Jason S. Park

Ferroptosis: A Regulated Cell Death Nexus Linking Metabolism, Redox Biology, and Disease

Ferroptosis is a form of regulated cell death characterized by the iron-dependent accumulation of lipid hydroperoxides to lethal levels. Emerging evidence suggests that ferroptosis represents an ancient vulnerability caused by the incorporation of polyunsaturated fatty acids into cellular membranes, and cells have developed complex systems that exploit and defend against this vulnerability in different contexts. The sensitivity to ferroptosis is tightly linked to numerous biological processes, including amino acid, iron, and polyunsaturated fatty acid metabolism, and the biosynthesis of glutathione, phospholipids, NADPH, and coenzyme Q10. Ferroptosis has been implicated in the pathological cell death associated with degenerative diseases (i.e., Alzheimers, Huntingtons, and Parkinsons diseases), carcinogenesis, stroke, intracerebral hemorrhage, traumatic brain injury, ischemia-reperfusion injury, and kidney degeneration in mammals and is also implicated in heat stress in plants. Ferroptosis may also have a tumor-suppressor function that could be harnessed for cancer therapy. This Primer reviews the mechanisms underlying ferroptosis, highlights connections to other areas of biology and medicine, and recommends tools and guidelines for studying this emerging form of regulated cell death.

Bacterial Virulence Proteins as Tools to Rewire Kinase Pathways in Yeast and Immune Cells

Bacterial pathogens have evolved specific effector proteins that, by interfacing with host kinase signalling pathways, provide a mechanism to evade immune responses during infection. Although these effectors contribute to pathogen virulence, we realized that they might also serve as valuable synthetic biology reagents for engineering cellular behaviour. Here we exploit two effector proteins, the Shigella flexneri OspF protein and Yersinia pestis YopH protein, to rewire kinase-mediated responses systematically both in yeast and mammalian immune cells. Bacterial effector proteins can be directed to inhibit specific mitogen-activated protein kinase pathways selectively in yeast by artificially targeting them to pathway-specific complexes. Moreover, we show that unique properties of the effectors generate new pathway behaviours: OspF, which irreversibly inactivates mitogen-activated protein kinases, was used to construct a synthetic feedback circuit that shows novel frequency-dependent input filtering. Finally, we show that effectors can be used in T cells, either as feedback modulators to tune the T-cell response amplitude precisely, or as an inducible pause switch that can temporarily disable T-cell activation. These studies demonstrate how pathogens could provide a rich toolkit of parts to engineer cells for therapeutic or biotechnological applications.

Synthetic control of mammalian-cell motility by engineering chemotaxis to an orthogonal bioinert chemical signal

Significance Directed migration of diverse cell types is critical in biological processes ranging from development and morphogenesis to immune response, wound healing, and regeneration. However, techniques to specifically and easily direct, manipulate, and study cell migration in vitro and in vivo are currently limited. We conceived of a strategy to directly control cell migration to arbitrary user-defined locations, independent of native chemotaxis receptors. In this work, we demonstrate that genetic modification of cells with an engineered G protein-coupled receptor allows us to redirect their migration to a bioinert drug-like small molecule, clozapine-N-oxide. This technology provides a generalizable tool to systematically control cell migration in vitro and in vivo and could be a valuable module for engineering future therapeutic cellular devices. Directed migration of diverse cell types plays a critical role in biological processes ranging from development and morphogenesis to immune response, wound healing, and regeneration. However, techniques to direct, manipulate, and study cell migration in vitro and in vivo in a specific and facile manner are currently limited. We conceived of a strategy to achieve direct control over cell migration to arbitrary user-defined locations, independent of native chemotaxis receptors. Here, we show that genetic modification of cells with an engineered G protein-coupled receptor allows us to redirect their migration to a bioinert drug-like small molecule, clozapine-N-oxide (CNO). The engineered receptor and small-molecule ligand form an orthogonal pair: The receptor does not respond to native ligands, and the inert drug does not bind to native cells. CNO-responsive migration can be engineered into a variety of cell types, including neutrophils, T lymphocytes, keratinocytes, and endothelial cells. The engineered cells migrate up a gradient of the drug CNO and transmigrate through endothelial monolayers. Finally, we demonstrate that T lymphocytes modified with the engineered receptor can specifically migrate in vivo to CNO-releasing beads implanted in a live mouse. This technology provides a generalizable genetic tool to systematically perturb and control cell migration both in vitro and in vivo. In the future, this type of migration control could be a valuable module for engineering therapeutic cellular devices.

