Mechanisms of autophagy-lysosome dysfunction in neurodegenerative diseases.

Autophagy is a lysosome-based degradative process used to recycle obsolete cellular constituents and eliminate damaged organelles and aggregate-prone proteins. Their postmitotic nature and extremely polarized morphologies make neurons particularly vulnerable to disruptions caused by autophagy-lysosomal defects, especially as the brain ages. Consequently, mutations in genes regulating autophagy and lysosomal functions cause a wide range of neurodegenerative diseases. Here, we review the role of autophagy and lysosomes in neurodegenerative diseases such as Alzheimer disease, Parkinson disease and frontotemporal dementia. We also consider the strong impact of cellular ageing on lysosomes and autophagy as a tipping point for the late-age emergence of related neurodegenerative disorders. Many of these diseases have primary defects in autophagy, for example affecting autophagosome formation, and in lysosomal functions, especially pH regulation and calcium homeostasis. We have aimed to provide an integrative framework for understanding the central importance of autophagic-lysosomal function in neuronal health and disease.

Pathophysiologic abnormalities in transgenic mice carrying the Alzheimer disease PSEN1 Δ440 mutation.

Mutations in PSEN1 were first discovered as a cause of Alzheimer's disease (AD) in 1995, yet the mechanism(s) by which the mutations cause disease still remains unknown. The generation of novel mouse models assessing the effects of different mutations could aid in this endeavor. Here we report on transgenic mouse lines made with the Δ440 PSEN1 mutation that causes AD with parkinsonism:- two expressing the un-tagged human protein and two expressing a HA-tagged version. Detailed characterization of these lines showed that Line 305 in particular, which expresses the untagged protein, develops age-dependent memory deficits and pathologic features, many of which are consistent with features found in AD. Key behavioral and physiological alterations found in the novel 305 line included an age-dependent deficit in spontaneous alternations in the Y-maze, a decrease in exploration of the center of an open field box, a decrease in the latency to fall on a rotarod, a reduction in synaptic strength and pair-pulse facilitation by electrophysiology, and profound alterations to cerebral blood flow regulation. The pathologic alterations found in the line included, significant neuronal loss in the hippocampus and cortex, astrogliosis, and changes in several proteins involved in synaptic and mitochondrial function, Ca2+ regulation, and autophagy. Taken together, these findings suggest that the transgenic lines will be useful for the investigation of AD pathogenesis.

De novo design of proteins housing excitonically coupled chlorophyll special pairs.

Natural photosystems couple light harvesting to charge separation using a 'special pair' of chlorophyll molecules that accepts excitation energy from the antenna and initiates an electron-transfer cascade. To investigate the photophysics of special pairs independently of the complexities of native photosynthetic proteins, and as a first step toward creating synthetic photosystems for new energy conversion technologies, we designed C2-symmetric proteins that hold two chlorophyll molecules in closely juxtaposed arrangements. X-ray crystallography confirmed that one designed protein binds two chlorophylls in the same orientation as native special pairs, whereas a second designed protein positions them in a previously unseen geometry. Spectroscopy revealed that the chlorophylls are excitonically coupled, and fluorescence lifetime imaging demonstrated energy transfer. The cryo-electron microscopy structure of a designed 24-chlorophyll octahedral nanocage with a special pair on each edge closely matched the design model. The results suggest that the de novo design of artificial photosynthetic systems is within reach of current computational methods.

RNAi screening comes of age: improved techniques and complementary approaches.

Gene silencing through sequence-specific targeting of mRNAs by RNAi has enabled genome-wide functional screens in cultured cells and in vivo in model organisms. These screens have resulted in the identification of new cellular pathways and potential drug targets. Considerable progress has been made to improve the quality of RNAi screen data through the development of new experimental and bioinformatics approaches. The recent availability of genome-editing strategies, such as the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 system, when combined with RNAi, could lead to further improvements in screen data quality and follow-up experiments, thus promoting our understanding of gene function and gene regulatory networks.

Non-canonical autophagy functions of ATG16L1 in epithelial cells limit lethal infection by influenza A virus.

