Biology subjects

Wiseman, L.

Publications and source records attributed to Wiseman, L..

27 records · Page 2Linked to original sources

bioRxiv2022

ATF6 Activation Reduces Amyloidogenic Transthyretin Secretion Through Increased Interactions with Endoplasmic Reticulum Proteostasis Factors

The extracellular aggregation of destabilized transthyretin (TTR) variants is implicated in the onset and pathogenesis of familial TTR-related amyloid diseases. One strategy to reduce toxic, extracellular aggregation of TTR is to decrease the population of aggregation-prone protein secreted from mammalian cells. Stress-independent activation of the unfolded protein response (UPR)-associated transcription factor ATF6 preferentially decreases secretion and subsequent aggregation of destabilized, aggregation-prone TTR variants. However, the mechanism of this reduced secretion was previously undefined. Here, we implement a mass spectrometry-based interactomics approach to identify endoplasmic reticulum (ER) proteostasis factors involved in ATF6-dependent reductions of destabilized TTR secretion. We show that ATF6 activation reduces amyloidogenic TTR secretion and subsequent aggregation through a mechanism involving ER retention that is mediated by increased interactions with ATF6-regulated ER proteostasis factors including BiP and PDIA4. Intriguingly, the PDIA4-dependent retention of TTR is independent of both the single TTR cysteine residue and the redox activity of PDIA4, indicating that PDIA4 retains destabilized TTR in the ER through a redox-independent chaperoning activity. Our results define a mechanistic basis to explain the ATF6 activation-dependent reduction of destabilized, amyloidogenic TTR secretion that could be therapeutically accessed to improve treatments of TTR-related amyloid diseases.

cell biology↗

bioRxiv2022

Circadian disruption enhances HSF1 signaling and tumorigenesis in Kras-driven lung cancer

Disrupted circadian rhythmicity is a prominent feature of modern society and has been designated as a probable carcinogen by the World Health Organization. However, the biological mechanisms that connect circadian disruption and cancer risk remain largely undefined. We demonstrate that exposure to chronic circadian disruption (chronic jetlag, CJL) increases tumor burden in a mouse model of KRAS-driven lung cancer. Molecular characterization of tumors and tumor-bearing lung tissues revealed that CJL enhances the expression of heat shock factor 1 (HSF1) target genes. Consistently, exposure to CJL disrupted the highly rhythmic nuclear trafficking of HSF1 in the lung, resulting in an enhanced accumulation of HSF1 in the nucleus. HSF1 has been shown to promote tumorigenesis in other systems, and we find that pharmacological inhibition of HSF1 reduces the growth of KRAS-mutant human lung cancer cells. These findings implicate HSF1 as a molecular link between circadian disruption and enhanced tumorigenesis.

cell biology↗

bioRxiv2021

Metabolically Activated Proteostasis Regulators Protect Against Glutamate Toxicity by Activating NRF2

The extracellular accumulation of glutamate is a pathologic hallmark of numerous neurodegenerative diseases including ischemic stroke and Alzheimers disease. At high extracellular concentrations, glutamate causes neuronal damage by promoting oxidative stress which can lead to cellular death. This has led to significant interest in developing pharmacologic approaches to mitigate the oxidative toxicity caused by high levels of glutamate. Here, we show that the small molecule proteostasis regulator AA147 protects against glutamate-induced cell death in a neuronal-derived cell culture model by reducing intracellular levels of reactive oxygen species. While originally developed as an activator of the ATF6 arm of the unfolded protein response, we show AA147-dependent protection against glutamate toxicity is primarily mediated through activation of the NRF2-regulated oxidative stress response. We demonstrate that AA147 activates NRF2 through a mechanism involving metabolic activation to a reactive electrophile and covalent modification of KEAP1 - a mechanism analogous to that involved in AA147-dependent activation of ATF6. These results define the potential for AA147 to protect against glutamate induced oxidative toxicity and highlight the potential for metabolically-activated proteostasis regulators like AA147 to activate both protective ATF6 and NRF2 stress-responsive signaling pathways to mitigate oxidative damage associated with diverse neurologic diseases.

biochemistry↗

bioRxiv2020

Pharmacologic IRE1/XBP1s Activation Promotes Systemic Adaptive Remodeling in Obesity

