Coexistance of different damage-associated myeloid populations in the hippocampus of Alzheimer's patients

Parenchymal microglia are the brain-resident immune cells capable of responding to damage. Though the role of microglial cells in the development/progression of AD is still unknown, a dysfunctional response has recently gained support since the identification of genetic risk factors related to microglial. In this sense, we reported an attenuated microglial activation in the hippocampus of AD patients, including a degenerative process of the microglial population in the dentate gyrus. On the other hand, it is also known that others myeloid components could also be involved in the neurodegenerative process. However, the implication of the diverse immune cells in the human pathology have not been determined yet. In this work, we analyzed the phenotypic profile displayed by damage-associated myeloid cells in the hippocampus of AD brains. For this purpose, immunohistochemistry and image analysis approaches have been carried out in non-demented controls and AD cases. Damage-associated myeloid cells from Braak II and Braak VI individuals were clustered around amyloid plaques and expressed Iba1, TMEM119, CD68, Trem2 and CD45high. A subset of these cells also expressed ferritin. However, and even though some Braak II individuals accumulated CD45-positive plaques, only AD patients exhibited parenchymal infiltration of CD163-positive cells, along with a decrease of the resident microglial marker TMEM119. Moreover, a negative correlation was observed between CD163 and TMEM119 intensities in Braak VI patients, showing a functional cooperation among these different myeloid populations. Taken together, these findings suggest the existence of different populations of amyloid-associated myeloid cells in the hippocampus during disease progression. The differential contribution of these myeloid populations to the pathogenesis remains to be elucidated. The dynamic of the myeloid molecular phenotypes associated to AD pathology needs to be considered for guarantee clinical success.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Understanding microglial responses in the frontal cortex of alzheimer´s disease patients

Microglial cells, the immune cells of the brain, and the neuroinflammatory process associated, have been postulated as a critical factor in AD pathogenesis, since the identification of genetic risk factors related to microglial function. However, the microglial role in the development/progression of AD has not been determined yet. In this sense, we have previously reported a limited activation and microglial degeneration in the hippocampus of AD patients in contrast to the proinflammatory view based on findings in amyloidogenic models. Here, we have further analyzed the functional/phenotypic profile displayed by microglial cells in other vulnerable brain region of AD patients, the frontal cortex. Immunohistochemistry and image analysis approaches were performed in the frontal cortex of post mortem samples from controls (Braak 0-II) and AD patients (Braak V-VI) including familial cases. Microglia of Braak V-VI individuals were observed forming clusters and showed, both plaque (Iba1+/TMEM119+/P2ry12-/CD45high/Trem2+) and inter-plaque (Iba1+/ TMEM119+/P2ry12-/CD45high/Trem2-) microglial activation, similar that observed in amyloidogenic mice. By contrast, homeostatic and ramified microglial cells of non-demented Braak II cases presented Iba1+/P2ry12+/TMEM119+/CD45low/Trem2- profile. Furthermore, different microglial responses were observed between sporadic and familial AD cases. These different microglial phenotypes associated with AD pathology show the heterogeneity and complexity of the microglial phenotypes and suggest different functional states of these glial cells in a region-specific manner. These data need to be considered for better understand the immunological mechanisms underlying AD progression. Modulating brain inflammatory responses might be a promising avenue to prevent cognitive dysfunction in AD patients. ISCiii:PI18/01557(AG)-PI18/01556(JV);Junta Andalucia:UMA18-FEDERJA211(AG). All cofinanced by FEDER funds (European-Union).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Lithium, as a neuroprotective therapy for Alzheimer’s disease pathology, modifies abeta plaque toxicity

BACKGROUND: Despite the relatively large information about the Alzheimer’s disease (AD) pathology, no effective disease-modifying treatment has been yet developed. Lithium, a primary drug to treat bipolar disorder, has been suggested as a potential treatment against AD. In this work we have evaluated whether lithium treatment could ameliorate the neuropathology progression of the transgenic PS1M146L/APPSwe-London mice. Unlike most transgenic animal models, which do not exhibit the neurodegenerative spectrum of disease observed in the patient population, this AD model exhibits a prominent amyloid pathology along with a selective and significant neuronal loss in the hippocampus and entorhinal cortex. Therefore, this model is highly valuable for evaluating the effectiveness of potential neuroprotective therapies for AD. METHODS: For lithium treatment, PS1/APP mice (3 month old at the beginning of treatment) were fed, ad libitum, with diet supplemented with lithium carbonate (1.2g/kg, Harlan, Spain). The treatment lasts 6 months. After behavioural studies, mice were anesthetized and brains dissected out (hippocampus and cortex). Hemibrains were processed for immunohistochemistry, stereological and image analysis quantification, and the other hemibrains for RT-PCR and Western blot studies. RESULTS: Our data demonstrate that chronic oral administration of lithium, before the pathology onset, resulted in less toxic plaque formation that significantly ameliorated the degenerative processes and behavioural/memory deficits occurring during disease progression in our PS1/APP model. Specifically, and of great relevance for AD prevention, early lithium intervention was able to arrest neuronal loss in hippocampus and entorhinal cortex of highly vulnerable populations. Besides, lithium reduced the axonal dystrophic pathology, associated to amyloid plaques, by increasing the Abeta compaction. Moreover, a significant lower accumulation of phospho-tau, LC3-II and ubiquitinated proteins was detected. Our study highlights that the switch of plaque quality by lithium could be mediated by astrocyte activation and the release of heat shock proteins, which concentrated in the core of the plaques.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Microtubule stabilization reduces amyloid pathology and improves synaptic/memory deficits in APP/PS1 mice

