Mitochondrial Dysfunction in Huntington's Disease; Interplay Between HSF1, p53 and PGC-1α Transcription Factors

Huntington's disease (HD) is a neurodegenerative disease caused by an expanded CAG repeat in the huntingtin (HTT) gene, causing the protein to misfold and aggregate. HD progression is characterized by motor impairment and cognitive decline associated with the preferential loss of striatal medium spiny neurons (MSNs). The mechanisms that determine increased susceptibility of MSNs to mutant HTT (mHTT) are not fully understood, although there is abundant evidence demonstrating the importance of mHTT mediated mitochondrial dysfunction in MSNs death. Two main transcription factors, p53 and peroxisome proliferator co-activator PGC-1α, have been widely studied in HD for their roles in regulating mitochondrial function and apoptosis. The action of these two proteins seems to be interconnected. However, it is still open to discussion whether p53 and PGC-1α dependent responses directly influence each other or if they are connected via a third mechanism. Recently, the stress responsive transcription factor HSF1, known for its role in protein homeostasis, has been implicated in mitochondrial function and in the regulation of PGC-1α and p53 levels in different contexts. Based on previous reports and our own research, we discuss in this review the potential role of HSF1 in mediating mitochondrial dysfunction in HD and propose a unifying mechanism that integrates the responses mediated by p53 and PGC-1α in HD via HSF1.

Heat Shock Factor 1 Directly Regulates Postsynaptic Scaffolding PSD-95 in Aging and Huntington's Disease and Influences Striatal Synaptic Density

PSD-95 (Dlg4) is an ionotropic glutamate receptor scaffolding protein essential in synapse stability and neurotransmission. PSD-95 levels are reduced during aging and in neurodegenerative diseases like Huntington's disease (HD), and it is believed to contribute to synaptic dysfunction and behavioral deficits. However, the mechanism responsible for PSD-95 dysregulation under these conditions is unknown. The Heat Shock transcription Factor 1 (HSF1), canonically known for its role in protein homeostasis, is also depleted in both aging and HD. Synaptic protein levels, including PSD-95, are influenced by alterations in HSF1 levels and activity, but the direct regulatory relationship between PSD-95 and HSF1 has yet to be determined. Here, we showed that HSF1 chronic or acute reduction in cell lines and mice decreased PSD-95 expression. Furthermore, Hsf1(+/-) mice had reduced PSD-95 synaptic puncta that paralleled a loss in thalamo-striatal excitatory synapses, an important circuit disrupted early in HD. We demonstrated that HSF1 binds to regulatory elements present in the PSD-95 gene and directly regulates PSD-95 expression. HSF1 DNA-binding on the PSD-95 gene was disrupted in an age-dependent manner in WT mice and worsened in HD cells and mice, leading to reduced PSD-95 levels. These results demonstrate a direct role of HSF1 in synaptic gene regulation that has important implications in synapse maintenance in basal and pathological conditions.

Tumor suppressor p53 regulates heat shock factor 1 protein degradation in Huntington's disease

p53 and HSF1 are two major transcription factors involved in cell proliferation and apoptosis, whose dysregulation contributes to cancer and neurodegeneration. Contrary to most cancers, p53 is increased in Huntington's disease (HD) and other neurodegenerative diseases, while HSF1 is decreased. p53 and HSF1 reciprocal regulation has been shown in different contexts, but their connection in neurodegeneration remains understudied. Using cellular and animal models of HD, we show that mutant HTT stabilized p53 by abrogating the interaction between p53 and E3 ligase MDM2. Stabilized p53 promotes protein kinase CK2 alpha prime and E3 ligase FBXW7 transcription, both of which are responsible for HSF1 degradation. Consequently, p53 deletion in striatal neurons of zQ175 HD mice restores HSF1 abundance and decrease HTT aggregation and striatal pathology. Our work shows the mechanism connecting p53 stabilization with HSF1 degradation and pathophysiology in HD and sheds light on the broader molecular differences and commonalities between cancer and neurodegeneration.

