Characterization of hippocampal sclerosis of aging and its association with other neuropathologic changes and cognitive deficits in the oldest-old

A pathologic study of Perivascular pTDP-43 Lin bodies in LATE-NC

BACKGROUND

TAR DNA-Binding Protein 43 (TDP-43) pathological inclusions are a distinctive feature in dozens of neurodegenerative pathologies, including limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC). Prior investigations identified vascular-associated TDP-43-positive micro-lesions, known as "Lin bodies," located on or near the brain capillaries of some individuals with LATE-NC. This study aimed to investigate the relationship between the accumulation of Lin bodies and glial cells in LATE-NC and the potential co-localization with ferritin, a protein associated with iron storage. Using multiplexed immunohistochemistry and digital pathology tools, we conducted pathological analyses to investigate the relationship between Lin bodies and glial markers (GFAP for astrocytes, IBA1 for microglia) and ferritin. Analyses were conducted on post-mortem brain tissues collected from individuals with pathologically confirmed Alzheimer's disease neuropathological changes (ADNC) and LATE-NC.

RESULTS

As shown previously, there was a robust association between Lin bodies and GFAP-positive astrocyte processes. Moreover, we also observed Lin bodies frequently co-localizing with ferritin, suggesting a potential link to compromised vascular integrity. Subsequent analyses demonstrated increased astrocytosis near Lin body-positive vessels compared to those without Lin bodies, particularly in ADNC cases. These results suggest that the accumulation of Lin bodies may elicit an increased glial response, particularly among astrocytes, possibly related to impaired vascular integrity.

CONCLUSIONS

Lin bodies are associated with a local reactive glial response. The strong association of Lin bodies with ferritin suggests that the loss of vascular integrity may be either a cause or a consequence of the pTDP-43 pathology. The reactive glia surrounding the affected vessels could further compromise vascular function.

Comprehensive assessment of TDP-43 neuropathology data in the National Alzheimer's Coordinating Center database

TDP-43 proteinopathy is a salient neuropathologic feature in a subset of frontotemporal lobar degeneration (FTLD-TDP), in amyotrophic lateral sclerosis (ALS-TDP), and in limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC), and is associated with hippocampal sclerosis of aging (HS-A). We examined TDP-43-related pathology data in the National Alzheimer's Coordinating Center (NACC) in two parts: (I) availability of assessments, and (II) associations with clinical diagnoses and other neuropathologies in those with all TDP-43 measures available. Part I: Of 4326 participants with neuropathology data collected using forms that included TDP-43 assessments, data availability was highest for HS-A (97%) and ALS (94%), followed by FTLD-TDP (83%). Regional TDP-43 pathologic assessment was available for 77% of participants, with hippocampus the most common region. Availability for the TDP-43-related measures increased over time, and was higher in centers with high proportions of participants with clinical FTLD. Part II: In 2142 participants with all TDP-43-related assessments available, 27% of participants had LATE-NC, whereas ALS-TDP or FTLD-TDP (ALS/FTLD-TDP) was present in 9% of participants, and 2% of participants had TDP-43 related to other pathologies ("Other TDP-43"). HS-A was present in 14% of participants, of whom 55% had LATE-NC, 20% ASL/FTLD-TDP, 3% Other TDP-43, and 23% no TDP-43. LATE-NC, ALS/FTLD-TDP, and Other TDP-43, were each associated with higher odds of dementia, HS-A, and hippocampal atrophy, compared to those without TDP-43 pathology. LATE-NC was associated with higher odds for Alzheimer's disease (AD) clinical diagnosis, AD neuropathologic change (ADNC), Lewy bodies, arteriolosclerosis, and cortical atrophy. ALS/FTLD-TDP was associated with higher odds of clinical diagnoses of primary progressive aphasia and behavioral-variant frontotemporal dementia, and cortical/frontotemporal lobar atrophy. When using NACC data for TDP-43-related analyses, researchers should carefully consider the incomplete availability of the different regional TDP-43 assessments, the high frequency of participants with ALS/FTLD-TDP, and the presence of other forms of TDP-43 pathology.