Aims: Cognitive decline in Alzheimer's disease (AD) is highly related to synaptic/neuronal loss. Tau hyperphosphorylation destabilizes microtubules leading to axonal transport failure and generation of dystrophic neurites, thus contributing to synaptic dysfunction. The effect of microtubule stabilization on amyloid-beta pathology has not been assessed in vivo yet. This study evaluated the effect of the microtubule-stabilizing agent, Epothilone D (EpoD) in the pathology of an amyloidogenic mouse model. Methods: APP751SL/PS1M146L mice (3-month-old) were treated weekly with intraperitoneal injections of EpoD (2 mg/kg) or vehicle for 3 months. For memory performance, animals were tested on the objectrecognition, Y-maze and Morris water maze. Hippocampal proteinopathies were quantified by image analysis after immunostaining. Somatostatin (SOM)-numerical density was calculated by stereology. APPswe-N2a cells were treated with EpoD 100nM for 12/24 hours. Protein levels were analysed by Western/dot-blot. Results: EpoD-treated mice improved their performance of cognitive tests, while hippocampal phospho-tau and Ab (especially oligomers) accumulation decreased, together with synaptic/neuritic pathology. Remarkably, EpoD exerted a neuroprotective effect on SOM-interneurons, a highly AD-vulnerable GABAergic subpopulation. Conclusions: EpoD improved microtubule dynamics and axonal transport in an AD-like context, reducing tau and Ab accumulation and promoting neuronal and cognitive protection, underlining the cross-talk between cytoskeleton pathology and proteinopathy. Therefore, microtubule-stabilizing drugs could be candidates for slowing AD at both tau and Ab pathologies.Supported by PI18/01557 (to AG) and PI18/01556 (to JV) grants from ISCiii of Spain, co-financed by FEDER funds (European Union), CIBERNED collaborative grant (to AG and JV), and by PPIT.UMA.B1.2017/26 grant (to RSV). Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Ultrastructural evidence of mitochondrial pathology in hippocampal reactive astrocytes of β-amyloidosis Alzheimer’s transgenic mice

Astrocytes, the most abundant non-neuronal cell type in the CNS, play essential roles in brain homeostasis and neuroprotection, including metabolic support, synaptic plasticity, cerebral blood flow and immunity. Many of these activities are highly energy demanding and require large energy input from efficient mitochondria. During the pathogenic process of Alzheimer’s disease (AD), amyloid-beta and phospho-tau pathologies have a detrimental effect on neurons and glial cells, also impairing mitochondrial function. This could negatively affect neuronal stability, compromising ATP production and energy metabolism, leading to a deleterious effect promoting neurodegeneration. Though the mitochondrial dysfunction is thought to be an early event in the pathogenesis of AD, the majority of studies have focused on neurons, and little is known about their functional characteristics in astrocytes. We aim to analyze mitochondrial subcellular features of rective astrocytes in APP/PS1 mice hippocampus by transmission electron microscopy and image analysis. Reactive astrocytes cluster around amyloid plaques and display marked morphological changes. Our results show mitochondrial structural alterations including mitochondrial cristae loss, broken double membrane structure and fragmentation. In addition, an increase in both number and size of mitochondria in this transgenic model compared to age-matched WT mice, was found. Since mitochondrial morphology is directly related to mitochondrial fusion/fission, the ultrastructural pathology of astrocytic mitochondria in this amyloidogenic model suggests dynamics abnormalities in these organelles that might lead to astroglial functional deficits compromising neuronal survival. Deciphering the mechanisms underlying this pathological phenomenon might help for the development of therapeutic interventions targeted to protect/improve astrocytic mitochondrial function and, in consequense, enhace their neuroprotective support to neurons in AD.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech