Aging affects cognition and hippocampal ultrastructure in male Wistar rats

Neuroinflammation increases in old and oldest-old rats except for dura mater meningeal tissue with significant gender differences: a translational perspective

Neuroinflammaging is the nervous system version of inflammaging, the low-grade inflammation that develops with advanced age, aside from active disease or infection. Despite neuroinflammaging has been widely investigated, some important issues still need to be resolved such as the analysis of the extremely old subjects and the evaluation of specific brain areas. On this background, we conducted a study to analyze expression of inflammatory and anti-inflammatory genes in Wistar rats of different ages, including the oldest-old, in different brain regions. We found that pro-inflammatory mediators were generally up-regulated with age in cortex, hippocampus, and striatum, especially in the oldest-old group. Specifically, TNF-α showed an increment in expression with age in striatum, IL-1β and IFN-γ in hippocampus, and MCP-1 in cortex, hippocampus and striatum. Conversely, CX3CL1 and NOS2 showed a significant reduction of expression in the cortex of the oldest-old group. A different situation was observed in dura mater where TNF-α, IL-6, IL-1β, CX3CL1, and MCP-1 expression decreased in the older groups in comparison with the younger groups. With age the anti-inflammatory cytokines IL-4 and IL-10 were down-regulated in cortex, and TGF-β1 in dura mater, while IL-4 was up-regulated in the oldest-old group in hippocampus. Finally, we observed that female brains underwent an age-related increase of pro-inflammatory cytokines expression compared to males, except for striatum, and a general down-regulation of anti-inflammatory cytokines within each age group. Protein validation of selected factors by ELISA tests supported the observed changes. These data may represent a basis for future research about the neurobiology of aging, in particular in the neurodegenerative disorder framework.

Effects of high-intensity chronic noise on spatial memory in male versus female rats

The detrimental effects of high-intensity noise on the auditory system and emotional status, including the induction of anxiety, are well documented. Preclinical as well as epidemiological and clinical studies have solidly established differential responses between males and females to various stressful stimuli, including high-intensity white noise (HIWN). However, whether chronic exposure to noise affects cognitive functions and whether this effect is sex dependent has not been adequately addressed. In this study, we used two cognitive test paradigms, such as the Morris water maze (MWM) and the multi-branch maze (MBM), to test the effect of chronic HIWN on indices of spatial learning and memory in both male and female Wistar rats. Our findings indicate that daily (1 h) exposure to 100 dB of noise for 30 consecutive days induces different task-dependent responses in male versus female rats. For example, in the acquisition phase of MWM, female rats exposed to noise outperformed their male counterparts at twice the speed. Similarly, in the MBM test, noise-exposed female rats outperformed the male rats in reaching the nest box. It is clear from these studies that noise impairs cognitive functions twice as negatively in male rats as in female rats. Thus, sex-related differences in spatial learning and memory in response to HIWN must be taken into consideration when investigating the neurobiological components and/or treatment modalities.

Differential effects of aging on hippocampal ultrastructure in male vs. female rats

Age-related decline in physical and cognitive functions are facts of life that do not affect everyone to the same extent. We had reported earlier that such cognitive decline is both sex- and context-dependent. Moreover, age-associated ultrastructural changes were observed in the hippocampus of male rats. In this study, we sought to determine potential differences in ultrastructural changes between male and female rats at various stages of life. We performed quantitative electron microscopic evaluation of hippocampal CA1 region, an area intimately involved in cognitive behavior, in both male and female adolescent, adult and old Wistar rats. Specifically, we measured the number of docking synaptic vesicles in axo-dendritic synapses, the length of active zone as well as the total number of synaptic vesicles. Distinct age- and sex-dependent effects were observed in several parameters. Thus, adult female rats had the lowest synaptic active zone compared to both adolescent and old female rats. Moreover, the same parameter was significantly lower in adult and old female rats compared to their male counterparts. On the other hand, old male rats had significantly lower number of total synaptic vesicles compared to both adolescent and adult male rats as well as compared to their female counterparts. Taken together, it may be suggested that age- and sex-dependent ultrastructural changes in the hippocampus may underlie at least some of the differences in cognitive functions among these groups.

