Browsing by Author "DeFelipe, Javier"

Hibernating animals have been used as models to study several aspects of the plastic changes that occur in the metabolism and physiology of neurons. These models are also of interest in the study of Alzheimer's disease because the microtubule-associated protein tau is hyperphosphorylated during the hibernation state known as torpor, similar to the pretangle stage of Alzheimer's disease. Hibernating animals undergo torpor periods with drops in body temperature and metabolic rate, and a virtual cessation of neural activity. These processes are accompanied by morphological and neurochemical changes in neurons, which reverse a few hours after coming out of the torpor state. Since tau has been implicated in the structural regulation of the neuronal Golgi apparatus (GA) we have used Western Blot and immunocytochemistry to analyze whether the GA is modified in cortical neurons of the Syrian hamster at different hibernation stages. The results show that, during the hibernation cycle, the GA undergo important structural changes along with differential modifications in expression levels and distribution patterns of Golgi structural proteins. These changes were accompanied by significant transitory reductions in the volume and surface area of the GA elements during torpor and arousal stages as compared with euthermic animals.

Pyramidal neurons are the most common cell type and are considered the main output neuron in most mammalian forebrain structures. In terms of function, differences in the structure of the dendrites of these neurons appear to be crucial in determining how neurons integrate information. To further shed light on the structure of the human pyramidal neurons we investigated the geometry of pyramidal cells in the human and mouse CA1 region—one of the most evolutionary conserved archicortical regions, which is critically involved in the formation, consolidation, and retrieval of memory. We aimed to assess to what extent neurons corresponding to a homologous region in different species have parallel morphologies. Over 100 intracellularly injected and 3D-reconstructed cells across both species revealed that dendritic and axonal morphologies of human cells are not only larger but also have structural differences, when compared to mouse. The results show that human CA1 pyramidal cells are not a stretched version of mouse CA1 cells. These results indicate that there are some morphological parameters of the pyramidal cells that are conserved, whereas others are species-specific.

The search for biomarkers for the early diagnosis of neurodegenerative diseases is a growing area. Numerous investigations are exploring minimally invasive and cost-effective biomarkers, with the detection of phosphorylated Tau (pTau) protein emerging as one of the most promising fields. pTau is the main component of the paired helical filaments found in the brains of Alzheimer’s disease cases and serves as a precursor in the formation of neurofibrillary tangles (NFTs). Recent research has revealed that analysis of p-Tau181, p-Tau217 and p-Tau231 in blood may be an option for detecting the preclinical stage of Alzheimer’s disease. In this study, we have analyzed the values of pTau 181 in the serum of Syrian hamsters during hibernation. Naturally, over the course of hibernation, these animals exhibit a reversible accumulation of pTau in the brain tissue, which rapidly disappears upon awakening. A biosensing system based on the interferometric optical detection method was used to measure the concentration of pTau181 protein in serum samples from Syrian hamsters. This method eliminates the matrix effect and amplifies the signal obtained by using silicon dioxide nanoparticles (SiO2 NPs) biofunctionalized with the αpTau181 antibody. Our results indicate a substantial increase in the serum concentration of pTau in threonine-181 during hibernation, which disappears completely 2–3 h after awakening. Investigating the mechanism by which pTau protein appears in the blood non-pathologically may enhance current diagnostic techniques. Furthermore, since this process is reversible, and no tangles are detected in the brains of hibernating hamsters, additional analysis may contribute to the discovery of improved biomarkers. Additionally, exploring drugs targeting pTau to prevent the formation of tangles or studying the outcomes of any pTau-targeted treatment could be valuable.

Tau has a wide variety of essential functions in the brain, but this protein also plays a determining role in the development of Alzheimer's disease (AD) and other neurodegenerative diseases called tauopathies. This is due to its abnormal aggregation and the subsequent formation of neurofibrillary tangles. Tau hyperphosphorylation appears to be a critical step in its transformation into an aggregated protein. However, the exact process, including the cellular events that trigger it, remains unclear. In this study, we employed immunocytochemistry assays on hippocampal sections from AD cases and from tauopathy cases (Braak stage III) with no evidence of cognitive decline, and the P301S mouse model to investigate the colocalization patterns of Tau phosphorylated (p) at specific residues (S202-T205, S214, and T231) within the proline-rich region. Our results show pyramidal neurons in the hippocampus of P301S mice in which Tau is intensely phosphorylated at residues S202 and T205 (recognized by the AT8 antibody), but with no detectable phosphorylation at S214 or T231. These non-colocalizing neurons displayed intensely labeled aggregated pTau deposits distributed through the soma and dendritic processes. However, most of the hippocampal pyramidal neurons are labeled with pTauS214 or pTauT231 antibodies and typically showed a homogeneous and diffuse pTau distribution (not aggregated). This different labeling likely reflects a Tau conformational step, potentially related to the transition from a diffuse tau phosphorylation phenotype (Type 2) into an NFT-like or Type 1 phenotype. We further observed that dendrites of CA3 pyramidal cells are intensely labeled with pTau214 in the stratum lucidum, but not with AT8 or pTauT231. By contrast, analysis of tissue from AD patients or other human tauopathy cases (Braak stage III) with no evidence of cognitive decline revealed extensive colocalization with both antibody combinations in CA1. The complete or mature tangle development may follow a different mechanism in the P301S mouse model or may require more time to achieve the maturity state found in AD cases. Further studies would be necessary to address this question.

Hibernating mammals undergo torpor periods characterized by a general decrease in body temperature, metabolic rate, and brain activity accompanied by complex adaptive brain changes that appear to protect the brain from extreme conditions of hypoxia and low temperatures. These processes are accompanied by morphological and neurochemical changes in the brain including those in cortical neurons such as the fragmentation and reduction of the Golgi apparatus (GA), which both reverse a few hours after arousal from the torpor state. In the present study, we characterized – by immunofluorescence and confocal microscopy – the GA of cortical astrocytes, oligodendrocytes, and microglial cells in the Syrian hamster, which is a facultative hibernator. We also show that after artificial induction of hibernation, in addition to neurons, the GA of glia in the Syrian hamster undergoes important structural changes, as well as modifications in the intensity of immunostaining and distribution patterns of Golgi structural proteins at different stages of the hibernation cycle.