Influenza A virus (IAV) and SARS-CoV-2 (COVID-19) cause pandemic infections where cytokine storm syndrome and lung inflammation lead to high mortality. Given the high social and economic cost of respiratory viruses, there is an urgent need to understand how the airways defend against virus infection. Here we use mice lacking the WD and linker domains of ATG16L1 to demonstrate that ATG16L1-dependent targeting of LC3 to single-membrane, non-autophagosome compartments - referred to as non-canonical autophagy - protects mice from lethal IAV infection. Mice with systemic loss of non-canonical autophagy are exquisitely sensitive to low-pathogenicity IAV where extensive viral replication throughout the lungs, coupled with cytokine amplification mediated by plasmacytoid dendritic cells, leads to fulminant pneumonia, lung inflammation and high mortality. IAV was controlled within epithelial barriers where non-canonical autophagy reduced IAV fusion with endosomes and activation of interferon signalling. Conditional mouse models and ex vivo analysis showed that protection against IAV infection of lung was independent of phagocytes and other leucocytes. This establishes non-canonical autophagy in airway epithelial cells as a novel innate defence that restricts IAV infection and lethal inflammation at respiratory surfaces.

Rare coding variants in 35 genes associate with circulating lipid levels-A multi-ancestry analysis of 170,000 exomes.

Large-scale gene sequencing studies for complex traits have the potential to identify causal genes with therapeutic implications. We performed gene-based association testing of blood lipid levels with rare (minor allele frequency < 1%) predicted damaging coding variation by using sequence data from >170,000 individuals from multiple ancestries: 97,493 European, 30,025 South Asian, 16,507 African, 16,440 Hispanic/Latino, 10,420 East Asian, and 1,182 Samoan. We identified 35 genes associated with circulating lipid levels; some of these genes have not been previously associated with lipid levels when using rare coding variation from population-based samples. We prioritize 32 genes in array-based genome-wide association study (GWAS) loci based on aggregations of rare coding variants; three (EVI5, SH2B3, and PLIN1) had no prior association of rare coding variants with lipid levels. Most of our associated genes showed evidence of association among multiple ancestries. Finally, we observed an enrichment of gene-based associations for low-density lipoprotein cholesterol drug target genes and for genes closest to GWAS index single-nucleotide polymorphisms (SNPs). Our results demonstrate that gene-based associations can be beneficial for drug target development and provide evidence that the gene closest to the array-based GWAS index SNP is often the functional gene for blood lipid levels.

Lysosomal proteolysis and autophagy require presenilin 1 and are disrupted by Alzheimer-related PS1 mutations.

Macroautophagy is a lysosomal degradative pathway essential for neuron survival. Here, we show that macroautophagy requires the Alzheimer's disease (AD)-related protein presenilin-1 (PS1). In PS1 null blastocysts, neurons from mice hypomorphic for PS1 or conditionally depleted of PS1, substrate proteolysis and autophagosome clearance during macroautophagy are prevented as a result of a selective impairment of autolysosome acidification and cathepsin activation. These deficits are caused by failed PS1-dependent targeting of the v-ATPase V0a1 subunit to lysosomes. N-glycosylation of the V0a1 subunit, essential for its efficient ER-to-lysosome delivery, requires the selective binding of PS1 holoprotein to the unglycosylated subunit and the Sec61alpha/oligosaccharyltransferase complex. PS1 mutations causing early-onset AD produce a similar lysosomal/autophagy phenotype in fibroblasts from AD patients. PS1 is therefore essential for v-ATPase targeting to lysosomes, lysosome acidification, and proteolysis during autophagy. Defective lysosomal proteolysis represents a basis for pathogenic protein accumulations and neuronal cell death in AD and suggests previously unidentified therapeutic targets.

Exome sequencing of 20,791 cases of type 2 diabetes and 24,440 controls.

Protein-coding genetic variants that strongly affect disease risk can yield relevant clues to disease pathogenesis. Here we report exome-sequencing analyses of 20,791 individuals with type 2 diabetes (T2D) and 24,440 non-diabetic control participants from 5 ancestries. We identify gene-level associations of rare variants (with minor allele frequencies of less than 0.5%) in 4 genes at exome-wide significance, including a series of more than 30 SLC30A8 alleles that conveys protection against T2D, and in 12 gene sets, including those corresponding to T2D drug targets (P = 6.1 × 10-3) and candidate genes from knockout mice (P = 5.2 × 10-3). Within our study, the strongest T2D gene-level signals for rare variants explain at most 25% of the heritability of the strongest common single-variant signals, and the gene-level effect sizes of the rare variants that we observed in established T2D drug targets will require 75,000-185,000 sequenced cases to achieve exome-wide significance. We propose a method to interpret these modest rare-variant associations and to incorporate these associations into future target or gene prioritization efforts.

