represents a powerful tool that may contribute to unraveling the molecular basis of prion diseases and therefore reveal novel potential targets for diagnosis and therapeutics.

The differential gene expression after prion infection has been extensively explored (reviewed in [2,3]); however, most of the studies involved animal models such as mice, sheep and cattle, all distantly related to humans.

Therefore, we performed a large-scale gene expression analysis of brains from BSE-infected cynomolgus macaques (Macaca fascicularis), which are known to be an excellent model for studying human acquired prion diseases.

The results obtained with the Affymetrix® microarray platform have shown hundreds of differentially expressed transcripts, some associated to known functions in the frontal cortex [4]. These genes belong to various pathways including oxygen homeostasis, lipid metabolism and inflammation response. Further validation of differentially expressed transcripts, using RT-qPCR, showed significant up-regulation of SERPINA3 and down-regulation of both HBB and HBA2 transcripts) [4].

In order to confirm these dysregulations, we performed RT-qPCR on 128 suitable frontal cortex samples, from prion-infected patients (variant Creutzfeldt-Jakob disease (vCJD) n = 20, iatrogenic CJD (iCJD) n = 11, sporadic CJD (sCJD) n = 23, familial CJD (gCJD) n = 17, fatal familial insomnia (FFI) n = 9, Gerstmann–Sträussler–Scheinker syndrome (GSS) n = 4), patients with Alzheimer disease (AD, n = 14) and age-matched controls (n = 30) [5,6]. 

We reported SERPINA3 to be strongly up-regulated in the brain of all human prion diseases analyzed, with only a mild up-regulation in AD. Western Blot and neuropathological analysis of frontal cortex samples from affected patients confirmed transcriptomics data [5].

Concerning hemoglobin expression in the brain of neurodegenerative affted patients, we firstly decided to include the expression level of an erithrocye marker (ALAS2) in order to normalize the gene expression of HBB and HBA1/2 for each single sample on its specific blood content. While in genetic prion diseases and sporadic CJD groups HBB and HBA1/2 expression levels did not show any dysregulation, in AD patients both hemoglobin transcripts were strongly down-regulated. Immunofluorescence and confocal microscopy showed reduced hemoglobin immunoreactivity in neurons of AD and sCJD compared to control frontal cortex [6].

Taken together these results highlighted the importance of transcriptomic analyses as unbiased starting approach to identify disease-related genes (and proteins) and potential drug targets.

1. Legname G., et al., Continuum of prion protein structures enciphers a multitude of prion isolate-specified phenotypes. Proc Natl Acad Sci U S A, 2006. 103(50): p. 19105-10

2. Benetti F., Gustincich S., and Legname G., Gene expression profiling and therapeutic interventions in neurodegenerative diseases: a comprehensive study on potentiality and limits. Expert Opin Drug Discov, 2012. 7(3): p. 245-59.

3. Silvia Vanni, Chapter Nineteen - Omics of Prion Diseases, Editor(s): Giuseppe Legname, Silvia Vanni, Progress in Molecular Biology and Translational Science, Academic Press, Volume 150, 2017, Pages 409-431, ISSN 1877-1173, ISBN 9780128112267.

4. Barbisin M., et al., Gene expression profiling of brains from bovine spongiform encephalopathy (BSE)-infected cynomolgus macaques. BMC Genomics, 2014. 15: p. 434.

5. Vanni S., et al., Differentialoverexpression of SERPINA3 in human prion diseases. Sci. Rep. 7:15637 (2017)

6. Vanni S., et al., Hemoglobin mRNA Changes in the Frontal Cortex of Patients with Neurodegenerative Diseases. Frontiers in neuroscience12, 8 (2018).