Blood test closer for mad cow disease, Alzheimers and Parkinson's
by: Pia Akerman From:The Australian
September 12, 201210:51AM
BLOOD tests to diagnose Alzheimers disease, Parkinson's and the human form of mad cow disease could be closer thanks to new Australian research.
Research by University of Melbourne scientists, published in the Nucleic Acids Research journal this week, has identified specific particles (exosomes) released by cells infected with prions, the pathogen that causes diseases such as human variant Creutzfeldt-Jakob disease.
It raises the possibility of a diagnostic blood test identifying the exosomes in the blood stream.
Thousands of Australians are currently banned from donating blood because they lived in the UK when mad cow disease was present in local beef and there is no easy test to identify the risk.
Since 2004 a small number of British residents have been diagnosed with vCJD transmitted through blood transfusion.
University of Melbourne associate professor Andrew Hill, who worked on the research, said further testing was needed.
He said while Alzheimer's and Parkinson's were not transmissible like prion diseases such as vCJD, they similarly released the exosome particles.
"Our thinking is that they might too have a unique signature on them that we could potentially pick up in blood as well," he said.
"Obviously these brain diseases are hard to diagnose because you need very extensive imaging tests to see what's going on inside the brain."
The Red Cross has previously said its ban on blood donations from people who lived in the UK between 1980 and 1996 for more than six months, or received blood transfusions there, would remain until there was a reliable blood screening test for vCJD.
Nucleic Acids Research Advance Access published September 10, 2012
Nucleic Acids Research, 2012, 1–13 doi:10.1093/nar/gks832
Small RNA deep sequencing reveals a distinct miRNA signature released in exosomes from prion-infected neuronal cells
Shayne A. Bellingham1,2, Bradley M. Coleman1,2 and Andrew F. Hill1,2,3,*
1Department of Biochemistry and Molecular Biology,
2Bio21 Molecular Science and Biotechnology Institute and
3Mental Health Research Institute, The University of Melbourne, Parkville, Victoria 3010, Australia
Received December 8, 2011; Revised and Accepted August 9, 2012
Prion diseases are transmissible neurodegenerative disorders affecting both humans and animals. The cellular prion protein, PrPC, and the abnormal infectious form, PrPSc, are found associated with exosomes, which are small 50–130nm vesicles released from cells. Exosomes also contain microRNAs (miRNAs), a class of non-coding RNA, and have been utilized to identify miRNA signatures for diagnosis of disease. While some miRNAs are deregulated in prion-infected brain tissue, the role of miRNA in circulating exosomes released during prion disease is unknown. Here, we investigated the miRNA profile in exosomes released from prion-infected neuronal cells. We performed the first small RNA deep sequencing study of exosomes and demonstrated that neuronal exosomes contain a diverse range of RNA species including retroviral RNA repeat regions, messenger RNA fragments, transfer RNA fragments, noncoding RNA, small nuclear RNA, small nucleolar RNA, small cytoplasmic RNA, silencing RNA as well as known and novel candidate miRNA. Significantly, we show that exosomes released by prion-infected neuronal cells have increased let-7b, let-7i, miR-128a, miR-21, miR-222, miR-29b, miR-342-3p and miR-424 levels with decreased miR-146 a levels compared to non-infected exosomes. Overall, these results demonstrate that circulating exosomes released during prion infection have a distinct miRNA signature that can be utilized for diagnosis and understanding pathogenic mechanisms in prion disease.
While this hypothesis remains to be tested, these observations leave open the possibility that miRNAs are packaged into exosomes as a result of PrPC binding AGO1 and AGO2 promoting formation of miRISCs on the MVB, which functions as checkpoint for scanning mRNAs. Therefore selecting AGO-bound complementary mRNA:miRNAs that are to be repressed, while non-complementary miRNAs are packaged into ILVs along with PrPC and released with exosomes. Whether misfolding of PrPC into PrPSc during prion disease infection alters its ability to bind to Argonaute proteins, modulates the function of miRISC on the MVB and subsequent release of miRNA in exosomes during prion diseases certainly deserves investigation. Given that, we have identified significant changes in particular miRNA species released in association with exosomes from prion-infected cells, its plausible to suggest that miRNAs are selectively packaged as a direct result of PrPC and PrPSc and its influence on the miRNA biogenesis pathway. In summary, our results strongly support the hypothesis that exosomes released from prion-infected neuronal cells have a distinct miRNA signature that may be utilized for the identification of prion infection. This signature comprises significant increases in let-7 b, let-7i, miR-128 a, miR-21, miR-222, miR-29 b, miR-342-3 p and miR-424 with decreased miR-146 a detection and agrees to some extent to previously reported miRNA changes detected in brains of terminally infected mouse and primate models of prion disease, and sporadic CJD samples (17,18). Evaluation of our exosomal miRNA signature in circulating exosomes derived from clinical plasma samples from sporadic and variant forms of human prion disease and in animal models infected with different prion strains will be the subject of our further studies. Importantly, it has been shown the miRNAs deregulated in prion-infected exosomes identified in this study have also been detected in circulating exosomes isolated from human serum samples (14), and that neither have currently been detected in disease-associated exosomes in the current literature and a search of ExoCarta database (58), suggesting that this miRNA signature has significant and specific diagnostic potential. However, it should be noted that our study also identified other ncRNAs and mRNA fragments (Supplementary Figure S1) that may also be deregulated in exosomes released from prioninfected neuronal cells. Furthermore, it has been identified that extracellular miRNA released from cells into plasma can associate in two populations, both dependent and independent of exosomes either bound to AGO2 (59–61) or high-density lipoproteins (62). Therefore, targeted exosomal purification strategies for enrichment of circulating miRNA biomarkers may be required to increase biomarker sensitivity (14,15,23). This research also has potential diagnostic implications for other neurodegenerative diseases in which exosomes have been identified to play a role including Alzheimer’s disease (63– 65), amyotrophic lateral sclerosis (66) and Parkinson’s disease (67).
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Proposal ID: 29403