Structural basis for ultrapotent antibody-mediated neutralization of human metapneumovirus.

Human metapneumovirus (hMPV) is a leading cause of morbidity and hospitalization among children worldwide, however, no vaccines or therapeutics are currently available for hMPV disease prevention and treatment. The hMPV fusion (F) protein is the sole target of neutralizing antibodies. To map the immunodominant epitopes on the hMPV F protein, we isolated a panel of human monoclonal antibodies (mAbs), and the mAbs were assessed for binding avidity, neutralization potency, and epitope specificity. We found the majority of the mAbs target diverse epitopes on the hMPV F protein, and we discovered multiple mAb binding approaches for antigenic site III. The most potent mAb, MPV467, which had picomolar potency, was examined in prophylactic and therapeutic mouse challenge studies, and MPV467 limited virus replication in mouse lungs when administered 24 h before or 72 h after viral infection. We determined the structure of MPV467 in complex with the hMPV F protein using cryo-electron microscopy to a resolution of 3.3 Å, which revealed a complex novel prefusion-specific epitope overlapping antigenic sites II and V on a single protomer. Overall, our data reveal insights into the immunodominant antigenic epitopes on the hMPV F protein, identify a mAb therapy for hMPV F disease prevention and treatment, and provide the discovery of a prefusion-specific epitope on the hMPV F protein.

The pandemic preterm paradox: A test of competing explanations.

Epidemiologists have long argued that side effects of the stress response include preterm birth. Research reports that fear of lethal infection stressed pregnant persons at the outset of the COVID-19 pandemic and that "shutdowns" and "social distancing" impeded access to social support and prenatal care. The decline in preterm births in high-income countries, including the United States (US), during the early months of the pandemic therefore poses a paradox for science. Explanations of this "pandemic preterm paradox" remain untested. We apply time-series modeling to data describing 80 monthly conception cohorts begun in the US from July 2013 through February 2020 to determine which of 3 explanations most parsimoniously explains the paradox. We infer that "prior loss," or the argument that an increase in spontaneous abortions and stillbirths depleted the population of fetuses at risk of preterm birth, best explains data currently available. We describe the implications of these results for public health practice.

Advances and counterpoints in type 2 diabetes. What is ready for translation into real-world practice, ahead of the guidelines.

This review seeks to address major gaps and delays between our rapidly evolving body of knowledge on type 2 diabetes and its translation into real-world practice. Through updated and improved best practices informed by recent evidence and described herein, we stand to better attain A1c targets, help preserve beta cell integrity and moderate glycemic variability, minimize treatment-emergent hypoglycemia, circumvent prescribing to "treatment failure," and prevent long-term complications. The first topic addressed in this review concerns updates in the 2023 and 2024 diabetes treatment guidelines for which further elaboration can help facilitate integration into routine care. The second concerns advances in diabetes research that have not yet found their way into guidelines, though they are endorsed by strong evidence and are ready for real-world use in appropriate patients. The final theme addresses lingering misconceptions about the underpinnings of type 2 diabetes-fundamental fallacies that continue to be asserted in the textbooks and continuing medical education upon which physicians build their approaches. A corrected and up-to-date understanding of the disease state is essential for practitioners to both conceptually and translationally manage initial onset through late-stage type 2 diabetes.

Rationale and design of the early valve replacement in severe asymptomatic aortic stenosis trial.

BACKGROUND: Aortic valve replacement in asymptomatic severe aortic stenosis is controversial. The Early valve replacement in severe ASYmptomatic Aortic Stenosis (EASY-AS) trial aims to determine whether early aortic valve replacement improves clinical outcomes, quality of life and cost-effectiveness compared to a guideline recommended strategy of 'watchful waiting'. METHODS: In a pragmatic international, open parallel group randomized controlled trial (NCT04204915), 2844 patients with severe aortic stenosis will be randomized 1:1 to either a strategy of early (surgical or transcatheter) aortic valve replacement or aortic valve replacement only if symptoms or impaired left ventricular function develop, or other cardiac surgery becomes nessessary. Exclusion criteria include other severe valvular disease, planned cardiac surgery, ejection fraction <50%, previous aortic valve replacement or life expectancy <2 years. The primary outcome is a composite of cardiovascular mortality or heart failure hospitalization. The primary analysis will be undertaken when 663 primary events have accrued, providing 90% power to detect a reduction in the primary endpoint from 27.7% to 21.6% (hazard ratio 0.75). Secondary endpoints include disability-free survival, days alive and out of hospital, major adverse cardiovascular events and quality of life. RESULTS: Recruitment commenced in March 2020 and is open in the UK, Australia, New Zealand, and Serbia. Feasibility requirements were met in July 2022, and the main phase opened in October 2022, with additional international centers in set-up. CONCLUSIONS: The EASY-AS trial will establish whether a strategy of early aortic valve replacement in asymptomatic patients with severe aortic stenosis reduces cardiovascular mortality or heart failure hospitalization and improves other important outcomes.

