Biological changes associated with healthy versus pathological aging: a symposium review

Decoding the heterogeneity of Alzheimer's disease diagnosis and progression using multilayer networks

Alzheimer's disease (AD) is a multifactorial and heterogeneous disorder, which makes early detection a challenge. Studies have attempted to combine biomarkers to improve AD detection and predict progression. However, most of the existing work reports results in parallel or compares normalized findings but does not analyze data simultaneously. We tested a multi-dimensional network framework, applied to 490 subjects (cognitively normal [CN] = 147; mild cognitive impairment [MCI] = 287; AD = 56) from ADNI, to create a single model capable of capturing the heterogeneity and progression of AD. First, we constructed subject similarity networks for structural magnetic resonance imaging, amyloid-β positron emission tomography, cerebrospinal fluid, cognition, and genetics data and then applied multilayer community detection to find groups with shared similarities across modalities. Individuals were also followed-up longitudinally, with AD subjects having, on average, 4.5 years of follow-up. Our findings show that multilayer community detection allows for accurate identification of present and future AD (≈90%) and is also able to identify cases that were misdiagnosed clinically. From all MCI participants who developed AD or reverted to CN, the multilayer model correctly identified 90.8% and 88.5% of cases respectively. We observed similar subtypes across the full sample and when examining multimodal data from subjects with no AD pathology (i.e., amyloid negative). Finally, these results were also validated using an independent testing set. In summary, the multilayer framework is successful in detecting AD and provides unique insight into the heterogeneity of the disease by identifying subtypes that share similar multidisciplinary profiles of neurological, cognitive, pathological, and genetics information.

Transcriptional features of biological age maintained in human cultured cardiac interstitial cells

Ex vivo expansion of cells is necessary in regenerative medicine to generate large populations for therapeutic use. Adaptation to culture conditions prompt an increase in transcriptome diversity and decreased population heterogeneity in cKit+ cardiac interstitial cells (cCICs). The "transcriptional memory" influenced by cellular origin remained unexplored and is likely to differ between neonatal versus senescent input cells undergoing culture expansion. Transcriptional profiles derived from single cell RNASEQ platforms characterized human cCIC derived from neonatal and adult source tissue. Bioinformatic analysis revealed contrasting imprint of age influencing targets of 1) cell cycle, 2) senescence associated secretory phenotype (SASP), 3) RNA transport, and 4) ECM-receptor/fibrosis. A small subset of cCICs exist in a transcriptional continuum between "youthful" phenotype and the damaged microenvironment of LVAD tissue in which they were embedded. The connate transcriptional phenotypes offer fundamental biological insight and highlights cellular input as a consideration in culture expansion and adoptive transfer protocols.

Implication of post-translationally modified SOD1 in pathological aging

Why certain people relish healthy aging throughout their life span while others suffer pathological consequences? In this review, we focus on some of the dominant paradigms of pathological aging, such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), and Parkinson's disease (PD), and predict that the antioxidant superoxide dismutase 1 (SOD1), when post-translationally modified by aging-associated oxidative stress, acts as a mechanism to accelerated aging in these age-related neurodegenerative diseases. Oxidative modifications of natively reduced SOD1 induce pathological confirmations such as misfolding, leading to a subsequent formation of monomeric, oligomeric, and multimeric aggregates. Misfolded SOD1 propagates like prions from cell to cell. These modified conformations are detected in brain tissues in ALS, AD, and PD, and are considered a contributing factor to their initial pathogenesis. We have also elaborated on oxidative stress-induced non-native modifications of SOD1 and offered a logistic argument on their global implication in accelerated or pathological aging in the context of ALS, AD, and PD.

