Towards a Novel Frontier in the Use of Epigenetic Clocks in Epidemiology.

Health problems associated with aging are a major public health concern for the future. Aging is a complex process with wide intervariability among individuals. Therefore, there is a need for innovative public health strategies that target factors associated with aging and the development of tools to assess the effectiveness of these strategies accurately. Novel approaches to measure biological age, such as epigenetic clocks, have become relevant. These clocks use non-sequential variable information from the genome and employ mathematical algorithms to estimate biological age based on DNA methylation levels. Therefore, in the present study, we comprehensively review the current status of the epigenetic clocks and their associations across the human phenome. We emphasize the potential utility of these tools in an epidemiological context, particularly in evaluating the impact of public health interventions focused on promoting healthy aging. Our review describes associations between epigenetic clocks and multiple traits across the life and health span. Additionally, we highlighted the evolution of studies beyond mere associations to establish causal mechanisms between epigenetic age and disease. We explored the application of epigenetic clocks to measure the efficacy of interventions focusing on rejuvenation.

Glutamatergic Neurotransmission in Aging and Neurodegenerative Diseases: A Potential Target to Improve Cognitive Impairment in Aging.

Aging is characterized by the decline in many of the individual's capabilities. It has been recognized that the brain undergoes structural and functional changes during aging that are occasionally associated with the development of neurodegenerative diseases. In this sense, altered glutamatergic neurotransmission, which involves the release, binding, reuptake, and degradation of glutamate (Glu) in the brain, has been widely studied in physiological and pathophysiological aging. In particular, changes in glutamatergic neurotransmission are exacerbated during neurodegenerative diseases and are associated with cognitive impairment, characterized by difficulties in memory, learning, concentration, and decision-making. Thus, in the present manuscript, we aim to highlight the relevance of glutamatergic neurotransmission during cognitive impairment to develop novel strategies to prevent, ameliorate, or delay cognitive decline. To achieve this goal, we provide a comprehensive review of the changes reported in glutamatergic neurotransmission components, such as Glu transporters and receptors during physiological aging and in the most studied neurodegenerative diseases. Finally, we describe the current therapeutic strategies developed to target glutamatergic neurotransmission.

GrimAge is elevated in older adults with mild COVID-19 an exploratory analysis.

COVID-19 has been contained; however, the side effects associated with its infection continue to be a challenge for public health, particularly for older adults. On the other hand, epigenetic status contributes to the inter-individual health status and is associated with COVID-19 severity. Nevertheless, current studies focus only on severe COVID-19. Considering that most of the worldwide population developed mild COVID-19 infection. In the present exploratory study, we aim to analyze the association of mild COVID-19 with epigenetic ages (HorvathAge, HannumAge, GrimAge, PhenoAge, SkinAge, and DNAmTL) and clinical variables obtained from a Mexican cohort of older adults. We found that all epigenetic ages significantly differ from the chronological age, but only GrimAge is elevated. Additionally, both the intrinsic epigenetic age acceleration (IEAA) and the extrinsic epigenetic age acceleration (EEAA) are accelerated in all patients. Moreover, we found that immunological estimators and DNA damage were associated with PhenoAge, SkinBloodHorvathAge, and HorvathAge, suggesting that the effects of mild COVID-19 on the epigenetic clocks are mainly associated with inflammation and immunology changes. In conclusion, our results show that the effects of mild COVID-19 on the epigenetic clock are mainly associated with the immune system and an increase in GrimAge, IEAA, and EEAA.

Serum Levels of Glial Fibrillary Acidic Protein Association with Cognitive Impairment and Type 2 Diabetes.

BACKGROUND: Peripheral biomarkers associated with neurocognitive disorders (NCD) have been evaluated in an attempt to improve diagnosis and early detection and potentially even prevent them. Along with increasing age, type 2 diabetes (T2D) increases the risk of central nervous system disorders and cognitive impairment due to the loss of synaptic function. Central damage triggers an astroglial response, increasing the expression of glial fibrillary acidic protein (GFAP), which can be found peripherally when the blood-brain barrier is compromised. AIM OF THE STUDY: To evaluate the value of GFAP as a peripheral biomarker of central dysfunction. METHODS: Serum levels of GFAP were compared between cases of NCD (n = 69) and age-matched controls (n = 69), analyzing the influence of diabetes as contributing factor. RESULTS: We found higher levels of serum GFAP in subjects with NCD compared with the control group (p <0.0001). The receiver operating characteristic (ROC) curve using the GFAP levels showed 65.22% sensitivity and 71.01% specificity (AUC = 0.7608), indicating good performance in the classification of controls and NCD patients. Logistic regression indicated a positive predictive power of 67.50% considering T2D status; adding GFAP levels, the predictive power rises to 71.93%. GFAP levels and T2D could be considered good predictors of NCD risk. CONCLUSIONS: Our findings open the possibility that peripheral GFAP could be used as an objective measurement related, under certain conditions, to central damage; thereby serving as a follow-up marker to refer diabetic patients for appropriate neurological evaluation, which could offer a low cost, minimally invasive strategy to improve the assessment of cognitive affectation and subsequent treatment.