In obesity, overexpression of the IRE1-regulated transcription factor XBP1s protects against metabolic dysfunction by stimulating adaptive remodeling of multiple tissues, most notably the liver.1-5 This observation suggests that pharmacologically increasing IRE1/XBP1s signaling might be an attractive approach to mitigate pathologies in obesity and its associated complications.6-8 Here, we tested this notion by treating diet-induced obese (DIO) mice with the pharmacologic IRE1/XBP1s activator IXA4.9 We show that IXA4 treatment selectively activated protective IRE1/XBP1s signaling in livers of DIO mice without inducing obesity-linked pathologies associated with IRE1 hyperactivity, such as liver inflammation and fibrosis.10,11 Chronic IXA4 treatment improved systemic glucose metabolism and feeding-induced insulin action in the liver of DIO mice. These improvements were linked to IRE1/XBP1s-induced remodeling of the liver transcriptome, which dampened glucose production and reduced hepatic steatosis. Further, we show that IXA4 treatment enhanced pancreatic {beta} cell function and insulin homeostasis, indicating that systemic activation of IRE1/XBP1s signaling engendered multi-tissue benefits that integrated to mitigate systemic metabolic dysfunction in DIO mice. Our findings show that selective pharmacological activation of protective IRE1/XBP1s signaling reprograms multiple metabolic tissues, such as liver and pancreas, and represents a potential strategy to correct metabolic alterations in obesity.

physiology↗

bioRxiv2020

Structures of the Human LONP1 Protease Reveal Regulatory Steps Involved in Protease Activation

The human mitochondrial AAA+ protein LONP1 is a critical quality control protease involved in regulating diverse aspects of mitochondrial biology including proteostasis, electron transport chain activity, and mitochondrial transcription. As such, genetic or aging-associated imbalances in LONP1 activity are implicated in the pathologic mitochondrial dysfunction associated with numerous human diseases. Despite this importance, the molecular basis for LONP1-dependent proteolytic activity remains poorly defined. Here, we solved cryo-electron microscopy structures of human LONP1 to reveal the molecular mechanism of substrate proteolysis. We show that, like bacterial Lon, human LONP1 adopts both an open and closed spiral staircase orientation dictated by the presence of substrate and nucleotide. However, unlike bacterial Lon, human LONP1 contains a second spiral staircase within its ATPase domain that engages substrate to increase interactions with the translocating peptide as it transits into the proteolytic chamber for proteolysis. Further, we show that substrate-bound LONP1 includes a second level of regulation at the proteolytic active site, wherein autoinhibition of the active site is only relieved by the presence of a peptide substrate. Ultimately, our results define a structural basis for human LONP1 proteolytic activation and activity, establishing a molecular framework to understand the critical importance of this protease for mitochondrial regulation in health and disease.

molecular biology↗

bioRxiv2020

Enforced dimerization between XBP1s and ATF6f enhances the protective effects of the unfolded protein response (UPR) in models of neurodegeneration

Alteration to endoplasmic reticulum (ER) proteostasis is observed on a variety of neurodegenerative diseases associated with abnormal protein aggregation. Activation of the unfolded protein response (UPR) enables an adaptive reaction to recover ER proteostasis and cell function. The UPR is initiated by specialized stress sensors that engage gene expression programs through the concerted action of the transcription factors ATF4, ATF6f, and XBP1s. Although UPR signaling is generally studied as unique linear signaling branches, correlative evidence suggests that ATF6f and XBP1s may physically interact to regulate a subset of UPR-target genes. Here, we designed an ATF6f-XBP1s fusion protein termed UPRplus that behaves as a heterodimer in terms of its selective transcriptional activity. Cell-based studies demonstrated that UPRplus has stronger an effect in reducing the abnormal aggregation of mutant huntingtin and alpha-synuclein when compared to XBP1s or ATF6 alone. We developed a gene transfer approach to deliver UPRplus into the brain using adeno-associated viruses (AAVs) and demonstrated potent neuroprotection in vivo in preclinical models of Parkinsons and Huntingtons disease. These results support the concept where directing UPR-mediated gene expression toward specific adaptive programs may serve as a possible strategy to optimize the beneficial effects of the pathway in different disease conditions.

neuroscience↗

bioRxiv2020

The Endoplasmic Reticulum Proteostasis Regulator ATF6 is Essential for Human Cone Photoreceptor Development

