Combinatory strategies for promoting tissue remodelling and endogenous plasticity after experimental ischemic stroke

Ulike strategier for å fremme regenerering og endogen plastisitet i hjernen etter eksperimentelt iskemisk slag Hjerneslag er på verdensbasis en av sykdommene som rammer flest mennesker i tillegg til å ha høy dødelighet. Vi kan kategorisere hjerneslag i to hovedtyper; slag forårsaket av en blødning i hjernevevet, eller slag forårsaket av en blokkering av blodtilførselen i hjernen, også kalt iskemiske slag. De fleste pasienter som rammes av slag, rammes av iskemiske slag, enten ved trombose eller en embolisme som begge innebærer at plakk eller en blodpropp føres med blodstrømmen opp i hjernen og blir sittende fast der. Per i dag er det kun trombolyse, oppløsning av blokkeringen i arterien med tissue plasminogen activator (tPA), som er godkjent som klinisk behandling av slagpasienter. Dessverre er tPA kun effektivt i et kort tidsrom på ca. 3-4,5 timer etter blodtilførselen opphører, noe som fører til at mange pasienter ikke kan motta denne typen behandlingen grunnet forsinket ankomst til sykehuset. Med økende levealder og en økende eldre befolkning forventes det også at antallet nye slagtilfeller vil bli flere i årene som kommer. Sykdomsutviklingen og patologien til iskemiske slag er en sammensatt prosess som utvikler seg over tid, i tillegg til store forskjeller mellom pasienter, noe som gjør behandling svært utfordrende. En stor del av behandlingen dreier seg derfor i mange tilfeller om rehabilitering etter skaden har oppstått. Dette understreker hvorfor tilnærming til behandling bør fokusere på å kombinere ulike strategier, enten når det gjelder å bremse skadeutviklingen, eller reparere skaden som allerede har oppstått. Humane nevronale stamceller (hNSCs) har vist seg i dyremodeller å ha positiv effekt på mikromiljøet i skadeområdet og på inflammasjon. Det er også en mulighet for at hNSCs kan erstatte noe av det tapte vevet, men også stimulere hjernens eget potensiale for plastisitet og regenerasjon. I arbeidet som er presentert i denne avhandlingen beskrives det ulike tilnærminger til behandling av hjerneslag i eksperimentelle slagmodeller. Hovedmålet med arbeidet har vært a) å kombinere stamcelleterapi enten med andre celletyper eller med farmakologisk behandling for å se om dette øker effekten i forhold til stamcellebehandling alene; b) studere effekten av å modulere inflammatoriske prosesser på utvikling av skaden; c) ta i bruk histologiske metoder for å se på celleimplantatenes overlevelse og integrering i vevet; d) studere hjernens egen (endogene) kapasitet for regenerasjon og effekten av de ovennevnte behandlingene på denne responsen til skade; e) sammenligne to forskjellige dyremodeller og diskutere potensialet for klinisk translasjon ved bruk av disse i slagforskning. I avhandlingen presenteres og diskuteres resultatene av arbeidet, potensialet av å integrere forskjellige behandlinger, samt bruk av dyremodeller med tanke på klinisk translasjon

Neuroplasticity in stroke recovery. The role of microglia in engaging and modifying synapses and networks

Neuroplasticity after ischaemic injury involves both spontaneous rewiring of neural networks and circuits as well as functional responses in neurogenic niches. These events involve complex interactions with activated microglia, which evolve in a dynamic manner over time. Although the exact mechanisms underlying these interactions remain poorly understood, increasing experimental evidence suggests a determining role of pro‐ and anti‐inflammatory microglial activation profiles in shaping both synaptogenesis and neurogenesis. While the inflammatory response of microglia was thought to be detrimental, a more complex profile of the role of microglia in tissue remodelling is emerging. Experimental evidence suggests that microglia in response to injury can rapidly modify neuronal activity and modulate synaptic function, as well as be beneficial for the proliferation and integration of neural progenitor cells (NPCs) from endogenous neurogenic niches into functional networks thereby supporting stroke recovery. The manner in which microglia contribute towards sculpting neural synapses and networks, both in terms of activity‐dependent and homeostatic plasticity, suggests that microglia‐mediated pro‐ and/or anti‐inflammatory activity may significantly contribute towards spontaneous neuronal plasticity after ischaemic lesions. In this review, we first introduce some of the key cellular and molecular mechanisms underlying neuroplasticity in stroke and then proceed to discuss the crosstalk between microglia and endogenous neuroplasticity in response to brain ischaemia with special focus on the engagement of synapses and neural networks and their implications for grey matter integrity and function in stroke repair

Obesity-induced type 2 diabetes impairs neurological recovery after stroke in correlation with decreased neurogenesis and persistent atrophy of parvalbumin-positive interneurons

