MR elastography detection of early viscoelastic response of the murine hippocampus to amyloid ß accumulation and neuronal cell loss due to Alzheimer's disease.

PURPOSE: To investigate in vivo viscoelastic parameters related to early histopathological changes in the hippocampus and the cortex in early, preclinical Alzheimer's disease (AD) stages. MATERIALS AND METHODS: Magnetic resonance elastography (MRE) was applied to female APP23 mice, an established transgenic mouse model of AD, at three different stages early in disease progression. To investigate the potential therapeutic effects of physical, cognitive, and social stimulation on brain viscoelasticity and histopathological characteristics, MRE was also applied after exposing young APP23 mice to environmentally enriched cage conditions (ENR), for 1, 12, or 24 weeks, which corresponds to adolescent, young-adult, and adult age at the time of analysis. RESULTS: Viscosity in the hippocampus of APP23 mice is lower than in controls (CTR) (P = 0.005) and does not increase with age, as in CTR mice (adolescent vs. young-adult: P = 1.000, vs. adult: P = 0.493, young-adult vs. adult: P = 1.000). Hippocampal cell numbers decrease with disease progression in APP23 mice (P < 0.001). Elasticity in the hippocampus is also reduced in APP23 mice (P = 0.024) but increases (P = 0.027) with disease progression. ENR in APP23 mice transiently increased hippocampal cell numbers (P = 0.002) but not viscosity (P = 0.838). CONCLUSION: MRE detects alterations in viscoelasticity in the hippocampus related to early histopathological changes in the APP23 mouse model of AD. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:105-114.

Physical activity compensates for isoflurane-induced selective impairment of neuronal progenitor cell proliferation in the young adult hippocampus.

General anesthesia is considered a risk factor for postoperative cognitive dysfunction. However, it is unclear what the neuronal and cognitive consequences of general anesthesia are and whether they can be treated. One possible pathomechanism is hippocampal neurogenesis. We investigated how the anesthetic isoflurane affects adult hippocampal neurogenesis and associated cognitive functions and whether the neurogenic stimulus of physical activity reverses isoflurane-induced changes. We exposed young adult mice to isoflurane (ISO) - half had access to a running wheel (ISO-RW). Both groups were compared with a control condition (CTR; CTR-RW). Cell proliferation and survival in the dentate gyrus of the hippocampus were quantified histologically 48 h and 3 weeks after anesthesia by bromodeoxyuridine incorporation. Cell phenotype was determined by expression of neuronal markers, and the extent of continuous endogenous neuronal proliferation was estimated from the number of doublecortin-positive cells. The Morris water maze was used to test hippocampus-dependent functions. We found that isoflurane decreased proliferation of neuronal progenitor cells, whereas survival of mature neurons remained intact. Consistent with intact neuronal survival, spatial memory associated with neurogenesis also proved intact in the Morris water maze despite isoflurane exposure. Physical activity attenuated the observed neuronal changes by preventing the decrease in newborn neuronal progenitor cells and the decline in continuous endogenous neuronal proliferation in isoflurane-treated animals. In conclusion, isoflurane selectively impairs neuronal proliferation but not survival or neurogenesis-linked cognition in adult mice. The observed adverse effects can be attenuated by physical activity, a cost-effective means of preventing the neurogenic consequences of general anesthesia.

Sleeping Beauty transposon system for GDNF overexpression of entrapped stem cells in fibrin hydrogel in a rat model of Parkinson's disease.

There is currently no causal treatment available for Parkinson's disease (PD). However, the use of glial cell line-derived neurotrophic factor (GDNF) to provide regenerative effects for neurons is promising. Such approaches require translational delivery systems that are functional in diseased tissue. To do so, we used a non-viral Sleeping Beauty (SB) transposon system to overexpress GDNF in adipose tissue-derived mesenchymal stromal cells (adMSCs). Entrapment of cells in fibrin hydrogel was used to boost potential neurorestorative effects. Functional GDNF-adMSCs were able to secrete 1066.8 ± 169.4 ng GDNF/120,000 cells in vitro. The GDNF-adMSCs were detectable for up to 1 month after transplantation in a mild 6-hydroxydopamine (6-OHDA) hemiparkinson male rat model. Entrapment of GDNF-adMSCs enabled GDNF secretion in surrounding tissue in a more concentrated manner, also tending to prolong GDNF secretion relatively. GDNF-adMSCs entrapped in hydrogel also led to positive immunomodulatory effects via an 83% reduction of regional IL-1ß levels compared to the non-entrapped GDNF-adMSC group after 1 month. Furthermore, GDNF-adMSC-treated groups showed higher recovery of tyrosine hydroxylase (TH)-expressing cells, indicating a neuroprotective function, although this was not strong enough to show significant improvement in motor performance. Our findings establish a promising GDNF treatment system in a PD model. Entrapment of GDNF-adMSCs mediated positive immunomodulatory effects. Although the durability of the hydrogel needs to be extended to unlock its full potential for motor improvements, the neuroprotective effects of GDNF were evident and safe. Further motor behavioral tests and other disease models are necessary to evaluate this treatment option adequately.