Dysregulation of the endoplasmic reticulum (ER) Unfolded Protein Response (UPR) is implicated in the pathology of many human diseases associated with ER stress. Inactivating genetic variants in the UPR regulator Activating Transcription Factor 6 (ATF6) cause severe congenital heritable vision loss in patients by an unknown pathomechanism. To investigate this, we generated retinal organoids from patient iPSCs carrying ATF6 disease-causing variants and ATF6 null hESCs generated by CRISPR. Interestingly, we found that cone photoreceptor cells in ATF6 mutant retinal organoids lacked inner and outer segments concomitant with absence of cone phototransduction gene expression; while rod photoreceptors developed normally. Adaptive optics retinal imaging of patients with disease-causing variants in ATF6 also showed absence of cone inner/outer segment structures but preserved rod structures, mirroring the phenotypes observed in our retinal organoids. These results reveal that ATF6 is essential for the formation of human cone photoreceptors, and associated absence of cone phototransduction components explains the severe visual impairment in patients with ATF6 -associated retinopathy. Moreover, we show that a selective small molecule ATF6 activator compound restores the transcriptional activity of ATF6 disease-causing variants and stimulates the growth of cone photoreceptors in patient retinal organoids, demonstrating that pharmacologic targeting of ATF6 signaling is a therapeutic strategy that needs to be further explored for blinding retinal diseases.

developmental biology↗

bioRxiv2020

Insulin-like growth factor 2 (IGF2) protects against Huntington's disease through the extracellular disposal of protein aggregates

Impaired neuronal proteostasis is a salient feature of many neurodegenerative diseases, highlighting alterations in the function of the endoplasmic reticulum (ER). We previously reported that targeting the transcription factor XBP1, a key mediator of the ER stress response, delays disease progression and reduces protein aggregation in various models of neurodegeneration. To identify disease-modifier genes that may explain the neuroprotective effects of XBP1 deficiency, we performed gene expression profiling of brain cortex and striatum of these animals and uncovered insulin-like growth factor 2 (Igf2) as the major upregulated gene. Here we studied the impact of IGF2 signaling on protein aggregation in models of Huntingtons disease (HD) as proof-of-concept. Cell culture studies revealed that IGF2 treatment decreases the load of intracellular aggregates of mutant huntingtin and a polyglutamine peptide. These results were validated using induced pluripotent stem cells (iPSC)-derived medium spiny neurons from HD patients. The reduction in the levels of mutant huntingtin was associated with a decrease in the half-life of the intracellular protein. The decrease in the levels of abnormal protein aggregation triggered by IGF2 were independent of the activity of autophagy and the proteasome pathways, the two main routes for mutant huntingtin clearance. Conversely, IGF2 signaling enhanced the secretion of soluble mutant huntingtin species through exosomes and microvesicles involving changes in actin dynamics. Administration of IGF2 into the brain of HD mice using gene therapy led to a significant decrease in the levels of mutant huntingtin in three different animal models. Moreover, analysis of human post-mortem brain tissue, and blood samples from HD patients showed a reduction of IGF2 level. This study identifies IGF2 as a relevant factor deregulated in HD, operating as a disease modifier that buffers the accumulation of abnormal protein aggregates. One sentence summaryIGF2 reduces the load of intracellular protein aggregates through the extracellular disposal of the mutant protein.

neuroscience↗

bioRxiv2020

Small Molecule ER Proteostasis Regulators Reduce Amyloidogenic Immunoglobulin Light Chain Secretion Through an On-Target, ATF6-Independent Mechanism

The plasma cell secretion and toxic aggregation of amyloidogenic immunoglobulin light chains (LCs) causes proteotoxicity in Light Chain Amyloidosis (AL). We recently identified endoplasmic reticulum (ER) proteostasis regulators such as compound 147 that reduce secretion and aggregation of LCs implicated in AL (Plate, Cooley et al., 2016). Compound 147 promotes adaptive ER proteostasis remodeling through a mechanism involving covalent modification of multiple protein disulfide isomerases (PDIs) and subsequent activation of the ATF6 unfolded protein response (UPR) -associated transcriptional signaling pathway (Paxman, Plate et al., 2018). Here, we show that the 147-dependent reduction in amyloidogenic LC secretion from AL patient plasma cells is independent of ATF6 activation, but instead requires on-target PDI modification. Our results reveal pharmacologic targeting of PDIs as a potential strategy to ameliorate AL-associated proteotoxicity and demonstrate that 147 can influence ER proteostasis through multiple on-target mechanisms including ATF6 activation and PDI modification. IMPACT STATEMENTThis study demonstrates the broad potential for endoplasmic reticulum proteostasis regulator compounds such as 147 to influence secretory proteostasis of disease-associated proteins through multiple on target mechanisms.

biochemistry↗