Autophagy-lysosomal-associated neuronal death in neurodegenerative disease.

Autophagy, the major lysosomal pathway for degrading damaged or obsolete constituents, protects neurons by eliminating toxic organelles and peptides, restoring nutrient and energy homeostasis, and inhibiting apoptosis. These functions are especially vital in neurons, which are postmitotic and must survive for many decades while confronting mounting challenges of cell aging. Autophagy failure, especially related to the declining lysosomal ("phagy") functions, heightens the neuron's vulnerability to genetic and environmental factors underlying Alzheimer's disease (AD) and other late-age onset neurodegenerative diseases. Components of the global autophagy-lysosomal pathway and the closely integrated endolysosomal system are increasingly implicated as primary targets of these disorders. In AD, an imbalance between heightened autophagy induction and diminished lysosomal function in highly vulnerable pyramidal neuron populations yields an intracellular lysosomal build-up of undegraded substrates, including APP-ßCTF, an inhibitor of lysosomal acidification, and membrane-damaging Aß peptide. In the most compromised of these neurons, ß-amyloid accumulates intraneuronally in plaque-like aggregates that become extracellular senile plaques when these neurons die, reflecting an "inside-out" origin of amyloid plaques seen in human AD brain and in mouse models of AD pathology. In this review, the author describes the importance of lysosomal-dependent neuronal cell death in AD associated with uniquely extreme autophagy pathology (PANTHOS) which is described as triggered by lysosomal membrane permeability during the earliest "intraneuronal" stage of AD. Effectors of other cell death cascades, notably calcium-activated calpains and protein kinases, contribute to lysosomal injury that induces leakage of cathepsins and activation of additional death cascades. Subsequent events in AD, such as microglial invasion and neuroinflammation, induce further cytotoxicity. In major neurodegenerative disease models, neuronal death and ensuing neuropathologies are substantially remediable by reversing underlying primary lysosomal deficits, thus implicating lysosomal failure and autophagy dysfunction as primary triggers of lysosomal-dependent cell death and AD pathogenesis and as promising therapeutic targets.

A systemic cell cycle block impacts stage-specific histone modification profiles during Xenopus embryogenesis.

Forming an embryo from a zygote poses an apparent conflict for epigenetic regulation. On the one hand, the de novo induction of cell fate identities requires the establishment and subsequent maintenance of epigenetic information to harness developmental gene expression. On the other hand, the embryo depends on cell proliferation, and every round of DNA replication dilutes preexisting histone modifications by incorporation of new unmodified histones into chromatin. Here, we investigated the possible relationship between the propagation of epigenetic information and the developmental cell proliferation during Xenopus embryogenesis. We systemically inhibited cell proliferation during the G1/S transition in gastrula embryos and followed their development until the tadpole stage. Comparing wild-type and cell cycle-arrested embryos, we show that the inhibition of cell proliferation is principally compatible with embryo survival and cellular differentiation. In parallel, we quantified by mass spectrometry the abundance of a large set of histone modification states, which reflects the developmental maturation of the embryonic epigenome. The arrested embryos developed abnormal stage-specific histone modification profiles (HMPs), in which transcriptionally repressive histone marks were overrepresented. Embryos released from the cell cycle block during neurulation reverted toward normality on morphological, molecular, and epigenetic levels. These results suggest that the cell cycle block by HUA alters stage-specific HMPs. We propose that this influence is strong enough to control developmental decisions, specifically in cell populations that switch between resting and proliferating states such as stem cells.