Manifestations of allostatic load in residents of radiation contaminated areas aged 18–24 years

We studied the features of allostatic load (AL) in 100 students aged 18–24 years old who, from birth to adulthood, lived in the territories assigned to the IV radiation zone after the Chornobyl accident (density of soil contamination by isotopes 137Cs 3.7–18.5∙104 Bq/m2) and underwent prolonged exposure to small doses of ionizing radiation. The examined students did not have any clinical signs of the immune-neuroendocrine system dysfunction. 50 people had signs of vegetative-vascular dystonia syndrome (VVD), 48 had signs of moderate hyperthyroidism and 21 had signs of moderate hypothyroidism. During the examination session, as a factor of additional psycho-emotional load, in 66 of the examined the immunoregulatory index CD4+/CD8+ went below the lower limit of the homeostatic norm, in 62 of the examined low density lipoprotein cholesterol (LDL-C) exceeded the upper level. The relative risk (RR) and attributable risk (AR) of the participation of potential secondary factors of allostatic load formation in CD4+/CD8+ immunoregulatory index going below the lower limit were calculated. The presence of statistically significant relative risk of participation in the formation of suppression of the index CD4+/CD8+: the state of hyperthyroidism, state of hypothyroidism, vegetative-vascular dystonia syndrome, higher than normal LDL-C. When the examined students combined the signs of hyperthyroidism, vegetative-vascular dystonia syndrome and higher level of LDL-C; with combination of signs of hypothyroidism, vegetative-vascular dystonia syndrome and higher level of LDL-C. The attributable risk in all cases exceeded 0.10, which confirmed the importance of some of these factors and their complexes in the formation of the effect of reduced immunoregulatory index. The CD4+/CD8+ index can be considered an important biomarker of AL and premature age-related changes in the immune system in residents of radiation-contaminated areas. The risk of AL formation in the case of occurrence of a complex of mediated secondary biomarkers (vegetative-vascular dystonia syndrome, thyroid dysfunction, hypercholesterolemia) is higher compared to their individual significance.

Evaluation of prognostic indices in elderly hospitalized patients

AIM

Prognosis informs the physician's decision-making process, especially for frail older adults. So far, any non-disease-specific index has proven full evidence for routine use in clinical practice. Here, we aimed at assessing, prospectively, the calibration and discriminating accuracy of validated prognostic indices in a cohort of elderly hospitalized patients.

METHODS

This was a prospective observational study that enrolled elderly patients (n = 100). The patients' assessment included clinical variables, as well as the following five prognostic indices of mortality: (i) Levine index (2007); (ii) Walter index (2001); (iii) CARING (C, primary diagnosis of cancer; A, ≥ 2 admissions to the hospital for a chronic illness within the last year; R, resident in a nursing home; I, intensive care unit admission with multiorgan failure, NG, noncancer hospice guidelines [meeting ≥ 2 of the National Hospice and Palliative Care Organization's guidelines]) criteria of Fischer (2006-2011); (iv) Silver Code of Di Bari (2010); and (v) Burden of Illness Score for Elderly Persons of Inouye (2003).

RESULTS

Patients' clinical characteristics: 70% women (age 86.20 ± 0.69 years), 30% men (age 85.40 ± 1.07 years), Comorbidity Illness rating scale (CIRS) 4.3 ± 0.61 and Barthel Index 28 ± 0.54. Walter and Burden of Illness Score for Elderly Persons scores showed similar prediction rates when compared with the expected validated values (ancova: F = 14.00, P < 0.008). Burden of Illness Score for Elderly Persons was the most calibrated and accurate index (receiver operating characteristic curve 0.72; P < 0.02).

CONCLUSIONS

None of the assessed prognostic indices, in a "real world" scenario, afforded the optimal predictive accuracy (receiver operating characteristic curve 0.90); all these indices are still far from a robust answer to the prognosis in older age, reflecting a poor ability to encompass the spectrum of frailty. Effort should be made to tailor the prognostication in geriatrics, moving from a disease-centered model to a precision model, tailored to the frail phenotype. Geriatr Gerontol Int 2017; 17: 1015-1021.

Association between prefrontal activity and volume change in prefrontal and medial temporal lobes in aging and dementia: a review

