Dysfunction of the noradrenergic system drives inflammation, α-synucleinopathy, and neuronal loss in mouse colon.

Clinical and pathological evidence revealed that α-synuclein (α-syn) pathology seen in PD patients starts in the gut and spreads via anatomically connected structures from the gut to the brain. Our previous study demonstrated that depletion of central norepinephrine (NE) disrupted brain immune homeostasis, producing a spatiotemporal order of neurodegeneration in the mouse brain. The purpose of this study was 1) to determine the role of peripheral noradrenergic system in the maintenance of gut immune homeostasis and in the pathogenesis of PD and 2) to investigate whether NE-depletion induced PD-like α-syn pathological changes starts from the gut. For these purposes, we investigated time-dependent changes of α-synucleinopathy and neuronal loss in the gut following a single injection of DSP-4 (a selective noradrenergic neurotoxin) to A53T-SNCA (human mutant α-syn) over-expression mice. We found DPS-4 significantly reduced the tissue level of NE and increased immune activities in gut, characterized by increased number of phagocytes and proinflammatory gene expression. Furthermore, a rapid-onset of α-syn pathology was observed in enteric neurons after 2 weeks and delayed dopaminergic neurodegeneration in the substantia nigra was detected after 3-5 months, associated with the appearance of constipation and impaired motor function, respectively. The increased α-syn pathology was only observed in large, but not in the small, intestine, which is similar to what was observed in PD patients. Mechanistic studies reveal that DSP-4-elicited upregulation of NADPH oxidase (NOX2) initially occurred only in immune cells during the acute intestinal inflammation stage, and then spread to enteric neurons and mucosal epithelial cells during the chronic inflammation stage. The upregulation of neuronal NOX2 correlated well with the extent of α-syn aggregation and subsequent enteric neuronal loss, suggesting that NOX2-generated reactive oxygen species play a key role in α-synucleinopathy. Moreover, inhibiting NOX2 by diphenyleneiodonium or restoring NE function by salmeterol (a ß2-receptor agonist) significantly attenuated colon inflammation, α-syn aggregation/propagation, and enteric neurodegeneration in the colon and ameliorated subsequent behavioral deficits. Taken together, our model of PD shows a progressive pattern of pathological changes from the gut to the brain and suggests a potential role of the noradrenergic dysfunction in the pathogenesis of PD.

Spectrally Resolved Fiber Photometry for In Vivo Multi-Color Fluorescence Measurements.

This article describes how to assemble and operate a spectrometer-based fiber photometry system for in vivo simultaneous measurements of multiple fluorescent biosensors in freely moving mice. The first section of the article describes the step-by-step procedure to assemble a basic single-spectrometer fiber photometry system and how to expand it into a dual-spectrometer system that allows for simultaneous recordings from two sites. The second part describes the steps for a typical fiber probe implantation surgery. The last section describes how to acquire and analyze the time-lapsed spectral data. This article is intended for teaching labs how to build their own fiber photometry systems (with a video tutorial) from commercially available parts and perform in vivo recordings in behaving mice. © Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Basic Protocol 1: Assembling a dual-laser, single-spectrometer fiber photometry system Support Protocol: Dual-spectrometer fiber photometry assembly Basic Protocol 2: Optical fiber probe implantation Basic Protocol 3: Data acquisition and analysis.

Spectrally Resolved Fiber Photometry for Multi-component Analysis of Brain Circuits.

To achieve simultaneous measurement of multiple cellular events in molecularly defined groups of neurons in vivo, we designed a spectrometer-based fiber photometry system that allows for spectral unmixing of multiple fluorescence signals recorded from deep brain structures in behaving animals. Using green and red Ca2+ indicators differentially expressed in striatal direct- and indirect-pathway neurons, we were able to simultaneously monitor the neural activity in these two pathways in freely moving animals. We found that the activities were highly synchronized between the direct and indirect pathways within one hemisphere and were desynchronized between the two hemispheres. We further analyzed the relationship between the movement patterns and the magnitude of activation in direct- and indirect-pathway neurons and found that the striatal direct and indirect pathways coordinately control the dynamics and fate of movement. VIDEO ABSTRACT.