Transposon-mediated glial cell line-derived neurotrophic factor overexpression in human adipose tissue-derived mesenchymal stromal cells: A potential approach for neuroregenerative medicine?

Glial cell line-derived neurotrophic factor (GDNF) has neuroprotective effects and may be a promising candidate for regenerative strategies focusing on neurodegenerative diseases. As GDNF cannot cross the blood-brain barrier to potentially regenerate damaged brain areas, continuous in situ delivery with host cells is desired. Here, a non-viral Sleeping Beauty transposon was used to achieve continuous in vitro overexpression of GDNF in immune-privileged human adipose tissue-derived mesenchymal stromal cells (GDNF-tASCs). In addition, in vivo survival, tolerance, and effectiveness of transfected cells were tested in a very mild 6-hydroxydopamine (6-OHDA)-induced dopamine depletion rat model by means of intrastriatal injection on a sample basis up to 6 months after treatment. GDNF-tASCs showed vast in vitro gene overexpression up to 13 weeks post-transfection. In vivo, GDNF was detectable 4 days following transplantation, but no longer after 1 month, although adipose tissue-derived mesenchymal stromal cells (ASCs) could be visualized histologically even after 6 months. Despite successful long-term in vitro GDNF overexpression and its in vivo detection shortly after cell transplantation, the 6-OHDA model was too mild to enable sufficient evaluation of in vivo disease improvement. Still, in vivo immunocompatibility could be further examined. ASCs initially induced a pronounced microglial accumulation at transplantation site, particularly prominent in GDNF-tASCs. However, 6-OHDA-induced pro-inflammatory immune response was attenuated by ASCs, although delayed in the GDNF-tASCs group. To further test the therapeutic potential of the generated GDNF-overexpressing cells in a disease-related context, a follow-up study using a more appropriate 6-OHDA model is needed.

Dietary-challenged mice with Alzheimer-like pathology show increased energy expenditure and reduced adipocyte hypertrophy and steatosis.

Alzheimer's disease (AD) is frequently accompanied by progressing weight loss, correlating with mortality. Counter-intuitively, weight loss in old age might predict AD onset but obesity in midlife increases AD risk. Furthermore, AD is associated with diabetes-like alterations in glucose metabolism. Here, we investigated metabolic features of amyloid precursor protein overexpressing APP23 female mice modeling AD upon long-term challenge with high-sucrose (HSD) or high-fat diet (HFD). Compared to wild type littermates (WT), APP23 females were less prone to mild HSD-induced and considerable HFD-induced glucose tolerance deterioration, despite unaltered glucose tolerance during normal-control diet. Indirect calorimetry revealed increased energy expenditure and hyperactivity in APP23 females. Dietary interventions, especially HFD, had weaker effects on lean and fat mass gain, steatosis and adipocyte hypertrophy of APP23 than WT mice, as shown by 1H-magnetic-resonance-spectroscopy, histological and biochemical analyses. Proteome analysis revealed differentially regulated expression of mitochondrial proteins in APP23 livers and brains. In conclusion, hyperactivity, increased metabolic rate, and global mitochondrial dysfunction potentially add up to the development of AD-related body weight changes in APP23 females, becoming especially evident during diet-induced metabolic challenge. These findings emphasize the importance of translating this metabolic phenotyping into human research to decode the metabolic component in AD pathogenesis.

Biomechanical properties of the hypoxic and dying brain quantified by magnetic resonance elastography.

Respiratory arrest is a major life-threatening condition leading to cessation of vital functions and hypoxic-anoxic injury of the brain. The progressive structural tissue changes characterizing the dying brain biophysically are unknown. Here we use noninvasive magnetic resonance elastography to show that biomechanical tissue properties are highly sensitive to alterations in the brain in the critical period before death. Our findings demonstrate that brain stiffness increases after respiratory arrest even when cardiac function is still preserved. Within 5 min of cardiac arrest, cerebral stiffness further increases by up to 30%. This early mechanical signature of the dying brain can be explained by water accumulation and redistribution from extracellular spaces into cells. These processes, together, increase interstitial and intracellular pressure as revealed by magnetic resonance spectroscopy and diffusion-weighted imaging. Our data suggest that the fast response of cerebral stiffness to respiratory arrest enables the monitoring of life-threatening brain pathology using noninvasive in vivo imaging. STATEMENT OF SIGNIFICANCE: Hypoxia-anoxia is a life-threatening condition eventually leading to brain death. Therefore, monitoring vital brain functions in patients at risk is urgently required during emergency care or treatment of acute brain damage due to insufficient oxygen supply. In mouse model of hypoxia-anoxia, we have shown for the first time that biophysical tissue parameters such as brain stiffness changed markedly during the process of death.