Limbic-predominant age-related TDP-43 encephalopathy (LATE-NC): Co-pathologies and genetic risk factors provide clues about pathogenesis

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) is detectable at autopsy in more than one-third of people beyond age 85 years and is robustly associated with dementia independent of other pathologies. Although LATE-NC has a large impact on public health, there remain uncertainties about the underlying biologic mechanisms. Here, we review the literature from human studies that may shed light on pathogenetic mechanisms. It is increasingly clear that certain combinations of pathologic changes tend to coexist in aging brains. Although "pure" LATE-NC is not rare, LATE-NC often coexists in the same brains with Alzheimer disease neuropathologic change, brain arteriolosclerosis, hippocampal sclerosis of aging, and/or age-related tau astrogliopathy (ARTAG). The patterns of pathologic comorbidities provide circumstantial evidence of mechanistic interactions ("synergies") between the pathologies, and also suggest common upstream influences. As to primary mediators of vulnerability to neuropathologic changes, genetics may play key roles. Genes associated with LATE-NC include TMEM106B, GRN, APOE, SORL1, ABCC9, and others. Although the anatomic distribution of TDP-43 pathology defines the condition, important cofactors for LATE-NC may include Tau pathology, endolysosomal pathways, and blood-brain barrier dysfunction. A review of the human phenomenology offers insights into disease-driving mechanisms, and may provide clues for diagnostic and therapeutic targets.

Pathologic correlates of aging-related tau astrogliopathy: ARTAG is associated with LATE-NC and cerebrovascular pathologies, but not with ADNC

Age-related tau astrogliopathy (ARTAG) is detectable in the brains of over one-third of autopsied persons beyond age 80, but the pathoetiology of ARTAG is poorly understood. Insights can be gained by analyzing risk factors and comorbid pathologies. Here we addressed the question of which prevalent co-pathologies are observed with increased frequency in brains with ARTAG. The study sample was the National Alzheimer's Coordinating Center (NACC) data set, derived from multiple Alzheimer's disease research centers (ADRCs) in the United States. Data from persons with unusual conditions (e.g. frontotemporal dementia) were excluded leaving 504 individual autopsied research participants, clustering from 20 different ADRCs, autopsied since 2020; ARTAG was reported in 222 (44.0%) of included participants. As has been shown previously, ARTAG was increasingly frequent with older age and in males. The presence and severity of other common subtypes of pathology that were previously linked to dementia were analyzed, stratifying for the presence of ARTAG. In logistical regression-based statistical models that included age and sex as covariates, ARTAG was relatively more likely to be found in brains with limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC), and in brains with comorbid cerebrovascular pathology (arteriolosclerosis and/or brain infarcts). However, ARTAG was not associated with severe Alzheimer's disease neuropathologic change (ADNC), or primary age-related tauopathy (PART). In a subset analysis of 167 participants with neurocognitive testing data, there was a marginal trend for ARTAG pathology to be associated with cognitive impairment as assessed with MMSE scores (P = 0.07, adjusting for age, sex, interval between final clinic visit and death, and ADNC severity). A limitation of the study was that there were missing data about ARTAG pathologies, with incomplete operationalization of ARTAG according to anatomic region and pathologic subtypes (e.g., thorn-shaped or granular-fuzzy astrocytes). In summary, ARTAG was not associated with ADNC, whereas prior observations about ARTAG occurring with increased frequency in aging, males, and brains with LATE-NC were replicated. It remains to be determined whether the increased frequency of ARTAG in brains with comorbid cerebrovascular pathology is related to local infarctions or neuroinflammatory signaling, or with some other set of correlated factors including blood-brain barrier dysfunction.

Cognitive symptoms progress with limbic-predominant age-related TDP-43 encephalopathy stage and co-occurrence with Alzheimer disease

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) is a neuropathologic entity characterized by transactive response DNA-binding protein of 43-kDa (TDP-43)-immunoreactive inclusions that originate in the amygdala and then progress to the hippocampi and middle frontal gyrus. LATE-NC may mimic Alzheimer disease clinically and often co-occurs with Alzheimer disease neuropathologic change (ADNC). This report focuses on the cognitive effects of isolated and concomitant LATE-NC and ADNC. Cognitive/neuropsychological, neuropathologic, genetic, and demographic variables were analyzed in 28 control, 31 isolated LATE-NC, 244 isolated ADNC, and 172 concurrent LATE-NC/ADNC subjects from the National Alzheimer's Coordinating Center. Cases with LATE-NC and ADNC were significantly older than controls; cases with ADNC had a significantly higher proportion of cases with at least one APOE ε4 allele. Both LATE-NC and ADNC exhibited deleterious effects on overall cognition proportional to their neuropathological stages; concurrent LATE-NC/ADNC exhibited the worst overall cognitive effect. Multivariate logistic regression analysis determined an independent risk of cognitive impairment for progressive LATE-NC stages (OR 1.66; p = 0.0256) and ADNC levels (OR 3.41; p < 0.0001). These data add to the existing knowledge on the clinical consequences of LATE-NC pathology and the growing literature on the effects of multiple concurrent neurodegenerative pathologies.