Functional neuroimaging studies have consistently reported age-related changes in prefrontal cortex (PFC) activity during a variety of cognitive tasks, including episodic memory. These changes are often interpreted within the context of one of the following three neural models of age-related changes in brain function: dedifferentiation, neural inefficiency, and neural plasticity and compensation models. Distinguishing between these competing models has proven difficult when interpreting results using functional imaging data alone. In this paper we suggest that a more accurate interpretation of age-related changes in PFC activity requires consideration of age-related differences in gray matter volume (GMv) in PFC and the medial temporal lobes (MTL). We review fMRI studies of cognitive aging that have directly examined the relationship between PFC activity and both local (PFC) and distal (MTL) GMv in older versus younger adults. We also considered how structure-function relationships may be further modified in pathological aging (i.e. mild cognitive impairment (MCI) and Alzheimer's disease (AD)). We found that when task performance was matched between age-groups there was a negative association between regional PFC volume and activity in older adults. However, when older adults performed worse than young adults we observed a positive association between volume and activity in right lateral PFC. Additionally during memory tasks, several studies revealed that PFC activity is positively related to GM volume in MTL in healthy older adults, but negatively related in MCI and AD patients. We conclude that PFC activity is related to age-related changes in local and distal GM volume reductions and that consideration of these structural measures aids the interpretation of fMRI results. Furthermore, the study of structure-function relationships may provide important insights into the biological mechanisms underlying healthy versus pathological aging.

Neurofunctional (re)organization underlying narrative discourse processing in aging: evidence from fNIRS

Relatively few studies have analyzed the mechanisms underlying the cognitive changes that affect language in the elderly, and fewer have done so for narrative discourse. The goal of this study was to explore the neurofunctional changes associated with aging for different components of narrative discourse. Functional near-infrared spectroscopy (fNIRS) and behavioral data on 10 younger adults and 10 healthy elderly participants were collected. Ten younger adults in a non-proficient second language condition were included to explore the possibility that the age-related neurofunctional reorganization partly expresses demanding resource allocation. Results show within- and across-hemispheric differences in the neurofunctional pattern of activation in the older participants with reference to the younger ones, partially shared with the low-proficiency young adults, providing support for the recognized mechanisms underlying neural reserve and compensation. fNIRS was shown to be appropriate for studying the age-related neurofunctional reorganization of complex cognitive abilities.

Alexithymia and aging: a neuropsychological perspective

Consistent with the emotional changes associated with later life, higher alexithymia scores are widely reported in older adults, but their significance has not been fully examined. We posited that association between alexithymia and poorer neurocognition would support the deficit nature of alexithymia in later life. Widely used neurocognitive tests assessing the relative integrity of the left and right hemisphere functions were used to examine the extent to which alexithymia of older age is associated with poor left or right hemisphere functioning. Healthy community-dwelling volunteers (20 young and 20 elderly subjects) were studied with the 20-item Toronto Alexithymia Scale. Neurocognitive competence was assessed using a neuropsychological battery measuring attention, language, memory, visuospatial abilities, and executive functions. Neurocognitive abilities were strongly age-related and indirectly correlated with alexithymia. Alexithymia total score appeared to be uniquely predicted by Raven Matrices and Rey's Figure Recall. These results support the deficit hypothesis alexithymia of older age.

Maturation of limbic regions in Asperger syndrome: a preliminary study using proton magnetic resonance spectroscopy and structural magnetic resonance imaging

People with autistic spectrum disorders (ASD, including Asperger syndrome) may have developmental abnormalities in the amygdala-hippocampal complex (AHC). However, in vivo, age-related comparisons of both volume and neuronal integrity of the AHC have not yet been carried out in people with Asperger syndrome (AS) versus controls. We compared structure and metabolic activity of the right AHC of 22 individuals with AS and 22 healthy controls aged 10-50 years and examined the effects of age between groups. We used structural magnetic resonance imaging (sMRI) to measure the volume of the AHC, and magnetic resonance spectroscopy ((1)H-MRS) to measure concentrations of N-acetyl aspartate (NAA), creatine+phosphocreatine (Cr+PCr), myo-inositol (mI) and choline (Cho). The bulk volume of the amygdala and the hippocampus did not differ significantly between groups, but there was a significant difference in the effect of age on the hippocampus in controls. Compared with controls, young (but not older) people with AS had a significantly higher AHC concentration of NAA and a significantly higher NAA/Cr ratio. People with AS, but not controls, had a significant age-related reduction in NAA and the NAA/Cr ratio. Also, in people with AS, but not controls, there was a significant relationship between concentrations of choline and age so that choline concentrations reduced with age. We therefore suggest that people with AS have significant differences in neuronal and lipid membrane integrity and maturation of the AHC.