Candidate molecular pathways of white matter vulnerability in the brain of normal aging rhesus monkeys

Inhibitory effect of lanosterol on cataractous lens of cynomolgus monkeys using a subconjunctival drug release system

Background

To evaluate the effect of lanosterol on cataractous lens of cynomolgus monkeys using a subconjunctival drug release system.

Methods

Nine elder cynomolgus monkeys were used, consisting of three monkeys without cataract as controls, three monkeys with naturally occurring cortical cataract, and three monkeys with nuclear cataract as intervention groups. Nanoparticulated thermogel with lanosterol and fluorescein was administered by subconjunctival injection in the monkeys with cataract. Fluorescence changes of injected thermogel and cataract progression were observed. Lanosterol concentration in aqueous humor, solubility changes in lens proteins, and oxidative stress levels were analyzed in the lenses of the control and intervention groups.

Results

Injected thermogel showed decreased fluorescence during follow up. Lanosterol concentration in aqueous humor increased in the first 2 weeks and then gradually decreased, which was in accordance with the changes in cortical lens clarity. However, lenses with nuclear opacification showed little change. In the cortical region of lenses with cortical cataract, solubility of α-crystallin was significantly increased after administration of lanosterol, as well as the reduction of oxidative stress.

Conclusions

We demonstrated the effect of lanosterol on cataract progression based on in vivo models of primates. Lanosterol showed a short-term and reliable reversal effect on reducing cataract severity in cortical cataract in the early stages, possibly due to the increase in the solubility of lens proteins and changes in the oxidative stress status. Lanosterol administration using subconjunctival drug release system could be a promising nonsurgical approach for future clinical studies of cataract prevention and treatment.

rTMS alleviates AD-induced cognitive impairment by inhibitng apoptosis in SAMP8 mouse

This study sought to investigate whether repetitive transcranial magnetic stimulation (rTMS) could alleviate cognitive dysfunction in SAMP8 mice by reducing cell apoptosis and activating the cAMP/PKA/CREB signalling pathway. A total of 40 SAMP8 mice were randomly assigned to the SAMP8 group (n=20), and rTMS treatment group (rTMS+SAMP8, n=20); additionally, 20 homologous and normal aged SAMR1 mice were used as the control group(n=20). The Morris water maze and Y maze tests were applied to evaluate spatial learning and memory ability. Haematoxylin and eosin (HE) staining and terminal-deoxynucleotidyl transferase-mediated nick end labelling (TUNEL) were used to observe the changes in neurons in the cortex and hippocampus. Western blotting and RT-PCR were used to detect signalling related proteins. rTMS significantly improved spatial learning and memory deficits and morphological abnormalities in the hippocampus region of the hippocampus. In addition, rTMS reduced apoptosis of neurons caused by AD and the expression of pro-apoptotic proteins (Caspase-3 and Bax) and increased the expression of an antiapoptotic protein (Bcl-2). Furthermore, rTMS activated the cAMP/PKA/CREB signalling pathway. These results showed that rTMS could ameliorate cognitive deficits in AD mice by inhibiting apoptosis via activation the cAMP/PKA/CREB signalling pathway.

Sleep deprivation impairs cognitive performance, alters task-associated cerebral blood flow and decreases cortical neurovascular coupling-related hemodynamic responses

Sleep deprivation (SD) is a common condition and an important health concern. In addition to metabolic and cardiovascular risks, SD associates with decreases in cognitive performance. Neurovascular coupling (NVC, "functional hyperemia") is a critical homeostatic mechanism, which maintains adequate blood supply to the brain during periods of intensive neuronal activity. To determine whether SD alters NVC responses and cognitive performance, cognitive and hemodynamic NVC assessments were conducted prior to and 24 h post-SD in healthy young male individuals (n = 10, 27 ± 3 years old). Cognition was evaluated with a battery of tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB). Hemodynamic components of NVC were measured by transcranial Doppler sonography (TCD) during cognitive stimulation, dynamic retinal vessel analysis (DVA) during flicker light stimulation, and functional near infrared spectroscopy (fNIRS) during finger tapping motor task. Cognitive assessments revealed impairments in reaction time and sustained attention after 24 h of SD. Functional NIRS analysis revealed that SD significantly altered hemodynamic responses in the prefrontal cortex and somatosensory cortex during a motor task. NVC-related vascular responses measured by DVA and TCD did not change significantly. Interestingly, TCD detected decreased task-associated cerebral blood flow (CBF) in the right middle cerebral artery in sleep deprived participants. Our results demonstrate that 24 h of SD lead to impairments in cognitive performance together with altered CBF and hemodynamic components of cortical NVC responses.

