Neurodegeneration and stem cells Flashcards
Aguayo et al 1982
Segment of sciatic nerve inserted close to cerebral cortex - CNS axons labelled close to the graft elongated in a remarkable fashion - glial environment characteristic of the PNS responsible for this
Confounded by the injury process inserted the graft into the brain - perform on a sham control
Davies et al 1999
Immunohistochemistry revealed significant ECM abundance around astro-glial scars - large amounts of the chondroitin sulfate proteoglycans CS-PGs
areas of high CS-PG concentration were areas most lacking axon regeneration first notion that CS-PG is inhibitory to neurite outgrowth.
Enzyme chondroitinase ABC, cleave CS-PG GAG side chains - reverse the inhibitory effect the ECM component can have in vivo
Bradbury et al 2002
ChABC treatment restored post-synaptic activity and promoted functional recovery of locomotor and proprioceptive behaviours in the lesioned rat dorsal column
Electrophysiological parameter of recovery is just one way of measuring - anatomical regeneration was limited, potentially due to other inhibitory properties of the glial scar impairing significant regrowth.
Study was limited by not publishing long term data - It would be important to investigate the influence of other inhibitory factors released by glial scars over time, (i.e Nogo and Myelin associated glycoprotein), which may have offset the benefits that ChABC has on creating a growth suiting environment.
Desestret et al 2013
Demonstrated that M2 macrophage administration at subacute stages after middle cerebral occlusion (MCAO) failed to improve stroke outcomes after 2 weeks
Although this study is inconclusive due to the lack of a dose-response curve and long-term endpoints, it raises several important concerns about M2 microglia/macrophage therapy.
What is the optimal route of administration? When should the cells be administered? Is CNS penetration essential for therapeutic effects?
Mikita et al 2011
EAE MS model
MRI macrophage tracking with USPIO nanoparticles and expression patterns of M1/M2 macrophages
M1/M2 equilibrium in blood promotes mild EAE
Imbalance towards M1 promotes relapsing EAE.
Administration of ex vivo activated M2 monocytes both suppressed ongoing severe EAE and increased immunomodulatory expression pattern in lesions
Blesch et al 2003
Implanted primary fibroblasts genetically modified to secrete GDNF
Axon density increased in grafts (measured using image analysis), schwann cell marker detected, SC migrated into grafts (density 6 fold higher in grafts containing GDNF than not)
However, similar to treatment with anti-inhibitory molecules NO significant functional recovery, as axons fail to re-establish connectivity.
Instead, remerging axons were observed in greatest density in areas of high GDNF concentration, in the centre of the graft, trapping them in situ.
Handarmin et al 2011
By incorporating a GF gradient within nanofibrous scaffolds, neurite outgrowth (distance elongated by axons) was raised by ~7%.
Li et al 2005
Histological analysis highlighted the pathway hypothesis, channels for axon regrowth
Cheah et al 2016
When alpha9beta1 tenascin binding integrin was expressed in DRG via an adenovirus vector twelve weeks after injury, axons grew from C6–7 level to above C1, covering a distance of more than 25 mm.
Behavioural and locomotor recovery was also observed in the animals suggesting not only neurite outgrowth, but reconnection.
Would be more limited in humans - due to greater distances
It is important to note however, that in the presence of inhibitory external molecules (Nogo, CSPGs) more modest effects.
YET when integrins were combined with kindlins, integrin activators, and the inhibitory effects of the environment could be diminished without direct specific targeting of inhibitory molecules.
Cho et al 2017
Histone acetyltransferase (HAT) p300/CBP-associated factor (PCAF) is upregulated post injury by ERK signalling.
PCAF goes on to modify histones close to the promoters of RAGs, to upregulate these genes.
PCAF overexpression in spinal cord axons improves regeneration
Olstorn et al 2011
Adult neural progenitor cells were collected from resections for epilepsy - seven days after ischemia in the rat, cells were pre-differentiated (factor treated) transplanted into hippocampus, after 4/10 weeks, brains were analysed with immunohistochemistry
Cells that were treated expressed neural markers at a much earlier stage (4 weeks post grafting). Migrated preferentially into ischemic lesion
HOWEVER – cells taken from epilepsy resections – perhaps pathological cells are not the best contributors, highlights the challenges of performing these experiments when cells are so challenging to find
Presence of cells found at 4 and 10 weeks - still limited evidence for any functional benefit to the cells
Yang et al 2011
nestin-GFP reporter (so stem cells labelled with nestin express GFP)
Lack of ApoE increased proliferation of early NPCs within the DG - proliferation assay in-vivo used BrDu - label dividing cells
Perhaps lengthening of the S phase not increase in division - should investigate whether ApoE affects cell cycle duration
Resulted in depletion of the overall pool of Type 1 NPCs over time - quantified with GFP expressing cells
Crews et al 2010
Increased BMP6 expression (Qrt-PCR) increased significantly in the brains of AD hippocampus in humans
Sections from the hippocampus of AD patients and nondemented controls were analyzed by immunohistochemistry with antibodies against the neuroblast marker DCX and the early NPC marker SOX2
Levels of SOX2 immunoreactivity were significantly reduced in the DG of AD hippocampus
Sim et al 2021
Phenotypic screening identified OXS-N1 as potent proneurogenic small molecule
Screening of 1080 compounds - selected from a chemical library of 25,000 compounds - has resulted in the identification of 30 active compounds belonging to 5 chemical classes
OXS-N1 increases neurogenesis in the dentate gyrus and improves cognition in wild type mice
Affinity probes synthesise to assess the molecular interactions of OXS-N1 - Identified to interact with vimentin - novel target.