Chia seeds as a potential cognitive booster in the APP23 Alzheimer's disease model.

Glucose hypometabolism potentially contributes to Alzheimer's disease (AD) and might even represent an underlying mechanism. Here, we investigate the relationship of diet-induced metabolic stress and AD as well as the therapeutic potential of chia seeds as a modulator of glucose metabolism in the APP23 mouse model. 4-6 (pre-plaque stage, PRE) and 28-32 (advanced-plaque stage, ADV) weeks old APP23 and wild type mice received pretreatment for 12 weeks with either sucrose-rich (SRD) or control diet, followed by 8 weeks of chia seed supplementation. Although ADV APP23 mice generally showed functioning glucose homeostasis, they were more prone to SRD-induced glucose intolerance. This was accompanied by elevated corticosterone levels and mild insulin insensitivity. Chia seeds improved spatial learning deficits but not impaired cognitive flexibility, potentially mediated by amelioration of glucose tolerance, attenuation of corticosterone levels and reversal of SRD-induced elevation of pro-inflammatory cytokine levels. Since cognitive symptoms and plaque load were not aggravated by SRD-induced metabolic stress, despite enhanced neuroinflammation in the PRE group, we conclude that impairments of glucose metabolism do not represent an underlying mechanism of AD in this mouse model. Nevertheless, chia seeds might provide therapeutic potential in AD as shown by the amelioration of cognitive symptoms.

The influence of body temperature on tissue stiffness, blood perfusion, and water diffusion in the mouse brain.

While hypothermia of the brain is used to reduce neuronal damage in patients with conditions such as traumatic brain injury or stroke, little is known about how temperature affects the biophysical properties of in vivo brain tissue. Therefore, we measured shear wave speed (SWS), apparent diffusion coefficient (ADC), and cerebral blood flow (CBF) in the mouse brain at different body temperatures to investigate the relationship between temperature and tissue stiffness, water diffusion, and blood perfusion in the living brain. Multifrequency magnetic resonance elastography (MRE), diffusion-weighted imaging (DWI), and arterial spin labeling (ASL) were performed in seven mice while increasing and recording body temperature from hypothermia (28-30 °C) to normothermia (36-38 °C). SWS, ADC, and CBF were analyzed in regions of whole brain, cortex, hippocampus, and diencephalon. Our results show that SWS decreases while ADC and CBF increase from hypothermia to normothermia (whole brain SWS: -6.2%, ADC: +34.0%, CBF: +80.2%; cortex SWS: -10.1%, ADC: +30.9%, CBF: +82.4%; all p > 0.05). We found a significant inverse correlation between SWS and both ADC and CBF in all analyzed regions except diencephalon (whole brain SWS-ADC: r = -0.8, p < 0.005; SWS-CBF: r = -0.84, p < 0.005; cortex SWS-ADC: r = -0.74, p < 0.05; SWS-CBF: r = -0.65, p < 0.05). These results show that in vivo brain stiffness is inversely correlated with temperature, extracellular water mobility, and microvascular blood flow. Regional differences indicate that cortical areas are more markedly affected by hypothermia than central regions such as diencephalon. Temperature should be considered as a confounder in elastographic measurements, especially in preclinical settings. STATEMENT OF SIGNIFICANCE: Hibernating mammals lower their body temperature and metabolic activity. A hypothermic state can also be induced for medical purposes to reduce the risk of neural damage in patients with neurological disease or injury. However, little is known how physical soft-tissue properties of the in-vivo brain such as water diffusion, blood perfusion or mechanical parameters correlate with each other when temperature changes. Our study demonstrates for the first time that those quantitative imaging markers are tightly linked to changes in body temperature. While water diffusion and blood perfusion are reduced during hypothermia, brain stiffness significantly increases, suggesting that multiparametric quantitative MRI should be used for the noninvasive assessment of brain metabolic activity.

Brain maturation is associated with increasing tissue stiffness and decreasing tissue fluidity.

