Characterizing molecular and synaptic signatures in mouse models of late-onset Alzheimer's disease independent of amyloid and tau pathology.

INTRODUCTION: MODEL-AD (Model Organism Development and Evaluation for Late-Onset Alzheimer's Disease) is creating and distributing novel mouse models with humanized, clinically relevant genetic risk factors to capture the trajectory and progression of late-onset Alzheimer's disease (LOAD) more accurately. METHODS: We created the LOAD2 model by combining apolipoprotein E4 (APOE4), Trem2*R47H, and humanized amyloid-beta (Aß). Mice were subjected to a control diet or a high-fat/high-sugar diet (LOAD2+HFD). We assessed disease-relevant outcome measures in plasma and brain including neuroinflammation, Aß, neurodegeneration, neuroimaging, and multi-omics. RESULTS: By 18 months, LOAD2+HFD mice exhibited sex-specific neuron loss, elevated insoluble brain Aß42, increased plasma neurofilament light chain (NfL), and altered gene/protein expression related to lipid metabolism and synaptic function. Imaging showed reductions in brain volume and neurovascular uncoupling. Deficits in acquiring touchscreen-based cognitive tasks were observed. DISCUSSION: The comprehensive characterization of LOAD2+HFD mice reveals that this model is important for preclinical studies seeking to understand disease trajectory and progression of LOAD prior to or independent of amyloid plaques and tau tangles. HIGHLIGHTS: By 18 months, unlike control mice (e.g., LOAD2 mice fed a control diet, CD), LOAD2+HFD mice presented subtle but significant loss of neurons in the cortex, elevated levels of insoluble Ab42 in the brain, and increased plasma neurofilament light chain (NfL). Transcriptomics and proteomics showed changes in gene/proteins relating to a variety of disease-relevant processes including lipid metabolism and synaptic function. In vivo imaging revealed an age-dependent reduction in brain region volume (MRI) and neurovascular uncoupling (PET/CT). LOAD2+HFD mice also demonstrated deficits in acquisition of touchscreen-based cognitive tasks.

Increasing Early Skin-to-Skin in Extremely Low Birth Weight Infants.

BACKGROUND: Early skin-to-skin care (SSC) has been shown to improve outcomes after preterm birth, including improved clinical stability and establishment of breastfeeding. Recent evidence suggests the most unstable infants get the most benefit, yet these infants are not consistently offered opportunities for SSC because of safety concerns and discomfort of the care team. PURPOSE: To identify barriers and implement a multidimensional approach to increase SSC within the first 72 hours of life among infants born less than 28 weeks' gestation and less than 1,000 g in a Level IV university-based regional intensive care nursery. METHODS: Using Institute of Healthcare Improvement quality improvement methodology, a multidisciplinary team identified barriers to SSC and developed targeted interventions, including a unit-specific protocol; widespread parent, staff, and provider education; and an infant readiness checklist. The primary outcome was the rate of SSC within 72 hours. The balancing measure was the rate of severe intraventricular hemorrhage (IVH). Data were collected from monthly chart review and analyzed with statistical process control charts. The aim was to increase SSC within 72 hours of birth from 7 percent to greater than 80 percent within 12 months for infants born less than 28 weeks' gestation or less than 1,000 g. RESULTS: Between June 2017 and December 2019, there were 52 extremely preterm infants included in the project (15 preintervention and 37 postintervention). The rate of SSC within the first 72 hours increased from 7 to 84 percent. There has been no increase in any or severe IVH during the project period despite the increased rate of SSC. IMPLICATIONS FOR PRACTICE: Implementation of multidimensional, multidisciplinary interventions for reducing barriers to early SSC in extremely preterm infants resulted in rapid adoption of SSC in the first 72 hours of life without increasing severe IVH in this high-risk population.

Degradation of Transcriptional Repressor ATF4 during Long-Term Synaptic Plasticity.