Aß induces PUMA activation: a new mechanism for Aß-mediated neuronal apoptosis.

p53 upregulated modulator of apoptosis (PUMA) is a promising tumor therapy target because it elicits apoptosis and profound sensitivity to radiation and chemotherapy. However, inhibition of PUMA may be beneficial for curbing excessive apoptosis associated with neurodegenerative disorders. Alzheimer's disease (AD) is a representative neurodegenerative disease in which amyloid-ß (Aß) deposition causes neurotoxicity. The regulation of PUMA during Aß-induced neuronal apoptosis remains poorly understood. Here, we reported that PUMA expression was significantly increased in the hippocampus of transgenic mice models of AD and hippocampal neurons in response to Aß. PUMA knockdown protected the neurons against Aß-induced apoptosis. Furthermore, besides p53, PUMA transactivation was also regulated by forkhead box O3a through p53-independent manner following Aß treatment. Notably, PUMA contributed to neuronal apoptosis through competitive binding of apoptosis repressor with caspase recruitment domain to activate caspase-8 that cleaved Bid into tBid to accelerate Bax mitochondrial translocation, revealing a novel pathway of Bax activation by PUMA to mediate Aß-induced neuronal apoptosis. Together, we demonstrated that PUMA activation involved in Aß-induced apoptosis, representing a drug target to antagonize AD progression.

Activated ERK/FOXM1 pathway by low-power laser irradiation inhibits UVB-induced senescence through down-regulating p21 expression.

Cellular senescence is a growth-arrest program that limits cell proliferation. Low-power laser irradiation (LPLI) has been demonstrated to promote cell proliferation. However, whether LPLI can inhibit cellular senescence remains unknown. In the present study, to investigate the functional role of LPLI against skin aging, we used ultraviolet radiation b (UVB) to induce cell senescence. We first report that LPLI can delay UVB-induced cell senescence. The senescence-associated ß-galactosidase (SA-ß-Gal) activity and p21 expression, hallmarks of senescent cells, were decreased in the Forkhead box transcription factor FOXM1-dependent manner under treatment with LPLI. The effect of LPLI was further enhanced with an overexpression of FOXM1, and abolished when FOXM1 was knockdown with short hairpin RNA (shRNA). Furthermore, LPLI activated the extracellular regulated protein kinases (ERK) that was upstream of FOXM1. This led to FOXM1 phosphorylation and nuclear translocation. Nuclear translocation enhanced FOXM1 transcriptional activity and promoted its downstream target gene c-Myc expression that could inhibit p21 expression. These findings highlight the protective effects of ERK/FOXM1 pathway against UVB-induced cell senescence, suggesting a potential protecting strategy for treating skin aging by LPLI.

Low-level laser therapy rescues dendrite atrophy via upregulating BDNF expression: implications for Alzheimer's disease.

Downregulation of brain-derived neurotrophic factor (BDNF) in the hippocampus occurs early in the progression of Alzheimer's disease (AD). Since BDNF plays a critical role in neuronal survival and dendrite growth, BDNF upregulation may contribute to rescue dendrite atrophy and cell loss in AD. Low-level laser therapy (LLLT) has been demonstrated to regulate neuronal function both in vitro and in vivo. In the present study, we found that LLLT rescued neurons loss and dendritic atrophy via upregulation of BDNF in both Aß-treated hippocampal neurons and cultured APP/PS1 mouse hippocampal neurons. Photoactivation of transcription factor CRE-binding protein (CREB) increased both BDNF mRNA and protein expression, since knockdown CREB blocked the effects of LLLT. Furthermore, CREB-regulated transcription was in an ERK-dependent manner. Inhibition of ERK attenuated the DNA-binding efficiency of CREB to BDNF promoter. In addition, dendrite growth was improved after LLLT, characterized by upregulation of Rac1 activity and PSD-95 expression, and the increase in length, branching, and spine density of dendrites in hippocampal neurons. Together, these studies suggest that upregulation of BDNF with LLLT by activation of ERK/CREB pathway can ameliorate Aß-induced neurons loss and dendritic atrophy, thus identifying a novel pathway by which LLLT protects against Aß-induced neurotoxicity. Our research may provide a feasible therapeutic approach to control the progression of AD.