Electrophysiological and Imaging Calcium Biomarkers of Aging in Male and Female 5×FAD Mice

The impact of neuroinflammation on neuronal integrity

Neuroinflammation, characterized by a complex interplay among innate and adaptive immune responses within the central nervous system (CNS), is crucial in responding to infections, injuries, and disease pathologies. However, the dysregulation of the neuroinflammatory response could significantly affect neurons in terms of function and structure, leading to profound health implications. Although tremendous progress has been made in understanding the relationship between neuroinflammatory processes and alterations in neuronal integrity, the specific implications concerning both structure and function have not been extensively covered, with the exception of perspectives on glial activation and neurodegeneration. Thus, this review aims to provide a comprehensive overview of the multifaceted interactions among neurons and key inflammatory players, exploring mechanisms through which inflammation influences neuronal functionality and structural integrity in the CNS. Further, it will discuss how these inflammatory mechanisms lead to impairment in neuronal functions and architecture and highlight the consequences caused by dysregulated neuronal functions, such as cognitive dysfunction and mood disorders. By integrating insights from recent research findings, this review will enhance our understanding of the neuroinflammatory landscape and set the stage for future interventions that could transform current approaches to preserve neuronal integrity and function in CNS-related inflammatory conditions.

Biomarker evidence of early vision and rod energy-linked pathophysiology benefits from very low dose DMSO in 5xFAD mice

Here, we test whether early visual and OCT rod energy-linked biomarkers indicating pathophysiology in nicotinamide nucleotide transhydrogenase (Nnt)-null 5xFAD mice also occur in Nnt-intact 5xFAD mice and whether these biomarkers can be pharmacologically treated. Four-month-old wild-type or 5xFAD C57BL/6 substrains with either a null (B6J) Nnt or intact Nnt gene (B6NTac) and 5xFAD B6J mice treated for one month with either R-carvedilol + vehicle or only vehicle (0.01% DMSO) were studied. The contrast sensitivity (CS), external limiting membrane-retinal pigment epithelium (ELM-RPE) thickness (a proxy for low pH-triggered water removal), profile shape of the hyperreflective band just posterior to the ELM (i.e., the mitochondrial configuration within photoreceptors per aspect ratio [MCP/AR]), and retinal laminar thickness were measured. Both wild-type substrains showed similar visual performance indices and dark-evoked ELM-RPE contraction. The lack of a light-dark change in B6NTac MCP/AR, unlike in B6J mice, is consistent with relatively greater mitochondrial efficiency. 5xFAD B6J mice, but not 5xFAD B6NTac mice, showed lower-than-WT CS. Light-adapted 5xFAD substrains both showed abnormal ELM-RPE contraction and greater-than-WT MCP/AR contraction. The inner retina and superior outer retina were thinner. Treating 5xFAD B6J mice with R-carvedilol + DMSO or DMSO alone corrected CS and ELM-RPE contraction but not supernormal MCP/AR contraction or laminar thinning. These results provide biomarker evidence for prodromal photoreceptor mitochondrial dysfunction/oxidative stress/oxidative damage, which is unrelated to visual performance, as well as the presence of the Nnt gene. This pathophysiology is druggable in 5xFAD mice.

The mechanisms to dispose of misfolded proteins in the endoplasmic reticulum of adipocytes

Endoplasmic reticulum (ER)-associated degradation (ERAD) and ER-phagy are two principal degradative mechanisms for ER proteins and aggregates, respectively; however, the crosstalk between these two pathways under physiological settings remains unexplored. Using adipocytes as a model system, here we report that SEL1L-HRD1 protein complex of ERAD degrades misfolded ER proteins and limits ER-phagy and that, only when SEL1L-HRD1 ERAD is impaired, the ER becomes fragmented and cleared by ER-phagy. When both are compromised, ER fragments containing misfolded proteins spatially coalesce into a distinct architecture termed Coalescence of ER Fragments (CERFs), consisted of lipoprotein lipase (LPL, a key lipolytic enzyme and an endogenous SEL1L-HRD1 substrate) and certain ER chaperones. CERFs enlarge and become increasingly insoluble with age. Finally, we reconstitute the CERFs through LPL and BiP phase separation in vitro, a process influenced by both redox environment and C-terminal tryptophan loop of LPL. Hence, our findings demonstrate a sequence of events centered around SEL1L-HRD1 ERAD to dispose of misfolded proteins in the ER of adipocytes, highlighting the profound cellular adaptability to misfolded proteins in the ER in vivo.

L-type calcium channel antagonist isradipine age-dependently decreases plaque associated dystrophic neurites in 5XFAD mouse model

Epidemiological studies suggest that L-type calcium channel (LTCC) antagonists may reduce the incidence of age-associated neurodegenerative diseases including Alzheimer's disease (AD). However, the neuroprotective mechanism of LTCC antagonists is unknown. Amyloid-β (Aβ) pathology disrupts intracellular calcium signaling, which regulates lysosomes and microglial responses. Neurons near Aβ plaques develop dystrophic neurites, which are abnormal swellings that accumulate lysosomes. Further, microglia accumulate around Aβ plaques and secrete inflammatory cytokines. We hypothesized that antagonism of LTCCs with isradipine would reduce Aβ plaque-associated dystrophic neurites and inflammatory microglia in the 5XFAD mouse model by restoring normal intracellular calcium regulation. To test this hypothesis, we treated 6- and 9-month-old 5XFAD mice with isradipine and tested behavior, examined Aβ plaques, microglia, and dystrophic neurites. We found that isradipine treatment age-dependently reduces dystrophic neurites and leads to trending decreases in Aβ but does not modulate plaque associated microglia regardless of age. Our findings provide insight into how antagonizing LTCCs alters specific cell types in the Aβ plaque environment, providing valuable information for potential treatment targets in future AD studies.