Piccin et al 2014
In their work, NSCs were extracted from old brains and were transplanted into young brains
When placed into the younger environment, the older cells showed increased proliferation and migration, showing that behaviour is dictated by the environment (i.e elevated Wnt signalling)
Upon delivery of Wnt signalling molecules to the niche, (SB216763, a GSK-3b inhibitor, and Wnt3), NSC pools were expanded in vivo.
Sierra et al 2015
Disease environments
For instance, in a mouse model of epilepsy induced by kainic acid, demonstrated accelerated depletion of NSCs in response to neuronal hyper-excitation
Induced their activation and terminal differentiation to reactive astrocytes thereby exhausting the quiescent pool to supply the hippocampus
Kremer et al 2017
Unbiased proteomics screen to identify novel proteins expressed during neuronal differentiation using a human neural stem cell model,
Identified the proteoglycan Glypican-2 (Gpc2) as a putative secreted marker of immature neurons.
Exogenous Gpc2 binds to FGF2 and inhibits FGF2-induced neural progenitor cell proliferation. Gpc2 is enriched in neurogenic regions of the adult brain.
Gpc2 is detectable in adult human CSF, and first pilot experiments with a longitudinal cohort indicate a decrease over time.
Thus, Gpc2 may serve as a potential marker to monitor adult neurogenesis in both animal and human physiology and disease, warranting future studies.
BUT limited to only certain populations as SOX11 target gene - Long way to go
Kumagai et al 2009
Explored the impact of transplantation of neurogenic and gliogenic populations of NSCs (clarified by neurosphere assays), rodents
SCI induced in mice and cells injected into lesion epicentre after 9 days
Histological analyses were preformed after 6 weeks
Area of SC larger in gliogenic group - prevented atrophy
Immunohistochemistry - PECAM-1-positive blood vessels were observed at the lesion site
Beneficial role of stem cells is the paracrine effect they have on creating a suited environment to regrowth and repair - not physical contribution as a neuron.
Although the transplantation of primary neurospheres had no effect on the functional recovery from contusive SCI, it may be beneficial for neurological diseases in which particular types of early projection neurons are selectively lost - much shorter distances are required
Piccini et al 1999
D2 receptor occupancy measured with PET in PD patient to measure dopamine release from embryonic nigral transplants
In this patient, who had received a transplant in the right putamen 10 years earlier, grafts had restored both basal and drug-induced dopamine release to normal levels.
This was associated with sustained, marked clinical benefit and normalized levels of dopamine storage
However - inconsistent results with many patients experiencing dyskinesias
Yang et al 2017 (cell free)
Therapeutically, application of miRNAs involved in the neuroremodelling process (miR-124) via modified exosomes has been shown to protect against ischemic injury and promote cortical neural progenitors to obtain neuronal identity
A Phase I/II trial begun in October 2018, testing the outcomes of MSC-generated exosome with miR-124, one month after cerebral infarction. Nevertheless, rapid clearance by the innate immune system in vivo means retaining exosomes in the lesion site for an extended period of time is not realistic. Therefore use of nanotechnology, as above, could be employed to achieve sustained exosome release.
Preman et al 2021
Transplanting human induced pluripotent stem cell (hiPSC)-derived astrocyte progenitors expressing APOE ε3 (E3) or APOE ε4 (E4) into neonatal brains.
24 % of human astrocytes showing hypertrophic morphologies and thicker processes surrounding Aβ deposits, 12% showed atrophy
Proportion of human astrocytes undergoing morphological transformations lower in the chimeric AD brains than in the brains of AD patients
Perhaps poor modelling or allows us to study early stage of disease - not possible by tracking purely in-vivo
Failed to implicate importance of APOE genes with other elements of human pathophysiology - perhaps animal model does not facilitate such human specific disease mechanisms
Interesting to perform RNA sequencing analyses at single-cell resolution to dissect the cellular states of transplanted astrocyte -> not possible due to limited recovery after transplantation.
Livesey et al 2012
Human iPSCs manipulated to form stem cell cortical rosettes
Combining retinoid signaling with inhibition of SMAD signaling to promote neural induction -directed differentiation of hESCs to cerebral cortex stem cells with high efficiency - tested with rt-PCR (expression) and immunofluorescence images of rosettes
Synaptogenesis occurs in vitro - visualised with super-res microscopy tested functionality by observing patch-clamp - spontaneous firing
Activity independent synaptogenesis - we know in human. Epilepsy
Rowald et al 2022
Arrangement of electrodes targeting the ensemble of dorsal roots involved in leg and trunk movements
Developed a computational framework that informed the optimal arrangement of electrodes on a new paddle lead and guided its neurosurgical positioning personalized with MRI /CT
Developed software supporting the rapid configuration of activity-specific stimulation programs that reproduced the natural activation of motor neurons underlying each activity
Several successful case studies in patients regaining the ability to walk, swim, stand, cycle
However not natural movements any natural movement regained posited to be from remaining intact descending tracts that had become hypoactive through injury
Expensive as personalised therapy required
Improving the computational framework - Brain machine interfaces may improve activity-specific-stimulation programs.
Flugel et al 2001
EAE
MBP-specific T cells retrovirally engineered to express the gene of green fluorescent protein
Preceding disease onset, large numbers of effector cells invade the CNS, with only negligible numbers left in the periphery.
Reactivated upon local encounter of their cognate CNS antigen