Expanded bioinformatic analysis of Oximouse dataset reveals key putative processes involved in brain aging and cognitive decline

The theory that aging is driven by the damage produced by reactive oxygen species (ROS) derived from oxidative metabolism dominated geroscience studies during the second half of the 20th century. However, increasing evidence that ROS also plays a key role in the physiological regulation of numerous processes through the reversible oxidation of cysteine residues in proteins, has challenged this notion. Currently, the scope of redox signaling has reached proteomic dimensions through mass spectrometry techniques. Here, we perform a comprehensive bioinformatics analysis of cysteine oxidation changes during mouse brain aging, using the quantitative data provided in the Oximouse dataset. Interestingly, our unbiased analysis identified hundreds of putative cysteine redox switches covering several pathways previously associated with aging. These include the ubiquitin-proteasome pathway and one-carbon metabolism (folate cycle, methionine cycle, transsulfuration and polyamine pathways). Surprisingly, cysteine oxidation changes are enriched in synaptic proteins in a highly asymmetric distribution: while postsynaptic proteins tend to increase cysteine oxidation with age, the opposite occurs for presynaptic proteins. Additionally, cysteine oxidation changes during aging are associated with proteins involved in the regulation of the mitochondrial transition pore opening and synaptic calcium homeostasis. Our analysis reinforces the concept that brain aging is associated with selective changes in the oxidation state of key proteins, rather than an overall trend toward increased oxidation. Also, we provide a prioritized list of specific cysteine residues with putative impact in aging processes for future experimental validation.

Axonal energy metabolism, and the effects in aging and neurodegenerative diseases

Human studies consistently identify bioenergetic maladaptations in brains upon aging and neurodegenerative disorders of aging (NDAs), such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and Amyotrophic lateral sclerosis. Glucose is the major brain fuel and glucose hypometabolism has been observed in brain regions vulnerable to aging and NDAs. Many neurodegenerative susceptible regions are in the topological central hub of the brain connectome, linked by densely interconnected long-range axons. Axons, key components of the connectome, have high metabolic needs to support neurotransmission and other essential activities. Long-range axons are particularly vulnerable to injury, neurotoxin exposure, protein stress, lysosomal dysfunction, etc. Axonopathy is often an early sign of neurodegeneration. Recent studies ascribe axonal maintenance failures to local bioenergetic dysregulation. With this review, we aim to stimulate research in exploring metabolically oriented neuroprotection strategies to enhance or normalize bioenergetics in NDA models. Here we start by summarizing evidence from human patients and animal models to reveal the correlation between glucose hypometabolism and connectomic disintegration upon aging/NDAs. To encourage mechanistic investigations on how axonal bioenergetic dysregulation occurs during aging/NDAs, we first review the current literature on axonal bioenergetics in distinct axonal subdomains: axon initial segments, myelinated axonal segments, and axonal arbors harboring pre-synaptic boutons. In each subdomain, we focus on the organization, activity-dependent regulation of the bioenergetic system, and external glial support. Second, we review the mechanisms regulating axonal nicotinamide adenine dinucleotide (NAD+) homeostasis, an essential molecule for energy metabolism processes, including NAD+ biosynthetic, recycling, and consuming pathways. Third, we highlight the innate metabolic vulnerability of the brain connectome and discuss its perturbation during aging and NDAs. As axonal bioenergetic deficits are developing into NDAs, especially in asymptomatic phase, they are likely exaggerated further by impaired NAD+ homeostasis, the high energetic cost of neural network hyperactivity, and glial pathology. Future research in interrogating the causal relationship between metabolic vulnerability, axonopathy, amyloid/tau pathology, and cognitive decline will provide fundamental knowledge for developing therapeutic interventions.