In severe ADNC, hippocampi with comorbid LATE-NC and hippocampal sclerosis have substantially more astrocytosis than those with LATE-NC or hippocampal sclerosis alone

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) and hippocampal sclerosis of aging (HS-A) pathologies are found together at autopsy in ∼20% of elderly demented persons. Although astrocytosis is known to occur in neurodegenerative diseases, it is currently unknown how the severity of astrocytosis is correlated with the common combinations of pathologies in aging brains. To address this knowledge gap, we analyzed a convenience sample of autopsied subjects from the University of Kentucky Alzheimer's Disease Research Center community-based autopsy cohort. The subjects were stratified into 5 groups (n = 51 total): pure ADNC, ADNC + LATE-NC, ADNC + HS-A, ADNC + LATE-NC + HS-A, and low-pathology controls. Following GFAP immunostaining and digital slide scanning with a ScanScope, we measured GFAP-immunoreactive astrocytosis. The severities of GFAP-immunoreactive astrocytosis in hippocampal subfield CA1 and subiculum were compared between groups. The group with ADNC + LATE-NC + HS-A had the most astrocytosis as operationalized by either any GFAP+ or strong GFAP+ immunoreactivity in both CA1 and subiculum. In comparison to that pathologic combination, ADNC + HS or ADNC + LATE-NC alone showed lower astrocytosis. Pure ADNC had only marginally increased astrocytosis in CA1 and subiculum, in comparison to low-pathology controls. We conclude that there appeared to be pathogenetic synergy such that ADNC + LATE-NC + HS-A cases had relatively high levels of astrocytosis in the hippocampal formation.

LATE-NC in Alzheimer's disease: Molecular aspects and synergies

Alzheimer's disease (AD) is classically characterized by senile plaques and neurofibrillary tangles (NFTs). However, multiple copathologies can be observed in the AD brain and contribute to the development of cognitive decline. Limbic-predominant age-related TDP-43 encephalopathy neuropathological changes (LATE-NC) accumulates in the majority of AD cases and leads to more severe cognitive decline compared with AD pathology alone. In this review, we focus on the synergistic relationship between LATE-NC and tau in AD, highlighting the aggravating role of TDP-43 aggregates on tau pathogenesis and its impact on the clinical picture and therapeutic strategies. Additionally, we discuss to what extent the molecular patterns of LATE-NC in AD differ from frontotemporal lobar degeneration with TDP-43 pathology (FTLD-TDP) neuropathological changes. Thus, we highlight the importance of tau and TDP-43 synergies for subtyping AD patients, which may respond differently to therapeutic interventions depending on the presence of comorbid LATE-NC.

Longitudinal hippocampal atrophy in hippocampal sclerosis of aging

Hippocampal sclerosis of aging (HS-A) is a common degenerative neuropathology in older individuals and is associated with dementia. HS-A is characterized by disproportionate hippocampal atrophy at autopsy but cannot be diagnosed during life. Therefore, little is known about the onset and progression of hippocampal atrophy in individuals with HS-A. To better understand the onset and progression of hippocampal atrophy in HS-A, we examined longitudinal hippocampal atrophy using serial MRI in participants with HS-A at autopsy (HS-A+, n = 8) compared to participants with limbic-predominant age-related TDP-43 encephalopathy neuropathological change (LATE-NC) without HS-A (n = 13), Alzheimer's disease neuropathologic change (ADNC) without HS-A or LATE-NC (n = 16), and those without these pathologies (n = 7). We found that participants with HS-A had lower hippocampal volumes compared to the other groups, and this atrophy preceded the onset of dementia. There was also some evidence that rates of hippocampal volume loss were slightly slower in those with HS-A. Together, these results suggest that the disproportionate hippocampal atrophy seen in HS-A may begin early prior to dementia.