Swelling of Thin Graphene Oxide Film in Water Vapor Studied by In Situ Spectroscopic Ellipsometry.

Graphene oxide (GO) is obtained by the chemical treatment of graphene sheets, resulting in decoration with oxygen-containing functional groups. In the work presented here, we examined marked changes that occur in a thin film of parallel aligned GO sheets when exposed to water vapor at various pressures. It was found that exceptionally fast and substantial water uptake and release occur that is accompanied by major changes in GO interlayer spacing. These characteristics were obtained in situ with spectroscopic ellipsometry. At 99% relative humidity (RH) and 25 °C, the interlayer spacing became 1.41 nm, which recovers to ∼0.8 nm within 30 s when exposed to 10% RH. Besides layer thickness values, uniaxial optical constants for the GO vs RH were derived from the ellipsometry data. Molar refraction theory was applied that indicated monolayer water formation at ∼91% RH at 25 °C upon water adsorption. Our findings contribute to the understanding of the interaction between GO and its environment. The very outspoken effect of external water vapor pressure on GO water content, interlayer spacing, and optical properties can be utilized in sensing and separation devices, subnanometer positioning, chemical switches, and environmentally aware materials.

The impact of increased hepatic glucose production caused by empagliflozin on plasma glucose concentration in individuals with type 2 diabetes and nondiabetic individuals.

AIM: To examine the impact of increased hepatic glucose production (HGP) on the decrease in plasma glucose concentration caused by empagliflozin in individuals living with diabetes and in nondiabetic individuals. METHODS: A total of 36 individuals living with diabetes and 34 nondiabetic individuals were randomized to receive, in double-blind fashion, empagliflozin or matching placebo in a 2:1 treatment ratio. Following an overnight fast, HGP was measured with 3-3 H-glucose infusion before, at the start of, and 3 months after therapy with empagliflozin. RESULTS: On Day 1 of empagliflozin administration, the increase in urinary glucose excretion (UGE) in individuals with normal glucose tolerance was smaller than in those with impaired glucose tolerance and those living with diabetes, and was accompanied by an increase in HGP in all three groups. The amount of glucose returned to the systemic circulation as a result of the increase in HGP was smaller than that excreted by the kidney during the first 3 h after empagliflozin administration, resulting in a decrease in fasting plasma glucose (FPG) concentration. After 3 h, the increase in HGP was in excess of UGE, leading to a small increase in plasma glucose concentration, which reached a new steady state. After 12 weeks, the amount of glucose returned to the circulation due to the empagliflozin-induced increase in HGP was comparable with that excreted by the kidney in all three groups. CONCLUSION: The balance between UGE and increase in HGP immediately after sodium-glucose cotransporter-2 (SGLT2) inhibition determined the magnitude of decrease in FPG and the new steady state which was achieved. After 12 weeks, the increase in HGP caused by empagliflozin closely matched the amount of glucose excreted by the kidneys; thus, FPG level remained stable despite the continuous urinary excretion of glucose caused by SGLT2 inhibition.

Fixed-node diffusion Monte Carlo shows promise for modeling reaction thermochemistry of hydrocarbon-based radicals.

Reliable thermodynamic and kinetic properties of free radical polymerization reactions are essential for synthesizing both primary polymeric materials and specialty polymers. The computational generation of these data from quantum chemistry requires a time-efficient method capable of capturing the essential physics. One such method, fixed-node diffusion Monte Carlo (FN-DMC) (using single Slater-Jastrow trial wavefunctions), has demonstrated the capability to recover 90%-95% of missing dynamic correlation energy for typical systems. In this study, methyl radical addition to ethylene serves as a simple model to test FN-DMC's ability to calculate enthalpies of reaction and activation energies with different time steps, antisymmetric trial wavefunctions, basis set sizes, and effective core potentials. The FN-DMC computational protocol thus defined for methyl radical addition to ethylene is subsequently benchmarked against Weizmann-1 and experimental reaction enthalpies from Lin et al.'s test set of 21 radical addition and 28 hydrogen abstraction enthalpies. Our findings reveal that FN-DMC consistently generates reaction enthalpies with chemical accuracy, exhibiting mean absolute deviation of 3.5(7) and 1.4(8) kJ/mol from the Weizmann-1 reference for radical addition and hydrogen abstraction reactions, respectively. Given its favorable computational scaling and high degree of parallelizability, we, therefore, recommend more comprehensive testing of FN-DMC with effective core potentials to address more extensive and intricate polymerization reactions and reactions with other radicals.

