Calcium and neuronal cytoskeletal proteins: alterations with aging

Don't die like me: Which proteins are responsible for the selective neuronal vulnerability within the substantia nigra?

A hallmark of Parkinson's disease is the specific degeneration of dopaminergic neurons in the substantia nigra pars compacta. Interestingly, not all of these neurons are affected to the same extent. Studies revealed that neurons located more ventrally within the substantia nigra pars compacta have a higher prevalence to degenerate than those located in the dorsal tier. The underlying reasons for this selective neuronal vulnerability are still unknown. The aim of the present study was to gain a better understanding of molecular differences between these two neuronal subpopulations that may explain the selective neuronal vulnerability within the human substantia nigra. For this purpose, the neurons from the ventral as well as dorsal tier of the substantia nigra were specifically isolated out of neuropathologically unremarkable human substantia nigra sections with laser microdissection. Following, their proteome was analyzed by data independent acquisition mass spectrometry. The samples were analysed donor-specifically and not pooled for this purpose. A total of 5,391 proteins were identified in the substantia nigra. Of these, 2,453 proteins could be quantified in 100% of the dorsal tier samples. 1,629 could be quantified in 100% of the ventral tier samples. Nine proteins were differentially regulated with a log2 value ≥0.5 and a Qvalue ≤0.05. Of these 7 were higher abundant in the dorsal tier and 2 higher in the ventral tier. These proteins are associated with the cytoskeleton, neuronal plasticity, or calcium homeostasis. With these findings a deeper understanding can be gained of the selective neuronal vulnerability within the substantia nigra and of protective mechanisms against neurodegeneration in specific neuronal subpopulations.

Long Non-Coding RNAs in Neuronal Aging

The expansion of long non-coding RNAs (lncRNAs) in organismal genomes has been associated with the emergence of sophisticated regulatory networks that may have contributed to more complex neuronal processes, such as higher-order cognition. In line with the important roles of lncRNAs in the normal functioning of the human brain, dysregulation of lncRNA expression has been implicated in aging and age-related neurodegenerative disorders. In this paper, we discuss the function and expression of known neuronal-associated lncRNAs, their impact on epigenetic changes, the contribution of transposable elements to lncRNA expression, and the implication of lncRNAs in maintaining the 3D nuclear architecture in neurons. Moreover, we discuss how the complex molecular processes that are orchestrated by lncRNAs in the aged brain may contribute to neuronal pathogenesis by promoting protein aggregation and neurodegeneration. Finally, this review explores the possibility that age-related disturbances of lncRNA expression change the genomic and epigenetic regulatory landscape of neurons, which may affect neuronal processes such as neurogenesis and synaptic plasticity.

Parallel high throughput neuronal toxicity assays demonstrate uncoupling between loss of mitochondrial membrane potential and neuronal damage in a model of HIV-induced neurodegeneration

Neurocognitive deficits seen in HIV-associated neurocognitive disorders (HANDs) are attributed to the release of soluble factors from CNS-resident, HIV-infected and/or activated macrophages and microglia. To study HIV-associated neurotoxicity, we used our in vitro model in which primary rat neuronal/glial cultures are treated with supernatants from cultured human monocyte-derived macrophages, infected with a CNS-isolated HIV-1 strain (HIV-MDM). We found that neuronal damage, detected as a loss of microtubule-associated protein-2 (MAP2), begins as early as 2h and is preceded by a loss of mitochondrial membrane potential (Δψ(m)). Interestingly, inhibitors of calpains, but not inhibitors of caspases, blocked MAP2 loss, however neither type of inhibitor prevented the loss of Δψ(m). To facilitate throughput for these studies, we refined a MAP2 cell-based-ELISA whose data closely compare with our standardized method of hand counting neurons. In addition, we developed a tetramethyl rhodamine methyl ester (TMRM)-based multi-well fluorescent plate assay for the evaluation of whole culture Δψ(m). Together, these findings indicate that calpain activation and loss of Δψ(m) may be parallel pathways to death in HIV-MDM-treated neurons and also demonstrate the validity of plate assays for assessing multiple experimental parameters as is useful for screening neurotherapeutics for neuronal damage and death.

Dysregulation of calcium homeostasis in Alzheimer's disease

The accumulation of oligomeric species of beta-amyloid protein in the brain is considered to be a key factor that causes Alzheimer's disease (AD). However, despite many years of research, the mechanism of neurotoxicity in AD remains obscure. Recent evidence strongly supports the theory that Ca2+ dysregulation is involved in AD. Amyloid proteins have been found to induce Ca2+ influx into neurons, and studies on transgenic mice suggest that this Ca2+ influx may alter neuronal excitability. The identification of a risk factor gene for AD that may be involved in the regulation of Ca2+ homeostasis and recent findings which suggest that presenilins may be involved in the regulation of intracellular Ca2+ stores provide converging lines of evidence that support the idea that Ca2+ dysregulation is a key step in the pathogenesis of AD.

Involvement of microtubules in modifications associated with cellular aging

Microtubules are ubiquitous cellular components involved in the control of cell structure and functions, such as cell division, regulation of shape and polarity, intracellular transport, etc. Consequently, any alteration affecting them in structure or function has a good chance of affecting the cell and generally leads to cell dysfunctions. This has been shown for instance, after treatment with microtubule-interacting drugs. Cellular aging is also characterized by the appearance of various cell dysfunctions, but the possible involvement of the microtubules in the aging process, although a rather tempting hypothesis, has not yet been extensively investigated. In this paper, I will first rapidly review the different components that build, organize and control the microtubules in normal cells, independently of the aging process. I will then consider the possible involvement of the microtubules in the aging process, more particularly in models of cells aging in vitro and in aging neuronal cells, which have been the most extensively investigated. There is some evidence for alterations in the microtubule organization both in cells aging in vitro and in the aging brain. But the interpretation of these data awaits further experiments, taking into account the latest progress in tubulin genetics and in microtubule biochemistry. Microtubules could also represent one of the cellular targets affected after signal transduction and could thus be involved in the resulting cellular responses. This hypothesis will be discussed, as it offers new insights into the regulation of microtubule organization, dynamics and functions in normal cells, which will be worthwhile to investigate during the aging process.