Multiple Bioenergy-Linked OCT Biomarkers Suggest Greater-Than-Normal Rod Mitochondria Activity Early in Experimental Alzheimer's Disease

Purpose

In Alzheimer's disease, central brain neurons show evidence for early hyperactivity. It is unclear if this occurs in the retina, another disease target. Here, we tested for imaging biomarker manifestation of prodromal hyperactivity in rod mitochondria in vivo in experimental Alzheimer's disease.

Methods

Light- and dark-adapted 4-month-old 5xFAD and wild-type (WT) mice, both on a C57BL/6J background, were studied with optical coherence tomography (OCT). We measured the reflectivity profile shape of the inner segment ellipsoid zone (EZ) as a proxy for mitochondria distribution. Two additional indices responsive to mitochondria activity were also measured: the thickness of the external limiting membrane-retinal pigment epithelium (ELM-RPE) region and the signal magnitude of a hyporeflective band (HB) between photoreceptor tips and apical RPE. Retinal laminar thickness and visual performance were evaluated.

Results

In response to low energy demand (light), WT mice showed the expected elongation in EZ reflectivity profile shape, relatively thicker ELM-RPE, and greater HB signal. Under high energy demand (dark), the EZ reflectivity profile shape was rounder, the ELM-RPE was thinner, and the HB was reduced. These OCT biomarker patterns for light-adapted 5xFAD mice did not match those of light-adapted WT mice but rather that of dark-adapted WT mice. Dark-adapted 5xFAD and WT mice showed the same biomarker pattern. The 5xFAD mice exhibited modest nuclear layer thinning and lower-than-normal contrast sensitivity.

Conclusions

Results from three OCT bioenergy biomarkers raise the novel possibility of early rod hyperactivity in vivo in a common Alzheimer's disease model.

The STIM1/2-Regulated Calcium Homeostasis Is Impaired in Hippocampal Neurons of the 5xFAD Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of age-related dementia. Neuronal calcium homeostasis impairment may contribute to AD. Here we demonstrated that voltage-gated calcium (VGC) entry and store-operated calcium (SOC) entry regulated by calcium sensors of intracellular calcium stores STIM proteins are affected in hippocampal neurons of the 5xFAD transgenic mouse model. We observed excessive SOC entry in 5xFAD mouse neurons, mediated by STIM1 and STIM2 proteins with increased STIM1 contribution. There were no significant changes in cytoplasmic calcium level, endoplasmic reticulum (ER) bulk calcium levels, or expression levels of STIM1 or STIM2 proteins. The potent inhibitor BTP-2 and the FDA-approved drug leflunomide reduced SOC entry in 5xFAD neurons. In turn, excessive voltage-gated calcium entry was sensitive to the inhibitor of L-type calcium channels nifedipine but not to the T-type channels inhibitor ML218. Interestingly, the depolarization-induced calcium entry mediated by VGC channels in 5xFAD neurons was dependent on STIM2 but not STIM1 protein in cells with replete Ca²⁺ stores. The result gives new evidence on the VGC channel modulation by STIM2. Overall, the data demonstrate the changes in calcium signaling of hippocampal neurons of the AD mouse model, which precede amyloid plaque accumulation or other signs of pathology manifestation.

Monoclonal antibody-mediated immunosuppression enables long-term survival of transplanted human neural stem cells in mouse brain

BACKGROUND

As the field of stem cell therapy advances, it is important to develop reliable methods to overcome host immune responses in animal models. This ensures survival of transplanted human stem cell grafts and enables predictive efficacy testing. Immunosuppressive drugs derived from clinical protocols are frequently used but are often inconsistent and associated with toxic side effects. Here, using a molecular imaging approach, we show that immunosuppression targeting costimulatory molecules CD4 and CD40L enables robust survival of human xenografts in mouse brain, as compared to conventional tacrolimus and mycophenolate mofetil.

METHODS

Human neural stem cells were modified to express green fluorescent protein and firefly luciferase. Cells were implanted in the fimbria fornix of the hippocampus and viability assessed by non-invasive bioluminescent imaging. Cell survival was assessed using traditional pharmacologic immunosuppression as compared to monoclonal antibodies directed against CD4 and CD40L. This paradigm was also implemented in a transgenic Alzheimer's disease mouse model.

RESULTS

Graft rejection occurs within 7 days in non-immunosuppressed mice and within 14 days in mice on a traditional regimen. The addition of dual monoclonal antibody immunosuppression extends graft survival past 7 weeks (p < .001) on initial studies. We confirm dual monoclonal antibody treatment is superior to either antibody alone (p < .001). Finally, we demonstrate robust xenograft survival at multiple cell doses up to 6 months in both C57BL/6J mice and a transgenic Alzheimer's disease model (p < .001). The dual monoclonal antibody protocol demonstrated no significant adverse effects, as determined by complete blood counts and toxicity screen.

CONCLUSIONS

This study demonstrates an effective immunosuppression protocol for preclinical testing of stem cell therapies. A transition towards antibody-based strategies may be advantageous by enabling stem cell survival in preclinical studies that could inform future clinical trials.