Type 2 diabetes (T2D) hampers stroke recovery though largely undetermined mechanisms. Few preclinical studies have investigated the effect of genetic/toxin-induced diabetes on long-term stroke recovery. However, the effects of obesity-induced T2D are mostly unknown. We aimed to investigate whether obesity-induced T2D worsens long-term stroke recovery through the impairment of brain's self-repair mechanisms - stroke-induced neurogenesis and parvalbumin (PV)+ interneurons-mediated neuroplasticity. To mimic obesity-induced T2D in the middle-age, C57bl/6j mice were fed 12 months with high-fat diet (HFD) and subjected to transient middle cerebral artery occlusion (tMCAO). We evaluated neurological recovery by upper-limb grip strength at 1 and 6 weeks after tMCAO. Gray and white matter damage, stroke-induced neurogenesis, and survival and potential atrophy of PV-interneurons were quantitated by immunohistochemistry (IHC) at 2 and 6 weeks after tMCAO. Obesity/T2D impaired neurological function without exacerbating brain damage. Moreover, obesity/T2D diminished stroke-induced neural stem cell (NSC) proliferation and neuroblast formation in striatum and hippocampus at 2 weeks after tMCAO and abolished stroke-induced neurogenesis in hippocampus at 6 weeks. Finally, stroke resulted in the atrophy of surviving PV-interneurons 2 weeks after stroke in both non-diabetic and obese/T2D mice. However, after 6 weeks, this effect selectively persisted in obese/T2D mice. We show in a preclinical setting of clinical relevance that obesity/T2D impairs neurological functions in the stroke recovery phase in correlation with reduced neurogenesis and persistent atrophy of PV-interneurons, suggesting impaired neuroplasticity. These findings shed light on the mechanisms behind impaired stroke recovery in T2D and could facilitate the development of new stroke rehabilitative strategies for obese/T2D patients

Effects of neural stem cell and olfactory ensheathing cell co-transplants on tissue remodelling after transient focal cerebral ischemia in the adult rat

Effective transplant-mediated repair of ischemic brain lesions entails extensive tissue remodeling, especially in the ischemic core. Neural stem cells (NSCs) are promising reparative candidates for stroke induced lesions, however, their survival and integration with the host-tissue post-transplantation is poor. In this study, we address this challenge by testing whether co-grafting of NSCs with olfactory ensheathing cells (OECs), a special type of glia with proven neuroprotective, immunomodulatory, and angiogenic effects, can promote graft survival and host tissue remodelling. Transient focal cerebral ischemia was induced in adult rats by a 60-min middle cerebral artery occlusion (MCAo) followed by reperfusion. Ischemic lesions were verified by neurological testing and magnetic resonance imaging. Transplantation into the globus pallidus of NSCs alone or in combination with OECs was performed at two weeks post-MCAo, followed by histological analyses at three weeks post-transplantation. We found evidence of extensive vascular remodelling in the ischemic core as well as evidence of NSC motility away from the graft and into the infarct border in severely lesioned animals co-grafted with OECs. These findings support a possible role of OECs as part of an in situ tissue engineering paradigm for transplant mediated repair of ischemic brain lesions

L-DOPA-Coated Manganese Oxide Nanoparticles as Dual MRI Contrast Agents and Drug-Delivery Vehicles

Manganese oxide nanoparticles (MONPs) are capable of time‐dependent magnetic resonance imaging contrast switching as well as releasing a surface‐bound drug. MONPs give T2/T2* contrast, but dissolve and release T1‐active Mn2+ and L‐3,4‐dihydroxyphenylalanine. Complementary images are acquired with a single contrast agent, and applications toward Parkinson's disease are suggested

Normalisation of glucose metabolism by exendin-4 in the chronic phase after stroke promotes functional recovery in male diabetic mice

Background and Purpose: Glucagon-like peptide-1 (GLP-1) receptor activation decreases stroke risk in people with Type 2 diabetes (T2D), while animal studies have shown the efficacy of this strategy to counteract stroke-induced acute brain damage. However, whether GLP-1 receptor activation also improves recovery in the chronic phase after stroke is unknown. We investigated whether post-acute, chronic administration of the GLP-1 receptor agonist, exendin-4, improves post-stroke recovery and examined possible underlying mechanisms in T2D and non-T2D mice. Experimental Approach: We induced stroke via transient middle cerebral artery occlusion (tMCAO) in T2D/obese mice (8 months of high-fat diet) and age-matched controls. Exendin-4 was administered for 8 weeks from Day 3 post-tMCAO. We assessed functional recovery by weekly upper-limb grip strength tests. Insulin sensitivity and glycaemia were evaluated at 4 and 8 weeks post-tMCAO. Neuronal survival, stroke-induced neurogenesis, neuroinflammation, atrophy of GABAergic parvalbumin+ interneurons, post-stroke vascular remodelling and fibrotic scar formation were investigated by immunohistochemistry. Key Results: Exendin-4 normalised T2D-induced impairment of forepaw grip strength recovery in correlation with normalised glycaemia and insulin sensitivity. Moreover, exendin-4 counteracted T2D-induced atrophy of parvalbumin+ interneurons and decreased microglia activation. Finally, exendin-4 normalised density and pericyte coverage of micro-vessels and restored fibrotic scar formation in T2D mice. In non-T2D mice, the exendin-4-mediated recovery was minor. Conclusion and Implications: Chronic GLP-1 receptor activation mediates post-stroke functional recovery in T2D mice by normalising glucose metabolism and improving neuroplasticity and vascular remodelling in the recovery phase. The results warrant clinical trial of GLP-1 receptor agonists for rehabilitation after stroke in T2D