Delivery of mitochondria-containing extracellular vesicles to the BBB for ischemic stroke therapy

ABSTRACT

Introduction

Ischemic stroke-induced mitochondrial dysfunction in brain endothelial cells (BECs) leads to breakdown of the blood–brain barrier (BBB) causing long-term neurological dysfunction. Restoration of mitochondrial function in injured BECs is a promising therapeutic strategy to alleviate stroke-induced damage. Mounting evidence demonstrate that selected subsets of cell-derived extracellular vehicles (EVs), such as exosomes (EXOs) and microvesicles (MVs), contain functional mitochondrial components. Therefore, development of BEC-derived mitochondria-containing EVs for delivery to the BBB will (1) alleviate mitochondrial dysfunction and limit long-term neurological dysfunction in ischemic stroke and (2) provide an alternative therapeutic option for treating numerous other diseases associated with mitochondrial dysfunction.

Area covered

This review will discuss (1) how EV subsets package different types of mitochondrial components during their biogenesis, (2) mechanisms of EV internalization and functional mitochondrial responses in the recipient cells, and (3) EV biodistribution and pharmacokinetics – key factors involved in the development of mitochondria-containing EVs as a novel BBB-targeted stroke therapy.

Expert opinion

Mitochondria-containing MVs have demonstrated therapeutic benefits in ischemic stroke and other pathologies associated with mitochondrial dysfunction. Delivery of MV mitochondria to the BBB is expected to protect the BBB integrity and neurovascular unit post-stroke. MV mitochondria quality control, characterization, mechanistic understanding of its effects in vivo, safety and efficacy in different preclinical models, large-scale production, and establishment of regulatory guidelines are foreseeable milestones to harness the clinical potential of MV mitochondria delivery.

KEYWORDS:

• Mitochondria
• extracellular vesicles
• exosomes
• microvesicles
• stroke
• BBB

Article highlights

• Ischemic stroke causes mitochondrial dysfunction and tight junction breakdown in brain endothelial cells that leads to long-term neurological damage post-stroke.

• Cell-derived extracellular vesicles (EVs), including exosomes (EXOs) and microvesicles (MVs), package mitochondrial content during their biogenesis.

• EXOs contain mtDNA and mitochondrial proteins whereas MVs contain functional mitochondria.

• EV-mediated transfer of mitochondrial components to recipient cells increases cellular bioenergetics, survival, mtDNA copy number, and modulates anti-inflammatory responses.

• Mitochondria-containing EVs show therapeutic benefits in various pathological conditions associated with mitochondrial dysfunction, including ischemic stroke.

Key abbreviations

ATP	=	Adenosine triphosphate
BBB	=	Blood-brain barrier
BEC	=	Brain endothelial cells
CSF	=	Cerebrospinal fluid
DAMPs	=	Damage-associated molecular patterns
ESCRT	=	Endosomal-sorting complex essential for transport
EVs	=	Extracellular vesicles
EXOs	=	Exosomes
IN	=	Intranasal
IV	=	Intravenous
MCAO	=	Middle cerebral artery occlusion
MDV	=	Mitochondria-derived vesicles
MSCs	=	Mesenchymal stem cells
mtDNA	=	mitochondrial DNA
MVs	=	Microvesicles
MVB	=	Multivesicular bodies
OGD	=	Oxygen-glucose deprivation
PEG	=	Poly(ethylene glycol)
ROS	=	Reactive oxygen species
TEM	=	Transmission electron microscopy
TJ	=	Tight junction

Declaration of interest

DS Manickam is a named inventor on a provisional patent application disclosing mitochondria-enriched EVs discussed here. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

The authors acknowledge start-up funds for the Manickam laboratory from Duquesne University and a [2018 Faculty Development Fund] (Office of Research, DU) to the PI for financial support.