Long-term monitoring of chronic demyelination and remyelination in a rat ischemic stroke model using macromolecular proton fraction mapping

Abstract

Remyelination is a key process enabling post-stroke brain tissue recovery and plasticity. This study aimed to explore the feasibility of demyelination and remyelination monitoring in experimental stroke from the acute to chronic stage using an emerging myelin imaging biomarker, macromolecular proton fraction (MPF). After stroke induction by transient middle cerebral artery occlusion, rats underwent repeated MRI examinations during 85 days after surgery with histological endpoints for the animal subgroups on the 7th, 21st, 56th, and 85th days. MPF maps revealed two sub-regions within the infarct characterized by distinct temporal profiles exhibiting either a persistent decrease by 30%–40% or a transient decrease followed by return to nearly normal values after one month of observation. Myelin histology confirmed that these sub-regions had nearly similar extent of demyelination in the sub-acute phase and then demonstrated either chronic demyelination or remyelination. The remyelination zones also exhibited active axonal regrowth, reconstitution of compact fiber bundles, and proliferation of neuronal and oligodendroglial precursors. The demyelination zones showed more extensive astrogliosis from the 21st day endpoint. Both sub-regions had substantially depleted neuronal population over all endpoints. These results histologically validate MPF mapping as a novel approach for quantitative assessment of myelin damage and repair in ischemic stroke.

Macromolecular Proton Fraction as a Myelin Biomarker: Principles, Validation, and Applications

“…The loss of axons and neurons in ischemic stroke did not affect MPF ( Khodanovich et al, 2018 ). MPF in the ischemic infarct was also found to be insensitive to microglial ( Khodanovich et al, 2018 ) and astroglial ( Khodanovich et al, 2021 ) proliferation, which represent pathological hallmarks of sub-acute and chronic stroke lesions. At the same time, due to dilution of the macromolecular content, MPF is affected by edema ( Stanisz et al, 2004 ; Harkins et al, 2013 ; Khodanovich et al, 2018 ), which may cause up to 10–15% overestimation of myelin loss by MPF in acute stroke ( Khodanovich et al, 2018 ).…”

“…Macromolecular proton fraction measurements were compared with histological myelin assessment in a variety of animal models including normal animal brain ( Underhill et al, 2011 ; Khodanovich et al, 2017 ) and spinal cord ( Dula et al, 2010 ), cuprizone-induced demyelination in mice ( Thiessen et al, 2013 ; Turati et al, 2015 ; Khodanovich et al, 2017 , 2019 ; Soustelle et al, 2019 , 2021 ), experimental autoimmune encephalomyelitis in rats ( Rausch et al, 2009 ), lipopolysaccharide-induced focal demyelination in rats ( Janve et al, 2013 ), hexachlorophene-induced intramyelinic edema in rats ( Harkins et al, 2013 ), genetic hypomyelination ( Ou et al, 2009a , b ; West et al, 2018 ) and hypermyelination ( West et al, 2018 ) in mice, ischemic stroke in rats ( Khodanovich et al, 2018 , 2021 ), spinal cord injury in primates ( Wang et al, 2016 , 2019 ; Wu et al, 2020 ), and demyelinated peripheral nerve ex vivo ( Odrobina et al, 2005 ; Ou et al, 2009a ). All studies reported qualitative correspondence of demyelinated anatomical zones with a reduced MPF and/or MPF reduction associated with demyelination relative to a control sample.…”

“…All studies reported qualitative correspondence of demyelinated anatomical zones with a reduced MPF and/or MPF reduction associated with demyelination relative to a control sample. When histology was quantitatively assessed, MPF demonstrated strong correlations with histological myelin markers characterized by correlation coefficients in a range 0.7–0.99 ( Underhill et al, 2011 ; Janve et al, 2013 ; Thiessen et al, 2013 ; Turati et al, 2015 ; Khodanovich et al, 2017 , 2018 , 2019 , 2021 ; West et al, 2018 ; Soustelle et al, 2019 , 2021 ).…”

“…An increase in MPF was correlated with re-myelination after withdrawal of cuprizone ( Turati et al, 2015 ; Khodanovich et al, 2019 ) and replicated restoration of oligodendrogenesis ( Khodanovich et al, 2019 ) in WM and GM of cuprizone-pretreated mice. In the stroke model, MPF showed a unique capability to identify local post-ischemic remyelination, which was unobservable with conventional imaging techniques ( Khodanovich et al, 2021 ).…”

Challenges and Practical Solutions to MRI and Histology Matching and Measurements Using Available ImageJ Software Tools

“…The main advantage of the ROIT method is its applicability in solving complicated cases, for example, when it is impossible to determine the boundaries of the ROI on the histological image and there is no initial information about the measured parameter within this region. Specific examples may include the assessment of cell death, inflammation, regeneration, and in animal studies of stroke [ 8 , 45 , 46 , 47 ].…”