0583 Tolerance and feasibility of daytime bright light in medical intensive care unit patients

Introduction

Sleep and circadian disruption in critical illness are associated with poor outcomes. Normal circadian entrainment requires bright light exposure during the day and dim or no light during the night. Disruption of this diurnal light pattern can cause circadian abnormalities. To leverage this highly influential circadian entrainment cue, our study investigates the tolerance and feasibility of a daytime bright light (DBL) intervention in the medical ICU (MICU). We hypothesize that DBL is tolerable and has high fidelity and sustainability (i.e., feasibility).

Methods

Here we present the findings of a pilot randomized control trial of DBL in MICU patients. Patients were randomized to receive light for either 4 hours, 8 hours, or no light (usual care). For DBL groups, the light was turned on at 09:00 daily for 4 consecutive days. Metrics of tolerability (percentage of days patient agreed to light), fidelity (percentage of intended hours light was delivered), and sustainability (percentage of days light delivered out of days patients allowed light) were collected.

Results

Sixteen patients were enrolled; 5 were assigned to 8 hours of DBL, 9 were assigned to 4 hours of DBL, and 2 were assigned to usual care. Mean (standard deviation) patient age was 73 (10) and mean severity of illness, as determined by Acute Physiology and Chronic Health Evaluation II score, was 21(5). Patients who received 4 hours of DBL averaged 69% tolerability, 55% fidelity, and 94% sustainability. Patients who received 8 hours of DBL averaged 70% tolerability, 57% fidelity, and 90% sustainability. Further analysis of light delivery data showed that the 8-hour group was subject to a higher number of requests to delay light start or end light early and more care related breaks versus the 4-hour group.

Conclusion

Our study demonstrates the feasibility of a DBL intervention for MICU patients. While fidelity was lower than expected, the findings support that DBL is tolerable and sustainable in critically-ill patients. These findings have influenced the design of our ongoing randomized control trial further evaluating the impact of daytime bright light on circadian phase in critical illness.

Support (If Any)

This work was supported by the NHLBI (K23 HL138229), the Academy of Sleep Medicine Foundation, and the Fund to Retain Clinical Scientists at Yale sponsored by the Doris Duke Charitable Foundation award #2015216 and the Yale Center for Clinical Investigation.

Early goal enteral nutrition associated with decreased in-hospital death in mechanically ventilated critically ill adults: a retrospective cohort study

INTRODUCTION

Early enteral nutrition (EN) in critically ill adult patients is thought to improve mortality and morbidity; expert guidelines recommend early initiation of EN in critically ill adults. However, the ideal schedule and dose of EN remain understudied.

STUDY OBJECTIVE

Our objective was to evaluate the relationship between achieving 70% of recommended EN within 2 days of intubation ('early goal EN') and clinical outcomes in mechanically ventilated medically critically ill adults. We hypothesised that early goal EN would be associated with reduced in-hospital death.

METHODS

We conducted a retrospective cohort study of mechanically ventilated adult patients admitted to our medical intensive care unit during 2013-2019. We assessed the proportion of recommended total EN provided to the patient each day following intubation until extubation, death or 7 days whichever was shortest. Patients who received 70% or more of their recommended total daily EN within 2 days of intubation (ie, 'baseline period') were considered to have achieved 'early goal EN'; these patients were compared with patients who did not ('low EN'). The primary outcome was in-hospital death; secondary outcomes were successful extubation and discharge alive.

RESULTS

938 patients met eligibility criteria and survived the baseline period. During the 7-day postintubation period, 64% of all patients reached 70% of recommended daily calories; 33% of patients achieved early goal EN. In unadjusted and adjusted models, early goal EN versus low EN was associated with a lower incidence of in-hospital death (subdistribution HR (SHR) unadjusted=0.63, p=0.0003, SHR adjusted=0.73, p=0.02). Early goal EN was also associated with a higher incidence of successful extubation (SHR unadjusted=1.41, p<0.00001, SHR adjusted=1.27, p=0.002) and discharge alive (SHR unadjusted=1.54, p<0.00001, SHR adjusted=1.24, p=0.02).

CONCLUSIONS

Early goal EN was associated with significant improvement in clinical metrics of decreased in-hospital death, increased extubation and increased hospital discharge alive.