Differential associations of engagement in physical activity and estimated cardiorespiratory fitness with brain volume in middle-aged to older adults

Previous work has confirmed the benefits of aerobic exercise for brain aging, however mechanisms underlying these effects remain unclear. Two measures of exercise, time spent in moderate-to-vigorous physical activity (MVPA) and cardiorespiratory fitness (CRF), may reflect different pathways linking activity to brain health. Using data from the UK Biobank, the largest sample combining neuroimaging and objectively measured MVPA available to date (n = 7148, n_male = 3062, n_female = 4086; age = 62.14 ± 7.40 years), we found that, when adjusted for covariates including MVPA, CRF was positively associated with overall gray matter volume (FDR p = 1.28E-05). In contrast, when adjusted for covariates including CRF, MVPA was positively associated with left and right hippocampal (FDR p_left = 0.01; FDR p_right = 0.02) volumes, but not overall gray matter volume. Both CRF and MVPA were inversely associated with white matter hyperintensity lesion loads (FDR p_CRF = 0.002; p_MVPA = 0.02). Our results suggest separable effects of engagement in exercise behaviors (MVPA) and the physiological effects of exercise (CRF) on structural brain volumes, which may have implications for differential pathways linking exercise and brain benefits.

How repetitive traumatic injury alters long-term brain function

BACKGROUND

How recurrent traumatic brain injury (rTBI) alters brain function years after insult is largely unknown. This study aims to characterize the mechanistic cause for long-term brain deterioration following rTBI using a rat model.

METHODS

Eighteen Sprague-Dawley wild-type rats underwent bilateral rTBI using a direct skull impact device or sham treatment, once per week for 5 weeks, and were euthanized 56 weeks after the first injury. Weekly rotarod performance measured motor deficits. Beam walk and grip strength were also assessed. Brain tissue were stained and volume was computed using Stereo Investigator's Cavalieri Estimator. The L5 cortical layer proximal to the injury site was microdissected and submitted for sequencing with count analyzed using R "DESeq2" and "GOStats." Brain-derived neurotrophic factor (BDNF) levels were determined using enzyme-linked immunosorbent assay.

RESULTS

Rotarod data demonstrated permanent deficits 1 year after rTBI. Decreased beam walk performance and grip strength was noted among rTBI rodents. Recurrent traumatic brain injury led to thinner cortex and thinner corpus callosum, enlarged ventricles, and differential expression of 72 genes (25 upregulated, 47 downregulated) including dysregulation of those associated with TBI (BDNF, NR4A1/2/3, Arc, and Egr) and downregulation in pathways associated with neuroprotection and neuroplasticity. Over the course of the study, BDNF levels decreased in both rTBI and sham rodents, and at each time point, the decrease in BDNF was more pronounced after rTBI.

CONCLUSION

Recurrent traumatic brain injury causes significant long-term alteration in brain health leading to permanent motor deficits, cortical and corpus callosum thinning, and expansion of the lateral ventricles. Gene expression and BDNF analysis suggest a significant drop in pathways associated with neuroplasticity and neuroprotection. Although rTBI may not cause immediate neurological abnormalities, continued brain deterioration occurs after the initial trauma in part due to a decline in genes associated with neuroplasticity and neuroprotection.

Proceedings from the Albert Charitable Trust Inaugural Workshop on white matter and cognition in aging

This third in a series of vascular cognitive impairment (VCI) workshops, supported by "The Leo and Anne Albert Charitable Trust," was held from February 8 to 12 at the Omni Resort in Carlsbad, CA. This workshop followed the information gathered from the earlier two workshops suggesting that we focus more specifically on brain white matter in age-related cognitive impairment. The Scientific Program Committee (Frank Barone, Shawn Whitehead, Eric Smith, and Rod Corriveau) assembled translational, clinical, and basic scientists with unique expertise in acute and chronic white matter injury at the intersection of cerebrovascular and neurodegenerative etiologies. As in previous Albert Trust workshops, invited participants addressed key topics related to mechanisms of white matter injury, biomarkers of white matter injury, and interventions to prevent white matter injury and age-related cognitive decline. This report provides a synopsis of the presentations and discussions by the participants, including the existing knowledge gaps and the delineation of the next steps towards advancing our understanding of white matter injury and age-related cognitive decline. Workshop discussions and consensus resulted in action by The Albert Trust to (1) increase support from biannual to annual "White Matter and Cognition" workshops; (2) provide funding for two collaborative, novel research grants annually submitted by meeting participants; and (3) coordinate the formation of the "Albert Research Institute for White Matter and Cognition." This institute will fill a gap in white matter science, providing white matter and cognition communications, including annual updates from workshops and the literature and interconnecting with other Albert Trust scientific endeavors in cognition and dementia, and providing support for newly established collaborations between seasoned investigators and to the development of talented young investigators in the VCI-dementia (VCID) and white matter cognition arena.