Identification of a hippocampal lncRNA-regulating network in a natural aging rat model

Background

Dysregulation of long noncoding RNA (lncRNA) expression is related to aging and age-associated neurodegenerative diseases, and the lncRNA expression profile in the aging hippocampus is not well characterized. In the present investigation, the changed mRNAs and lncRNAs were confirmed via deep RNA sequencing. GO and KEGG pathway analyses were conducted to investigate the principal roles of the clearly dysregulated mRNAs and lncRNAs. Subsequently, through the prediction of miRNAs via which mRNAs and lncRNAs bind together, a competitive endogenous RNA network was constructed.

Results

A total of 447 lncRNAs and 182 mRNAs were upregulated, and 385 lncRNAs and 144 mRNAs were downregulated. Real-time reverse transcription-polymerase chain reaction validated the reliability of mRNA and lncRNA sequencing. KEGG pathway and GO analyses revealed that differentially expressed (DE) mRNAs were associated with cell adhesion molecules (CAMs), the p53 signaling pathway (SP), phagosomes, PPAR SP and ECM—receptor interactions. KEGG pathway and GO analyses showed that the target genes of the DE lncRNAs were related to cellular senescence, the p53 signaling pathway, leukocyte transendothelial migration and tyrosine metabolism. Coexpression analyses showed that 561 DE lncRNAs were associated with DE mRNAs. A total of 58 lncRNA–miRNA–mRNA target pairs were confirmed in this lncRNA‒miRNA‒mRNA network, comprising 10 mRNAs, 13 miRNAs and 38 lncRNAs.

Conclusions

We found specific lncRNAs and mRNAs in the hippocampus of natural aging model rats, as well as abnormal regulatory ceRNA networks. Our outcomes help explain the pathogenesis of brain aging and provide direction for further research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-022-00743-7.

Age-Associated Molecular Changes in Human Hippocampus Subfields as Determined by Quantitative Proteomics

The hippocampus demonstrates age-associated changes in functions, neuronal circuitry, and plasticity during various developmental stages. On the contrary, there is a significant knowledge gap on age-associated proteomic alterations in the hippocampus subfields. Using tandem mass tag-based high-resolution mass spectrometry and quantitative proteomics, we report here age-associated changes in the human hippocampus at the subregional level. We used formalin-fixed paraffin-embedded hippocampal tissue sections from a total of 12 healthy individuals, with 3 individuals from each of the 4 different age groups, specifically, 1-10, 21-30, 31-40, and 81-90 years. We found that lysosome and oxidative phosphorylation were the pathways enriched in the 81- to 90-year age group. On the contrray, nervous system development, synaptic plasticity and transmission, messenger RNA (mRNA) splicing, and electron transport chain (ETC) complex-I activity were the enriched biological processes observed in the younger age groups. In a hippocampus subfield context, our topline findings on age-associated proteome changes include altered expression of proteins associated with adult neurogenesis with age in the dentate gyrus and increased expression of immune response-associated proteins with age in certain cornu ammonis sectors of the hippocampus. Signal peptide analysis predicted hippocampal proteins with secretory potential. While these new findings warrant replication in larger study samples, the current data contribute to (1) our understanding of the molecular basis of proteomic changes across various age groups in hippocampus subfields in healthy individuals, and (2) the design and interpretation of future research on the age-associated neurodegenerative disorders.

Anxiety and ultrastructural consequences of chronic mild stress in rats

Detrimental consequences following exposure to severe stress, either acute or chronic are well recognized. Chronic mild stress (CMS) is also a leading cause of emotional distress and neuropsychiatric conditions such as anxiety disorders. However, the neurobiological substrates of the latter, particularly at the ultrastructural levels have not been adequately investigated. In this study, adult male Wistar rats were subjected to 4 h daily mild restraint for 20 days and their behavior in open field and elevated plus maze (EPM) were evaluated 24 h after the last restraint. Anxiety-like behavior was evident in CMS exposed rats by increases in rearing and grooming in the open field and the avoidance of open arms in the EPM. Concomitant ultrastructural alterations such as chromatolysis, agglutination of synaptic vesicles or mitochondrial damage were also observed in the central nucleus of amygdala (CNA), an area intimately involved in emotional and fear response, in CMS exposed rats. These results while confirming detrimental consequences of CMS, also suggest that ultrastructural alterations in CNA may be a basis for CMS-induced anxiety.