Dual oxidase 1 promotes antiviral innate immunity.

Dual oxidase 1 (DUOX1) is an NADPH oxidase that is highly expre-ssed in respiratory epithelial cells and produces H2O2 in the airway lumen. While a line of prior in vitro observations suggested that DUOX1 works in partnership with an airway peroxidase, lactoperoxidase (LPO), to produce antimicrobial hypothiocyanite (OSCN-) in the airways, the in vivo role of DUOX1 in mammalian organisms has remained unproven to date. Here, we show that Duox1 promotes antiviral innate immunity in vivo. Upon influenza airway challenge, Duox1-/- mice have enhanced mortality, morbidity, and impaired lung viral clearance. Duox1 increases the airway levels of several cytokines (IL-1ß, IL-2, CCL1, CCL3, CCL11, CCL19, CCL20, CCL27, CXCL5, and CXCL11), contributes to innate immune cell recruitment, and affects epithelial apoptosis in the airways. In primary human tracheobronchial epithelial cells, OSCN- is generated by LPO using DUOX1-derived H2O2 and inactivates several influenza strains in vitro. We also show that OSCN- diminishes influenza replication and viral RNA synthesis in infected host cells that is inhibited by the H2O2 scavenger catalase. Binding of the influenza virus to host cells and viral entry are both reduced by OSCN- in an H2O2-dependent manner in vitro. OSCN- does not affect the neuraminidase activity or morphology of the influenza virus. Overall, this antiviral function of Duox1 identifies an in vivo role of this gene, defines the steps in the infection cycle targeted by OSCN-, and proposes that boosting this mechanism in vivo can have therapeutic potential in treating viral infections.

Unexplained Residual Risk In Type 2 Diabetes: How Big Is The Problem?

PURPOSE OF REVIEW: What is new? Cardiovascular disease (CVD) is the leading cause of mortality in type 2 diabetes (T2D) individuals. Of the major risk factors for CVD, less than 10% of T2D people meet the American Diabetes Association/American Heart Association recommended goals of therapy. The present review examines how much of the absolute cardiovascular (CV) risk in type 2 diabetes patients can be explained by major CV intervention trials. RECENT FINDINGS: Multiple long-term cardiovascular (CV) intervention trials have examined the effect of specific target-directed therapies on the MACE endpoint. Only one prospective study, STENO-2, has employed a multifactorial intervention comparing intensified versus conventional treatment of modifiable risk factors in T2D patients, and demonstrated a 20% absolute CV risk reduction. If the absolute CV risk reduction in these trials is added to that in the only prospective multifactorial intervention trial (STENO-2), the unexplained CV risk is 44.1%. What are the clinical implications? Potential explanations for the unaccounted-for reduction in absolute CV risk in type 2 diabetes (T2D) patients are discussed. HYPOTHESIS: failure to take into account synergistic interactions between major cardiovascular risk factors is responsible for the unexplained CV risk in T2D patients. Simultaneous treatment of all major CV risk factors to recommended AHA/ADA guideline goals is required to achieve the maximum reduction in CV risk.

Understanding resident wellness: A path analysis of the clinical learning environment at three institutions.

PURPOSE: The clinical learning environment (CLE) affects resident physician well-being. This study assessed how aspects of the learning environment affected the level of resident job stress and burnout. MATERIALS AND METHODS: Three institutions surveyed residents assessing aspects of the CLE and well-being via anonymous survey in fall of 2020 during COVID. Psychological safety (PS) and perceived organizational support (POS) were used to capture the CLE, and the Mini-Z Scale was used to assess resident job stress and burnout. A total of 2,196 residents received a survey link; 889 responded (40% response rate). Path analysis explored both direct and indirect relationships between PS, POS, resident stress, and resident burnout. RESULTS: Both POS and PS had significant negative relationships with experiencing a great deal of job stress; the relationship between PS and stress was noticeably stronger than POS and stress (POS: B= -0.12, p=.025; PS: B= -0.37, p<.001). The relationship between stress and residents' level of burnout was also significant (B = 0.38, p<.001). The overall model explained 25% of the variance in resident burnout. CONCLUSIONS: Organizational support and psychological safety of the learning environment is associated with resident burnout. It is important for educational leaders to recognize and mitigate these factors.