Maintenance of long-term synaptic plasticity requires gene expression mediated by cAMP-responsive element binding protein (CREB). Gene expression driven by CREB can commence only if the inhibition by a transcriptional repressor activating transcription factor 4 (ATF4; also known as CREB2) is relieved. Previous research showed that the removal of ATF4 occurs through ubiquitin-proteasome-mediated proteolysis. Using chemically induced hippocampal long-term potentiation (cLTP) as a model system, we investigate the mechanisms that control ATF4 degradation. We observed that ATF4 phosphorylated at serine-219 increases upon induction of cLTP and decreases about 30 min thereafter. Proteasome inhibitor ß-lactone prevents the decrease in ATF4. We found that the phosphorylation of ATF4 is mediated by cAMP-dependent protein kinase. Our initial experiments towards the identification of the ligase that mediates ubiquitination of ATF4 revealed a possible role for ß-transducin repeat containing protein (ß-TrCP). Regulation of ATF4 degradation is likely to be a mechanism for determining the threshold for gene expression underlying maintenance of long-term synaptic plasticity and by extension, long-term memory.

Proteasome modulates positive and negative translational regulators in long-term synaptic plasticity.

Proteolysis by the ubiquitin-proteasome pathway appears to have a complex role in synaptic plasticity, but its various functions remain to be elucidated. Using late phase long-term potentiation (L-LTP) in the hippocampus of the mouse as a model for long-term synaptic plasticity, we previously showed that inhibition of the proteasome enhances induction but blocks maintenance of L-LTP. In this study, we investigated the possible mechanisms by which proteasome inhibition has opposite effects on L-LTP induction and maintenance. Our results show that inhibiting phosphatidyl inositol-3 kinase or blocking the interaction between eukaryotic initiation factors 4E (eIF4E) and 4G (eIF4G) reduces the enhancement of L-LTP induction brought about by proteasome inhibition suggesting interplay between proteolysis and the signaling pathway mediated by mammalian target of rapamycin (mTOR). Also, proteasome inhibition leads to accumulation of translational activators in the mTOR pathway such as eIF4E and eukaryotic elongation factor 1A (eEF1A) early during L-LTP causing increased induction. Furthermore, inhibition of the proteasome causes a buildup of translational repressors, such as polyadenylate-binding protein interacting protein 2 (Paip2) and eukaryotic initiation factor 4E-binding protein 2 (4E-BP2), during late stages of L-LTP contributing to the blockade of L-LTP maintenance. Thus, the proteasome plays a critical role in regulating protein synthesis during L-LTP by tightly controlling translation. Our results provide novel mechanistic insights into the interplay between protein degradation and protein synthesis in long-term synaptic plasticity.

Characterizing Molecular and Synaptic Signatures in mouse models of Late-Onset Alzheimer's Disease Independent of Amyloid and Tau Pathology.

INTRODUCTION: MODEL-AD is creating and distributing novel mouse models with humanized, clinically relevant genetic risk factors to more accurately mimic LOAD than commonly used transgenic models. METHODS: We created the LOAD2 model by combining APOE4, Trem2*R47H, and humanized amyloid-beta. Mice aged up to 24 months were subjected to either a control diet or a high-fat/high-sugar diet (LOAD2+HFD) from two months of age. We assessed disease-relevant outcomes, including in vivo imaging, biomarkers, multi-omics, neuropathology, and behavior. RESULTS: By 18 months, LOAD2+HFD mice exhibited cortical neuron loss, elevated insoluble brain Aß42, increased plasma NfL, and altered gene/protein expression related to lipid metabolism and synaptic function. In vivo imaging showed age-dependent reductions in brain region volume and neurovascular uncoupling. LOAD2+HFD mice also displayed deficits in acquiring touchscreen-based cognitive tasks. DISCUSSION: Collectively the comprehensive characterization of LOAD2+HFD mice reveal this model as important for preclinical studies that target features of LOAD independent of amyloid and tau.

Reduction of Severe Intraventricular Hemorrhage in Preterm Infants: A Quality Improvement Project.

