Neuronal Stress Resistance Research Articles

12‐weeks of caloric restriction diet improves cortical cerebral blood flow in healthy middle‐age adults

AbstractBackgroundCaloric restriction (CR) improves neuronal stress resistance in animals and improves cognitive performance in older adults (1‐3). Neuroinflammation is an increasingly recognized mechanism relevant to Alzheimer disease (AD). We investigated the effect of a 12‐week CR diet on imaging markers of dementia and neuroinflammation in midlife individuals with multiple sclerosis (MS), a prototype neuroinflammatory disease.MethodsIn a single‐blind randomized controlled trial, 10 participants with MS (8 women and 2 men, age: 45.5±10.67 and education: 16.4±2.5 years) were recruited from the Washington University John L. Trotter MS Center and randomly assigned to participate in either a 12‐week CR or control group on their regular diet. Participants fasted 2 days a week and during those days eating no more than 500 calories. Participants underwent MRI scanning at the time of recruitment and at the end of the 12‐week program. Volumetric analyses were conducted through FreeSurfer 7.1.1 (4), relative regional cerebral blood flow (rCBF) was obtained through ASL‐MRICloud (5), and hindered and restricted diffusion fractions (HF and RF) were calculated through the diffusion basis spectrum imaging (DBSI), representing tissue edema and inflammatory cell infiltration respectivelyResultsSix participants were obese, two were overweight and two had normal weight with an average BMI of 30.3±5.48 kg/m2 across participants. Following 12‐weeks of CR, participants showed an increase in normalized hippocampal volume (p:0.02) compared to those on regular diet. CR also resulted in improved cortical thickness in the bilateral medial orbitofrontal cortices compared to the control group (p:0.014). An average increase in relative perfusion (rCBF) in the bilateral inferior temporal gyri (p:0.02, & p:0.004) and bilateral fusiform gyri (p:0.008 & p:0.002) was observed in participants undergoing CR compared to those on a regular diet at the end of 12‐weeks (Figure 1 and 2). Being on a CR diet was associated with reduced HF and RF in the bilateral inferior longitudinal fasciculi (p:0.04 & p:0.002) indicating reduced edema and cellularity (6).ConclusionCR is associated with alterations in brain’s structure and function in terms of improved volumetric measurements, regional perfusion and reduced tissue inflammation, and hence implicated as a neuroprotective intervention in midlife persons.

The stress-responsive geneGDPGP1/mcp-1regulates neuronal glycogen metabolism and survival

Maladaptive responses to stress might play a role in the sensitivity of neurons to stress. To identify novel cellular responses to stress, we performed transcriptional analysis in acutely stressed mouse neurons, followed by functional characterization in Caenorhabditis elegans. In both contexts, we found that the gene GDPGP1/mcp-1 is down-regulated by a variety of stresses. Functionally, the enzyme GDPGP1/mcp-1 protects against stress. Knockdown of GDPGP1 in mouse neurons leads to widespread neuronal cell death. Loss of mcp-1, the single homologue of GDPGP1 in C. elegans, leads to increased degeneration of GABA neurons as well as reduced survival of animals following environmental stress. Overexpression of mcp-1 in neurons enhances survival under hypoxia and protects against neurodegeneration in a tauopathy model. GDPGP1/mcp-1 regulates neuronal glycogen levels, indicating a key role for this metabolite in neuronal stress resistance. Together, our data indicate that down-regulation of GDPGP1/mcp-1 and consequent loss of neuronal glycogen is a maladaptive response that limits neuronal stress resistance and reduces survival.