Inflammaging phenotype in rhesus macaques is associated with a decline in epithelial barrier-protective functions and increased pro-inflammatory function in CD161-expressing cells

The development of chronic inflammation, called inflammaging, contributes to the pathogenesis of age-related diseases. Although it is known that both B and T lymphocyte compartments of the adaptive immune system deteriorate with advancing age, the impact of aging on immune functions of Th17-type CD161-expressing innate immune cells and their role in inflammaging remain incompletely understood. Here, utilizing the nonhuman primate model of rhesus macaques, we report that a dysregulated Th17-type effector function of CD161+ immune cells is associated with leaky gut and inflammatory phenotype of aging. Higher plasma levels of inflammatory cytokines IL-6, TNF-α, IL-1β, GM-CSF, IL-12, and Eotaxin correlated with elevated markers of gut permeability including LPS-binding protein (LBP), intestinal fatty acid binding protein (I-FABP), and sCD14 in aging macaques. Further, older macaques displayed significantly lower frequencies of circulating Th17-type immune cells comprised of CD161+ T cell subsets, NK cells, and innate lymphoid cells. Corresponding with the increased markers of gut permeability, production of the type-17 cytokines IL-17 and IL-22 was impaired in CD161+ T cell subsets and NK cells, along with a skewing towards IFN-γ cytokine production. These findings suggest that reduced frequencies of CD161+ immune cells along with a specific loss in Th17-type effector functions contribute to impaired gut barrier integrity and systemic inflammation in aging macaques. Modulating type-17 immune cell functions via cytokine therapy or dietary interventions towards reducing chronic inflammation in inflammaging individuals may have the potential to prevent or delay age-related chronic diseases and improve immune responses in the elderly population.

Lipopolysaccharide exposure in a rat sepsis model results in hippocampal amyloid-β plaque and phosphorylated tau deposition and corresponding behavioral deficits

Sepsis is a severe systemic inflammatory response to infection associated with acute and chronic neurocognitive consequences, including an increased risk of later-life dementia. In a lipopolysaccharide-induced rat sepsis model, we have demonstrated neuroinflammation, cortical amyloid-beta plaque deposition, and increased whole brain levels of phosphorylated tau. Hippocampal abnormalities, particularly those of the dentate gyrus, are seen in Alzheimer's disease and age-related memory loss. The focus of this study was to determine whether Aβ plaques and phosphorylated tau aggregates occur in the hippocampus as a consequence of lipopolysaccharide administration, and whether behavioral abnormalities related to the hippocampus, particularly the dentate gyrus, can be demonstrated. Male Sprague Dawley rats received an intraperitoneal injection of 10 mg/kg of lipopolysaccharide endotoxin. Control animals received a saline injection. Seven days post injection, Aβ plaques and phosphorylated tau in the hippocampus were quantified following immunostaining. Behavioral tests that have previously been shown to result in specific deficits in dentate gyrus-lesioned rats were administered. Lipopolysaccharide treatment results in the deposition of beta amyloid plaques and intracellular phosphorylated tau in the hippocampus, including the dorsal dentate gyrus. Lipopolysaccharide treatment resulted in behavioral deficits attributable to the dorsal dentate gyrus, including episodic-like memory function that primarily involves spatial, contextual, and temporal orientation and integration. Lipopolysaccharide administration results in hippocampal deposition of amyloid-beta plaques and intracellular phosphorylated tau and results in specific behavioral deficits attributable to the dorsal dentate gyrus. These findings, if persistent, could provide a basis for the higher rate of dementia in longitudinal studies of sepsis survivors.

Dysregulation of the SNARE-binding protein Munc18-1 impairs BDNF secretion and synaptic neurotransmission: a novel interventional target to protect the aging brain

Brain-derived neurotrophic factor (BDNF) has a central role in maintaining and strengthening neuronal connections and to stimulate neurogenesis in the adult brain. Decreased levels of BDNF in the aging brain are thought to usher cognitive impairment. BDNF is stored in dense core vesicles and released through exocytosis from the neurites. The exact mechanism for the regulation of BDNF secretion is not well understood. Munc18-1 (STXBP1) was found to be essential for the exocytosis of synaptic vesicles, but its involvement in BDNF secretion is not known. Interestingly, neurons lacking munc18-1 undergo severe degeneration in knock-out mice. Here, we report the effects of BDNF treatment on the presynaptic terminal using munc18-1-deficient neurons. Reduced expression of munc18-1 in heterozygous (+/-) neurons diminishes synaptic transmitter release, as tested here on individual synaptic connections with FM1-43 fluorescence imaging. Transduction of cultured neurons with BDNF markedly increased BDNF secretion in wild-type but was less effective in munc18-1 +/- cells. In turn, BDNF enhanced synaptic functions and restored the severe synaptic dysfunction induced by munc18-1 deficiency. The role of munc18-1 in the synaptic effect of BDNF is highlighted by the finding that BDNF upregulated the expression of munc18-1 in neurons, consistent with enhanced synaptic functions. Accordingly, this is the first evidence showing the functional effect of BDNF in munc18-1 deficient synapses and about the direct role of munc18-1 in the regulation of BDNF secretion. We propose a molecular model of BDNF secretion and discuss its potential as therapeutic target to prevent cognitive decline in the elderly.