Biomechanical cues guide proliferation, growth and maturation of neurons. Yet the molecules that shape the brain's biomechanical properties are unidentified and the relationship between neural development and viscoelasticity of brain tissue remains elusive. Here we combined novel in-vivo tomoelastography and ex-vivo proteomics to investigate whether viscoelasticity of the mouse brain correlates with protein alterations within the critical phase of brain maturation. For the first time, high-resolution atlases of viscoelasticity of the mouse brain were generated, revealing that (i) brain stiffness increased alongside progressive accumulation of microtubular structures, myelination, cytoskeleton linkage and cell-matrix attachment, and that (ii) viscosity-related tissue fluidity decreased alongside downregulated actin crosslinking and axonal organization. Taken together, our results show that brain maturation is associated with a shift of brain mechanical properties towards a more solid-rigid behavior consistent with reduced tissue fluidity. This shift appears to be driven by several molecular processes associated with myelination, cytoskeletal crosslinking and axonal organization. STATEMENT OF SIGNIFICANCE: The viscoelastic properties of brain tissue shape the environment in which neurons proliferate, grow, and mature. In the present study, novel tomoelastography was used to spatially map tissue mechanical properties of the in-vivo mouse brain during maturation. In vivo tomoelastography was also combined with ex vivo mass spectrometry proteomic analysis to identify the molecules which shape the biomechanical properties of brain tissue. With the combined technique, we observed that brain maturation is associated with a shift of brain mechanical properties towards a more solid-rigid behavior consistent with reduced tissue fluidity which is driven by multiple molecular processes. We believe that this shift of brain mechanical properties discovered in our study reflects a fundamental biophysical signature of brain maturation.

Behavioral and psychological symptoms of dementia (BPSD) and impaired cognition reflect unsuccessful neuronal compensation in the pre-plaque stage and serve as early markers for Alzheimer's disease in the APP23 mouse model.

Recent research on Alzheimer's disease (AD) focuses on processes prior to amyloid-beta plaque deposition accounting for the progress of the disease. However, early mechanisms of AD are still poorly understood and predictors of the disease in the pre-plaque stage essential for initiating an early therapy are lacking. Behavioral and psychological symptoms of dementia (BPSD) and potentially impaired cognition may serve as predictors and early clinical diagnostic markers for AD. To investigate potential BPSD and cognitive impairments in association with neuronal cell development as such markers for AD in the pre-plaque stage, female APP23 mice at eight, 19 and 31 weeks of age and corresponding control animals were tested for BPSD (elevated zero maze; sucrose preference test), motor coordination (rotarod), spatial memory and reversal learning (Morris water maze) and hippocampal neurogenesis as a neuronal correlate for hippocampus-dependent behavior. To evaluate a potential therapeutic effect of physical, cognitive and social stimulation, animals were exposed to environmental enrichment (EE) for one, twelve or 24 weeks from five weeks of age. In APP23, decreased anxiety accompanied increased agitation from eight weeks of age. Impairment of spatial memory and learning flexibility prior to plaque deposition involved an insufficient use of spatial search strategies associated with an unsuccessful compensatory increase of neurogenesis. EE had an overall beneficial effect on behavior and neurogenesis and thus constitutes a therapeutic tool to slow disease progression. BPSD, cognition and associated impaired neurogenesis complement clinical diagnostic markers for pre-plaque AD and contribute to an early detection essential to halt disease progression.

Memory enhancement by ferulic acid ester across species.

Cognitive impairments can be devastating for quality of life, and thus, preventing or counteracting them is of great value. To this end, the present study exploits the potential of the plant Rhodiola rosea and identifies the constituent ferulic acid eicosyl ester [icosyl-(2E)-3-(4-hydroxy-3-methoxyphenyl)-prop-2-enoate (FAE-20)] as a memory enhancer. We show that food supplementation with dried root material from R. rosea dose-dependently improves odor-taste reward associative memory scores in larval Drosophila and prevents the age-related decline of this appetitive memory in adult flies. Task-relevant sensorimotor faculties remain unaltered. From a parallel approach, a list of candidate compounds has been derived, including R. rosea-derived FAE-20. Here, we show that both R. rosea-derived FAE-20 and synthetic FAE-20 are effective as memory enhancers in larval Drosophila. Synthetic FAE-20 also partially compensates for age-related memory decline in adult flies, as well as genetically induced early-onset loss of memory function in young flies. Furthermore, it increases excitability in mouse hippocampal CA1 neurons, leads to more stable context-shock aversive associative memory in young adult (3-month-old) mice, and increases memory scores in old (>2-year-old) mice. Given these effects, and given the utility of R. rosea-the plant from which we discovered FAE-20-as a memory enhancer, these results may hold potential for clinical applications.