Thursday, November 21, 2024
11/21/2024
Recent emergent interest and progress in studying polyamines (PAs) demonstrate that PAs are key players in Alzheimer’s, Huntington’s and Parkinson diseases and several syndromes as well as in aging and HIV associated neurocognitive disorder (HAND). PAs are released in whole brain from internal sources during neuronal activity and trauma. Since PA content declines with aging, the neuroprotection afforded by PAs can decline as well. This substantially increases the risk of morbidity and mortality. Intriguingly, PA content is increasing in pathology and we hypothesize that it may be a kind of protective response. Indeed, dietary spermidine (SD) is neuroprotective against aging, neurotoxicity, cognitive decline, brain injury and increases lifespan. During the previous R15 supported study, we showed that different glial cells, but not neurons, preferentially accumulate PAs in healthy adult brain1 and retina2 and PAs are released by glial specific treatments3. We further found that acetylated spermine (aSP) preliminary data and SP4 open connexin-43 (Cx43) gap junctions (GJs) in astrocytes, however it is unknown if Cx43 hemichannels (HCs) are also opened by PAs. Therefore, PAs as novel “gliomediators” open Cx43 GJs and keep glial syncytium integrity, isopotentiality and may help to hold healthy brain status. Astrocytes convert PAs partially to GABA that is released to regulate synaptic activity5. In addition, we showed that biotinylated SP is taken up by astrocytes via transporters and released via large Cx43 HCs pores6, but it does not permeate from blood to brain7 suggesting uniquely internal PA exchange in the CNS. Using a variety of novel sensors, we observed uptake and release of PAs in astrocytes. We measured both tonic and vesicular SP release from astrocytes and showed that extracellular [SP]o reaches over 100 μM in response to brain ischemia; a concentration sufficient to affect many receptors and channels in both neurons and glia. Our overall hypothesis is that PAs: (1) are taken up by and (2) stored in astrocytes where PAs (3) promote opening of GJs and (4) facilitate transfer of selective molecules4 through GJ channels between astrocytes in the astrocytic syncytium. During glial activation, (5) PAs are liberated and (6) modulate neuronal receptors and channels preliminary data. Such intercellular exchange of PAs has critical effects controlling glial and consequently neuronal networks. Despite its public health importance, relatively little is known about the mechanisms of PA fluxes in glial cells which accumulate PAs. Remaining questions include: (i) Is PA accumulation in glia due to synthesis or Is there a high affinity PA transport in glial cells as an alternative to low affinity pathways? (AIM-1), (ii) What are the mechanisms of glial PA influx and efflux? and (iii) What are the consequences of PA release on interneuron function? (AIM-2). The studies will lead to new scientific knowledge and research opportunities for graduate students to further understand neurodegenerative and neuroprotection processes.
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