Actin dynamics rapidly reset chemoattractant receptor sensitivity following adaptation in neutrophils

Neutrophils are cells of the innate immune system that hunt and kill pathogens using directed migration. This process, known as chemotaxis, requires the regulation of actin polymerization downstream of chemoattractant receptors. Reciprocal interactions between actin and intracellular signals are thought to underlie many of the sophisticated signal processing capabilities of the chemotactic cascade including adaptation, amplification and long-range inhibition. However, with existing tools, it has been difficult to discern actins role in these processes. Most studies investigating the role of the actin cytoskeleton have primarily relied on actin-depolymerizing agents, which not only block new actin polymerization but also destroy the existing cytoskeleton. We recently developed a combination of pharmacological inhibitors that stabilizes the existing actin cytoskeleton by inhibiting actin polymerization, depolymerization and myosin-based rearrangements; we refer to these processes collectively as actin dynamics. Here, we investigated how actin dynamics influence multiple signalling responses (PI3K lipid products, calcium and Pak phosphorylation) following acute agonist addition or during desensitization. We find that stabilized actin polymer extends the period of receptor desensitization following agonist binding and that actin dynamics rapidly reset receptors from this desensitized state. Spatial differences in actin dynamics may underlie front/back differences in agonist sensitivity in neutrophils.

Sinonasal Quality of Life in Children With Cystic Fibrosis

IMPORTANCE Sinusitis is the most common otolaryngologic complaint in children with cystic fibrosis (CF). However, basic knowledge about the effect of sinusitis on these children is lacking. OBJECTIVE To evaluate the incidence and quality-of-life impact of chronic rhinosinusitis (CRS) in an unbiased cohort of children with CF. DESIGN, SETTING, AND PARTICIPANTS Survey study of consecutive pediatric patients with CF presenting for routine quarterly evaluation at a tertiary CF clinic at an academic pediatric hospital. Surveys were completed during the period from December 2012 to January 2013. MAIN OUTCOMES AND MEASURES Surveys designed to assess major criteria for diagnosis of CRS and a validated pediatric sinonasal quality-of-life instrument, the Sinonasal-5 (SN-5). Statistical analysis was performed to evaluate association between demographic features and survey responses. RESULTS Of the 102 consecutive eligible patients, 47 children (46%) aged 2 to 20 years (mean [SD] age, 12.9 [5.6] years; 24 [51%] female) completed the surveys. Depending on the exact diagnostic criteria used, 5 (11%) to 18 (38%) of children with CF had CRS. Mean domain (2.16; 95% CI, 2.02-2.30) and overall visual-analog scale (8.26; 95% CI, 8.01-8.51) scores on the SN-5 were consistent with minimal effect on quality of life and comparable to historical posttreatment scores. Mean scores on nasal obstruction (3.07; 95% CI, 2.80-3.34) and sinusitis (2.68;; 95% CI, 2.42-2.94) were the most affected domains, whereas allergy (1.83; 95% CI, 1.65-2.01), emotional disturbance (1.76; 95% CI, 1.56-1.96), and activity restriction (1.43; 95% CI, 1.31-1.57) were minimally affected. Children with a diagnosis of CRS had higher mean SN-5 scores (2.60; 95% CI, 2.31-2.89 vs 2.05; 95% CI, 1.90-2.20; difference of 0.55; 95% CI, 0.29-0.80). Twenty-five patients (53%) had undergone some treatment for sinusitis. There was no association between SN-5 score and CRS treatment history. CONCLUSIONS AND RELEVANCE In this study, the incidence of symptomatic CRS was high, but quality-of-life impact was relatively low among children with CF. Use of standardized assessment scales, including consensus diagnostic criteria and validated quality-of-life surveys, may be helpful to guide referral and management decisions.

Impact of Primary Language and Insurance on Pediatric Hearing Health Care in a Multidisciplinary Clinic

Objective This study aims to describe the effects of primary language and insurance status on care utilization among deaf or hard-of-hearing children under active otolaryngologic and audiologic care. Study Design Cross-sectional analysis. Setting Multidisciplinary hearing loss clinic at a tertiary center. Subjects and Methods Demographics, hearing loss data, and validated survey responses were collected from 206 patients aged 0 to 19 years. Two-sided t tests and χ2 tests were used to obtain descriptive statistics and hypothesis testing. Results Of the sample, 52.4% spoke primarily English at home. Non-English-speaking children and families were less likely to receive psychiatric counseling (12.2% vs 35.2% in the English group, P < .001) and reported more difficulty obtaining educational interventions (P = .016), and 68.9% had public insurance. Parents of publicly insured children were less likely to know the type or degree of their child’s hearing loss (56.9% vs 75.4%, P = .022), and these children were older on presentation to the clinic (8.5 vs 6.5 years of age, P = .01) compared to privately insured children. Publicly insured children were less likely to receive cochlear implants (P = .046) and reported increased difficulty obtaining hearing aids (P = .047). While all patients reported impairment in hearing-related quality of life, publicly insured children aged 2 to 7 years were more likely to perform below minimum thresholds on measures of auditory/oral functioning. Conclusion Even when under active care, deaf or hard-of-hearing children from families who do not speak English at home or with public insurance face more difficulty obtaining educational services, cochlear implants, and hearing aids. These findings represent significant disparities in access to necessary interventions.