Citrulline supplementation improves spatial memory in a murine model for Alzheimer's disease.

OBJECTIVES: Alzheimer's disease (AD) correlates with the dysfunction of metabolic pathways that translates into neurological symptoms. An arginine deficiency, a precursor of nitric oxide (NO), has been reported for patients with AD. We aimed to evaluate the effect of citrulline oral supplementation on cognitive decline in an AD murine model. METHODS: Three-month citrulline or water supplementation was blindly given to male and female wild-type and 3 × Tg mice with AD trained and tested in the Morris water maze. Cerebrospinal fluid and brain tissue were collected. Ultra-performance liquid chromatography was used for arginine determinations and the Griess method for NO. RESULTS: Eight-month-old male 3 × Tg mice with AD supplemented with citrulline performed significantly better in the Morris water maze task. Arginine levels increased in the cerebrospinal fluid although no changes were seen in brain tissue and only a tendency of increase of NO was observed. CONCLUSIONS: Citrulline oral administration is a viable treatment for memory improvement in the early stages of AD, pointing to NO as a viable, efficient target for memory dysfunction in AD.

Telomere length and oxidative stress variations in a murine model of Alzheimer's disease progression.

Alzheimer's disease (AD) is the most common cause of dementia, and ageing is its major risk factor. Changes in telomere length have been associated with ageing and some degenerative diseases. Our aim was to explore some of the molecular changes caused by the progression of AD in a transgenic murine model (3xTg-AD; B6; 129-Psen1 Tg (APPSwe, tauP301L) 1Lfa). Telomere length was assessed by qPCR in both brain tissue and peripheral blood cells and compared between three age groups: 5, 9 and 13 months. In addition, a possible effect of oxidative stress on telomere length and AD progression was explored. Shorter telomeres were found in blood cells of older transgenic mice compared to younger and wild-type mice but no changes in telomere length in the hippocampus. An increase in oxidative stress with age was found for all strains, but no correlation was found between oxidative stress and shorter telomere length for transgenic mice. Telomere length and oxidative stress are affected by AD progression in the 3xTg-AD murine model. Changes in blood cells are more noticeable than changes in brain tissue, suggesting that systemic changes can be detected early in the disease in this murine model.

BDNF and Tau as biomarkers of severity in multiple sclerosis.

AIM: Determine if serum levels of tau and BDNF can be used as severity biomarkers in multiple sclerosis (MS). PATIENTS & METHODS: Subjects with MS, older than 18 and younger than 55 years old were included; 74 patients with a diagnosis of relapsing-remitting MS, 11 with secondary-progressive MS, and 88 controls were included. Total tau and BDNF were measured by Western blot. RESULTS: Increased tau and decreased BDNF in MS patients compared with controls was found. Total-tau has a peak in relapsing-remitting MS, the second decile of the multiple sclerosis severity score, and in the lowest expanded disability status scale and is no different than controls for secondary-progressive MS patients and the most severe cases of MS. CONCLUSION: BDNF is a good biomarker for diagnosis of MS but not for severity or progression. Tau appears to have a more active role in the progression of MS.

Role of glutamate receptors of central and basolateral amygdala nuclei on retrieval and reconsolidation of taste aversive memory.

There are a number of experiments showing an important involvement of amygdala N-methyl-d-aspartate (NMDA) glutamate receptors on consolidation of conditioned taste aversion (CTA) memory. Interestingly, recent evidence has shown that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors are particularly involved in CTA retrieval. Memory reconsolidation has been proposed as a destabilization and re-stabilization process induced by memory reactivation. We have recently suggested that reconsolidation could be enabled in the absence of retrieval. Hence, we decided to analyze the participation of AMPA and NMDA receptors of the central (CeA) and basolateral amygdala (BLA) in CTA memory retrieval and reconsolidation. To do so, we tested whether administrations of an AMPA receptor blocker (NBQX) or an NMDA receptor blocker (APV) 15 min before a second acquisition trial could have effects on taste aversion. We found that administration of NBQX in the BLA blocked retrieval, whereas APV blocked reconsolidation in the BLA, and consolidation in the CeA. When we administered both NBQX and APV into the BLA before the second acquisition trial, results showed impairment of both retrieval and reconsolidation. These results further support the idea that reconsolidation is independent of retrieval, since retrieval blockade in the BLA did not impair memory reconsolidation. These results suggest that glutamate receptors have different participation on retrieval and reconsolidation of CTA and further support the hypothesis that these two processes could be independent.

Taste aversion memory reconsolidation is independent of its retrieval.

