Engineering better bacterial backstabbers
Researchers at the University of California at Los Angeles have published the structure of pyocin R2, a protein nanomachine used by Pseudomonas aeruginosa to “stab” rival bacteria by punching holes in their cell membranes. It is one example of a contractile nanotube-based machine, a family of proteins used by bacteria, viruses and bacteriophages to inject DNA or proteins through cell membranes. Different members of the protein family have different mechanisms for delivering their payloads, and the authors used X-ray crystallography and electron microscopy to compare the structure of pyocin R2 to develop a model of how it delivers its payload. “By comparing these structures, we derived and tested a model for the action of a bactericidal nanomachine that couples specific recognition of target cells with deployment of a generic mechanism of killing, providing insights that are crucial for exploiting these structures as precision antimicrobials,” the authors wrote. They published their study in the April 15, 2020, issue of Nature.
Targeting bystander protein improves sepsis outcome
Investigators at The Feinstein Institutes for Medical Research have shown that by blocking the interaction of tetranectin with high-mobility group box 1 (HMGB1), a mediator of late-stage damage in sepsis, they were able to improve survival in an animal model. The team used a proteomic analysis of sepsis patients’ blood to demonstrate that they had lower tetranectin levels than healthy controls. Investigating the molecular mechanisms of their finding, they showed that tetranectin bound to HMGB1, leading macrophages to engulf the protein complex. HMGB1 has protective effects when it is located intracellularly, but deleterious effects when it is in the bloodstream, and its interaction with tetranectin tipped the scales in favor of its protective effects. The authors of an accompanying commentary pointed out that in addition to its specific findings on tetranectin and HGMB1, the paper “demonstrates how a bedside to bench to in vitro approach can identify unexpected biological targets that are altered in septic patients and hold notable translational promise.” Paper and commentary were published in the April 15, 2020, issue of Science Translational Medicine.
Long noncoding RNA has sex-specific role in depression
Scientists at the Mount Sinai School of Medicine have identified a primate-specific long noncoding RNA (lncRNA) that was down-regulated in the prefrontal cortex of females but not males with depression, and could induce resilience in female mice when it was delivered via viral vector. Twice as many females as males suffer from depression, which may be due to differences in stress resilience. LncRNAs are a class of gene expression regulatory RNAs. More than 40% of primate lncRNAs are primate-specific, and they are overrepresented in the brain, prompting the researchers to look for potential roles in depression. They showed that the long intergenic noncoding RNA (lincRNA) linc00473 was specifically down-regulated in postmortem brain samples of depressed females, and viral administration of the lincRNA00472 sequence could induce “stress resilience solely in female mice. This sex-specific phenotype was accompanied by changes in synaptic function and gene expression selectively in female mice,” the authors wrote. “Together, our studies identify LINC00473 as a female-specific driver of stress resilience that is aberrant in female depression.” They reported their findings in the April 16, 2020, online issue of Neuron.
Targeted IL-12 heats up cold tumors
How to convert immunologically cold tumors that do not respond to checkpoint blockade into hot, responsive tumors is a key question in antitumor immunotherapy. Now, researchers at the University of Chicago have mitigated IL-12 toxicity by fusing it to a collagen-binding domain, thus targeting it to tumor stroma. IL-12 is a cytokine that strongly activates both the innate and adaptive arms of the immune system. Administration of free IL-12 is highly toxic. A fusion protein of IL-12 and a collagen-binding protein has been more promising but needs to be injected intratumorally, prompting the authors to search for a fusion partner that would allow intravenous delivery. They fused the collagen-binding domain of the clotting cascade protein von Willebrand (vWF) factor to IL-12. Due to blood vessel leakiness that exposes collagen, vWF can accumulate in tumors. The authors showed that their fusion protein could elicit complete regression of checkpoint inhibition-resistant breast tumors in mouse models. They reported their results in the April 13, 2020, online issue of Nature Biomedical Engineering.
Fast route from fibroblasts to photoreceptors
Researchers at Circ Therapeutics have identified a small-molecule cocktail that could directly reprogram fibroblasts into photoreceptor cells that restored limited visual ability when they were transplanted into blind mice. Direct reprogramming of fibroblasts into another cell type rather than indirect reprogramming via a stem cell-like intermediate is a much faster process, but identifying small molecules for direct reprogramming into sensory neurons has been a challenge. In their experiments, the authors identified a cocktail of five small molecules that could reprogram fibroblasts into chemically induced photoreceptor-like cells (CiPCs). Transplantation of those cells into blind mice led to pupil constriction in slightly more than 40% of transplanted animals, and animals who developed pupil reflexes also showed signs of light-sensing ability. The authors concluded that “CiPCs could have therapeutic potential for restoring vision.” Their work appeared in the April 16, 2020, issue of Nature.