OBJECTIVES: The aim of this quality improvement project was to reduce the rate of severe intraventricular hemorrhage (sIVH) by 50% within 3 years for extremely preterm infants born at a children's teaching hospital. METHODS: A multidisciplinary team developed key drivers for the development of intraventricular hemorrhage in preterm infants. Targeted interventions included the development of potentially better practice guidelines, promoting early noninvasive ventilation, consistent use of rescue antenatal betamethasone, and risk-based indomethacin prophylaxis. The outcome measure was the rate of sIVH. Process measures included the rate of intubation within 24 hours and receipt of rescue betamethasone and risk-based indomethacin prophylaxis. Common markers of morbidity were balancing measures. Data were collected from a quarterly chart review and analyzed with statistical process control charts. The preintervention period was from January 2012 to March 2016, implementation period was from April 2016 to December 2018, and sustainment period was through June 2020. RESULTS: During the study period, there were 268 inborn neonates born at <28 weeks' gestation or <1000 g (127 preintervention and 141 postintervention). The rate of sIVH decreased from 14% to 1.2%, with sustained improvement over 2 and a half years. Mortality also decreased by 50% during the same time period. This was associated with adherence to process measures and no change in balancing measures. CONCLUSIONS: A multipronged quality improvement approach to intraventricular hemorrhage prevention, including evidence-based practice guidelines, consistent receipt of rescue betamethasone and indomethacin prophylaxis, and decreasing early intubation was associated with a sustained reduction in sIVH in extremely preterm infants.

Proteasome inhibition augments new protein accumulation early in long-term synaptic plasticity and rescues adverse Aß effects on protein synthesis.

Protein degradation plays a critical role in synaptic plasticity, but the molecular mechanisms are not well understood. Previously we showed that proteasome inhibition enhances the early induction part of long-term synaptic plasticity for which protein synthesis is essential. In this study, we tested the effect of proteasome inhibition on protein synthesis using a chemically induced long-lasting synaptic plasticity (cLTP) in the murine hippocampus as a model system. Our metabolic labeling experiments showed that cLTP induction increases protein synthesis and proteasome inhibition enhances the amount of newly synthesized proteins. We then found that amyloid beta (Aß), a peptide contributing to Alzheimer's pathology and impairment of synaptic plasticity, blocks protein synthesis increased by cLTP. This blockade can be reversed by prior proteasome inhibition. Thus, our work reveals interactions between protein synthesis and protein degradation and suggests a possible way to exploit protein degradation to rescue adverse Aß effects on long-term synaptic plasticity.

Local ubiquitin-proteasome-mediated proteolysis and long-term synaptic plasticity.

The ubiquitin-proteasome pathway (UPP) of protein degradation has many roles in synaptic plasticity that underlies memory. Work on both invertebrate and vertebrate model systems has shown that the UPP regulates numerous substrates critical for synaptic plasticity. Initial research took a global view of ubiquitin-protein degradation in neurons. Subsequently, the idea of local protein degradation was proposed a decade ago. In this review, we focus on the functions of the UPP in long-term synaptic plasticity and discuss the accumulated evidence in support of the idea that the components of the UPP often have disparate local roles in different neuronal compartments rather than a single cell-wide function.

Muscarinic receptor/G-protein coupling is reduced in the dorsomedial striatum of cognitively impaired aged rats.

Behavioral flexibility, the ability to modify responses due to changing task demands, is detrimentally affected by aging with a shift towards increased cognitive rigidity. The neurobiological basis of this cognitive deficit is not clear although striatal cholinergic neurotransmission has been implicated. To investigate the possible association between striatal acetylcholine signaling with age-related changes in behavioral flexibility, young, middle-aged, and aged F344 X Brown Norway F1 rats were assessed using an attentional set-shifting task that includes two tests of behavioral flexibility: reversal learning and an extra-dimensional shift. Rats were also assessed in the Morris water maze to compare potential fronto-striatal-dependent deficits with hippocampal-dependent deficits. Behaviorally characterized rats were then assessed for acetylcholine muscarinic signaling within the striatum using oxotremorine-M-stimulated [(35)S]GTPγS binding and [(3)H]AFDX-384 receptor binding autoradiography. The results showed that by old age, cognitive deficits were pronounced across cognitive domains, suggesting deterioration of both hippocampal and fronto-striatal regions. A significant decline in oxotremorine-M-stimulated [(35)S]GTPγS binding was limited to the dorsomedial striatum of aged rats when compared to young and middle-aged rats. There was no effect of age on striatal [(3)H]AFDX-384 receptor binding. These results suggest that a decrease in M2/M4 muscarinic receptor coupling is involved in the age-associated decline in behavioral flexibility.