Brain-Derived Extracellular Vesicles are Highly Enriched in the Prion Protein and Its C1 Fragment: Relevance for Cellular Uptake and Implications in Stroke

Abstract

Extracellular vesicles (EVs) are important means of intercellular communication and a potent tool for regenerative therapy. In ischemic stroke, transient blockage of a brain artery leads to a lack of glucose and oxygen in the affected brain tissue, provoking neuronal death by necrosis in the core of the ischemic region. The fate of neurons in the surrounding penumbra depends on the stimuli, including EVs, received during the following hours. A detailed characterization of such stimuli is crucial not only for understanding stroke pathophysiology but also for new therapeutic interventions.In the present study, we characterize the EVs in mouse brain under physiological conditions and 24h after induction of transient ischemia in mice. We show that, in steady-state conditions, microglia are the main source of small EVs (sEVs) whereas after ischemia, the main EV population originates from astrocytes. Moreover, sEVs presented high amounts of the prion protein (PrP) which were increased after stroke. Conspicuously, sEVs were particularly enriched in a truncated PrP fragment (PrP-C1). Because of similarities between PrP-C1 and certain viral surface proteins, we studied the cellular uptake of brain-derived sEVs from mice lacking (PrP-KO) or containing PrP (WT). We show that PrP-KO-EVs are rapidly taken up by neurons and colocalize with lysosomes. Although eventually WT-EVs are also found in lysosomes, the amount taken up by neurons is significantly higher for PrP-KO-EVs. Likewise, microglia and astrocytes were also engulfing PrP-KO-sEVs more efficiently than WT-sEVs.Our results provide information on the relative contribution of brain cell types to the sEV pool in mice and indicate that increased release of sEVs by astrocytes together with elevated levels of PrP in sEVs may play a role in intercellular communication at early stages after stroke. In addition, amounts of PrP (and probably PrP-C1) in brain sEVs seem to contribute to their cellular uptake.

A New Take on Prion Protein Dynamics in Cellular Trafficking

“…PrP C is enriched in exosomes derived from a variety of cell types, including neural cells, and is also found in cerebral spinal fluid [ 74 ] and plasma [ 75 ]. Recent studies demonstrated that elevated levels of PrP C in extracellular vesicles (EVs)/exosomes may play a role in intercellular signaling and it is implicated in early stages after stroke [ 76 ]. Interestingly, the levels of PrP C in plasma exosomes of patients with Parkinson’s disease (PD) was directly correlated with cognitive impairment, suggesting a role for exosomal-PrP C in the prognosis of PD [ 77 ].…”

Show Me Your Friends and I Tell You Who You Are: The Many Facets of Prion Protein in Stroke

“…PrPC is enriched in EVs [ 230 , 231 , 232 ] but not much is known about its physiological functions therein. We recently found that EVs purified from mouse brain are highly enriched in PrPC and its proteolytic C1 fragment (see paragraph above) [ 232 ]. PrP levels were further increased in EVs isolated from mice subjected to tMCAO (40 min) at 24 h after reperfusion.…”