Eating pro-inflammatory IgG helps prevent liver failure
As chronic liver disease progresses to cirrhosis, immune system monocytes and macrophages can contribute to acute inflammation, leading to acute-on-chronic liver failure. Researchers at the French INSERM have demonstrated that inducing an atypical form of autophagy, LC3-associated phagocytosis (LAP), could protect rodents with chronic liver injuries from inflammation. LAP is a form of autophagy that specifically removes inflammation-promoting immunoglobulin G (IgG), triggering signaling by the anti-inflammatory immunoreceptor tyrosine-based activation motif (ITAMi) pathway. The authors concluded that “these data suggest that sustaining LAP in patients with cirrhosis might prevent progression to a syndrome that is associated with a high mortality rate.” They reported their results in the April 15, 2020, issue of Science Translational Medicine.
Depression’s structural problem
Researchers from the University of Illinois at Chicago have discovered that tubulin acetylation was altered in the postmortem brains of depressed individuals, both those who died of suicide and those who died of other causes. Antidepressant medications target neurotransmitter systems, but they are only effective for about half of depressed individuals. Previous studies had implicated microtubules, which are structural proteins of the cytoskeleton, in neuropsychiatric disorders. Microtubules play a role in both synaptic structure and molecular transport through cells. In their work, the authors showed that changes to epigenetic acetyl tags on tubulin, which affected the location of the G protein Gαs and the function of the intracellular signaling molecule cyclic adenosine monophosphate (cAMP). The team reported its results in the April 6, 2020, issue of the Journal of Neuroscience.
Modeling the post-infarct heart
Researchers at Clemson University have developed a cardiac organoid that modeled the human heart after suffering a heart attack. Organoids, three-dimensional culture systems of multiple cell types, have emerged as powerful model systems for the study of development and genetic disorders. However, environmental contributors are a major factor in cardiovascular disease. In particular, low oxygenation and fibrosis drive the progression to heart failure after a heart attack. The authors “leveraged nutrient transport principles (namely, oxygen diffusion) in 3D microtissues along with chronic adrenergic stimulation to create a gradient of apoptotic center – dysfunctional interior – functional edge in human cardiac organoids, which recapitulated the infarct, border, remote zones, respectively, of infarct hearts.” The authors wrote they were able to “recapitulate hallmarks of myocardial infarction (in particular, pathological metabolic shifts, fibrosis and calcium handling) at the transcriptomic, structural and functional levels… [and] model hypoxia-enhanced doxorubicin cardiotoxicity.” They concluded, “Human organoids that model diseases with non-genetic pathological factors could help with drug screening and development.” They published their results in the April 13, 2020, online issue of Nature Biomedical Engineering.
Interleukins rile each other up in reaction to implants
Researchers at Johns Hopkins University have identified a vicious cycle between interleukin 17 (IL-17) and senescent cells in the fibrotic encapsulation of medical implants. Despite being engineered in part to minimize immune responses, implants are recognized by the immune system, which reacts by forming a fibrous capsule around them. This response can interfere with the functioning of the implant, and in some cases, the implant can set off systemic immune responses. The authors analyzed fibrotic capsules that had formed around silicone breast implants, necessitating their removal. They showed that such capsules had high numbers of IL-17-producing T cells, and high levels of senescent cells. Investigation in animal and cell culture models showed that IL-17 induced senescence, and senescent cells secreted IL-6 that further stimulated IL-17 production from T cells. The authors concluded that “discovery of a feed-forward loop between the [IL-17-producing] immune response and the senescence response to implanted synthetic materials introduces new targets for therapeutic intervention” in the reaction to medical implants. Their work appeared in the April 15, 2020, issue of Science Translational Medicine.
Complement links high BMI to dementia
A high body mass index (BMI) in midlife has been causally linked to an increased risk of dementia in old age, independently of the effects of physical inactivity. Researchers at the Jackson Laboratories have identified the complement system component C1q as a link between high BMI and dementia. The complement system is a highly pro-inflammatory component of the innate immune system. The authors showed that “genetic deletion of the complement component C1QA prevents cerebrovascular damage, neuroinflammation and white matter degradation in a mouse model of western diet-induced obesity, demonstrating that inflammatory responses play a significant role in obesity-induced brain pathology. The complement pathway is an attractive therapeutic target to prevent cognitive decline and reduction of dementia risk caused by obesity.” Their findings were published in the April 13, 2020, issue of eNeuro.