Walking speed decline in older adults is associated with elevated pro-BDNF in plasma extracellular vesicles

BackgroundBrain-derived neurotrophic factor (BDNF) is produced by cleavage of proBDNF, and BDNF and proBDNF may play antagonistic roles in nervous system development, learning, memory and neuronal stress resistance. BDNF and proBDNF are present in blood, but the origin and relative contributions of soluble and extracellular vesicle (EV)-associated levels are unknown. MethodsIn this study we used validated immunoassays to measure proBDNF and BDNF levels in plasma, total plasma EVs and a subpopulation of EVs enriched for neuronal origin (expressing the neuronal marker L1CAM) in 150 Baltimore Longitudinal Study of Aging participants with and without decline in walking speed (reflecting aging-associated motor decline). ResultsLevels of BDNF and proBDNF were highest in L1CAM+ EVs. Participants with walking speed decline had higher levels of proBDNF in L1CAM+ EVs compared to non-decliners, but no differences in proBDNF levels in plasma and total EV. ConclusionsOur findings suggest that levels of proBDNF and BDNF in circulating L1CAM+ EVs might be used as biomarkers for conditions involving altered BDNF signaling.

3-Hydroxybutyrate regulates energy metabolism and induces BDNF expression in cerebral cortical neurons.

During fasting and vigorous exercise, a shift of brain cell energy substrate utilization from glucose to the ketone 3-hydroxybutyrate (3OHB) occurs. Studies have shown that 3OHB can protect neurons against excitotoxicity and oxidative stress, but the underlying mechanisms remain unclear. Neurons maintained in the presence of 3OHB exhibited increased oxygen consumption and ATP production, and an elevated NAD+ /NADH ratio. We found that 3OHB metabolism increases mitochondrial respiration which drives changes in expression of brain-derived neurotrophic factor (BDNF) in cultured cerebral cortical neurons. The mechanism by which 3OHB induces Bdnf gene expression involves generation of reactive oxygen species, activation of the transcription factor NF-κB, and activity of the histone acetyltransferase p300/EP300. Because BDNF plays important roles in synaptic plasticity and neuronal stress resistance, our findings suggest cellular signaling mechanisms by which 3OHB may mediate adaptive responses of neurons to fasting, exercise, and ketogenic diets.

Mitochondrial SIRT3 Mediates Adaptive Responses of Neurons to Exercise and Metabolic and Excitatory Challenges

The impact of mitochondrial protein acetylation status on neuronal function and vulnerability to neurological disorders is unknown. Here we show that the mitochondrial protein deacetylase SIRT3 mediates adaptive responses of neurons to bioenergetic, oxidative, and excitatory stress. Cortical neurons lacking SIRT3 exhibit heightened sensitivity to glutamate-induced calcium overload and excitotoxicity and oxidative and mitochondrial stress; AAV-mediated Sirt3 gene delivery restores neuronal stress resistance. In models relevant to Huntington's disease and epilepsy, Sirt3(-/-) mice exhibit increased vulnerability of striatal and hippocampal neurons, respectively. SIRT3 deficiency results in hyperacetylation of several mitochondrial proteins, including superoxide dismutase 2 and cyclophilin D. Running wheel exercise increases the expression of Sirt3 in hippocampal neurons, which is mediated by excitatory glutamatergic neurotransmission and is essential for mitochondrial protein acetylation homeostasis and the neuroprotective effects of running. Our findings suggest that SIRT3 plays pivotal roles in adaptive responses of neurons to physiological challenges and resistance to degeneration.

Trans-Resveratrol as A Neuroprotectant

Epidemiological evidence indicates that nutritionally-derived polyphenols such as resveratrol (RES) have neuroprotective properties. Administration of RES to culture media protects a wide variety of neuronal cell types from stress-induced death. Dietary supplementation of RES can ameliorate neuronal damage and death resulting from both acute and chronic stresses in rodents. The specific molecular mechanisms by which RES acts at the cellular level remain incompletely understood. However, many experimental data indicate that RES reduces or prevents the occurrence of oxidative damage. Here we discuss possible mechanisms by which RES might exert protection against oxidative damage and cell death. Evidence suggesting that RES’s chemical antioxidant potential is not sufficient explanation for its effects is discussed. Putative biological activities, including interactions with estrogen receptors and sirtuins are critically discussed. We provide a synthesis of how RES’s phytoestrogenic properties might mediate the neuronal stress resistance underlying its observed neuroprotective properties.