Reconsolidation refers to the destabilization/re-stabilization memory process upon its activation. However, the conditions needed to undergo reconsolidation, as well as its functional significance is quite unclear and a matter of intense investigation. Even so, memory retrieval is held as requisite to initiate reconsolidation. Therefore, in the present work we examined whether transient pharmacological disruption of memory retrieval impedes reconsolidation of stored memory in the widely used associative conditioning task, taste aversion. We found that AMPA receptors inhibition in the amygdala impaired retrieval of taste aversion memory. Furthermore, AMPA receptors blockade impeded retrieval regardless of memory strength. However, inhibition of retrieval did not affect anisomycin-mediated disruption of reconsolidation. These results indicate that retrieval is a dispensable condition to undergo reconsolidation and provide evidence of molecular dissociation between retrieval and activation of memory in the non-declarative memory model taste aversion.

Differential participation of temporal structures in the consolidation and reconsolidation of taste aversion extinction.

The extinction process has been described as the decline in the frequency or intensity of the conditioned response following the withdrawal of reinforcement. Hence, experimental extinction does not reflect loss of the original memory, but rather reflects new learning, which in turn requires consolidation in order to be maintained in the long term. During extinction of conditioned taste aversion (CTA), a taste previously associated with aversive consequences acquires a safe status through continuous presentations of the flavor with no aversive consequence. In addition, reconsolidation has been defined as the labile state of a consolidated memory after its reactivation by the presentation of relevant information. In this study, we analyzed structures from the temporal lobe that could be involved in consolidation and reconsolidation of extinction of CTA by means of new protein synthesis. Our results showed that protein synthesis in the hippocampus (HC), the perirhinal cortex (PR) and the insular cortex (IC) of rats participate in extinction consolidation, whereas the basolateral amygdala plays no part in this phenomenon. Furthermore, we found that inhibition of protein synthesis in the IC in a third extinction trial had an effect on reconsolidation of extinction. The participation of the HC in taste memory has been described as a downmodulator for CTA consolidation, and has been related to a context-taste association. Altogether, these data suggest that extinction of aversive taste memories are subserved by the IC, HC and PR, and that extinction can undergo reconsolidation, a process depending only on the IC.

Simultaneous but not independent anisomycin infusions in insular cortex and amygdala hinder stabilization of taste memory when updated.

Reconsolidation has been described as a process where a consolidated memory returns to a labile state when retrieved. Growing evidence suggests that reconsolidation is, in fact, a destabilization/stabilization process that incorporates updated information to a previously consolidated memory. We used the conditioned taste aversion (CTA) task in order to test this theory. On the first trial, the conditioned stimulus (CS) (saccharin) was associated to the unconditioned stimulus (US) (LiCl injection), and as a result, aversion to saccharin was obtained. The following day, animals were injected with anisomycin in either the insular cortex (IC), central amygdala (CeA), basolateral amygdala (BLA), or simultaneously in IC and CeA or IC and BLA, and a second CTA trial was carried out in which updated information was acquired. Animals were tested 24 h later. When protein synthesis was inhibited in either the IC or CeA, consolidation was affected and previously consolidated memory was unimpaired. However, when both the IC and CeA were simultaneously anisomycin injected, the previously consolidated memory was affected. After repeated association trials, protein synthesis inhibition in the IC and CeA did not have an effect on taste memory. These results suggest that the IC and the CeA are necessary for taste-aversion consolidation, and that both share the previously consolidated memory trace. In addition, our data demonstrated that protein synthesis in either the IC or the CeA suffices to stabilize previously consolidated taste memory when destabilized by incorporation of updated information.

Intrahippocampal anisomycin infusions disrupt previously consolidated spatial memory only when memory is updated.

Reconsolidation has proven to be a common phenomenon relevant to memory processing. However, the functional significance of this process is still a matter of debate. Previous work has shown that reconsolidation is indeed a process by which updated information is integrated, through the synthesis of proteins, to a memory trace. To further analyze the role that updated information plays in retrieved spatial memory susceptibility to disruption, we injected anisomycin bilaterally in the dorsal hippocampus of Wistar rats. Implanted animals were trained for 5 days on the Morris water maze (MWM) task and injected with anisomycin before the third or fifth training session. When memory was assessed a week later, only animals injected on the third training session showed disruption of long-term memory. Furthermore, when animals were trained for either 3 (middle-trained) or 5 (well-trained) days and a week later anisomycin was infused before a reminder session, only middle-trained rats infused with anisomycin showed reduced performance when tested for long-term memory. Finally, animals trained for 5 days and injected with anisomycin 7 days later on an extinction session showed impaired long-term extinction when tested. These results suggest that for spatial memory tasks acquisition of updated information is a necessary feature to undergo this process. We propose that reconsolidation is not an accurate term because it implies that consolidation happens again. This conception does not fit with the evidence; hence, we suggest that updating consolidation is a more descriptive term to refer to this process.