Mitochondria shed their outer membrane in response to infection-induced stress

Mitochondria shed their SPOTs Outer mitochondrial membrane (OMM) function is essential for cellular health. How mitochondria respond to naturally occurring OMM stress is unknown. Li et al . show that, upon infection with the human parasite Toxoplasma gondii , mitochondria shed large structures positive for OMM (SPOTs). SPOT formation required the parasite effector TgMAF1 and its interaction with the host mitochondrial receptor TOM70 and translocase SAM50. TOM70-dependent SPOT formation mediated a depletion of mitochondrial proteins and optimal parasite growth. SPOT-like structures also formed after OMM perturbations independently of infection. Thus, membrane remodeling is a feature of cellular responses to OMM stress that Toxoplasma hijacks during infection. —SMH

SARS-CoV-2 Humoral and Cellular Immune Responses in COVID-19 Convalescent Individuals With HIV

Background SARS-CoV-2-specific immune response features in people with HIV infection (PWH) remain to be fully elucidated. We aimed to evaluate the impact of HIV over humoral and cellular responses in COVID-19 convalescent PWH. Methods Blood samples from 29 PWH with preserved CD4+T-cell counts on ART and 29 HIV-negative (HIVneg) donors were included. SARS-CoV-2-specific IgG levels and IgG titers were determined by ELISA. Antibody neutralization capacity was evaluated against the reference B1 strain SARS-CoV-2. IFN-γ-secreting cells were detected by ELISpot using SARS-CoV-2 Spike, RBD, or Nucleocapsid protein or overlapping peptide pools. Frequency and phenotype of T, B and NK cells and levels of soluble cytokines and chemokines were assessed by flow cytometry. Results SARS-CoV-2-specific antibodies were detected on 65.5% of PWH and 79.3% of HIVneg individuals, with no differences in serum IgG levels and anti-SARS-CoV-2 neutralizing antibodies. All donors exhibited SARS-CoV-2-specific cellular immunity, including those with undetectable antibody responses. PWH showed diminished percentages of antibody-secreting cells compared to HIVneg cohort, with similar B cell proportions between groups. PWH presented an increment in T follicular helper (Tfh, CD4+CXCR5+) percentage, which negatively correlated with IgG titers. Additionally, CD4+PD1+ and CD8+HLA-DR+ cell frequencies were augmented in PWH. Moreover, PWH presented a high proportion of CD95+, CD25+, NKp46+, HLA-DR+, and CD38+/HLA-DR+ NK cells. Both groups displayed similar Tregs frequency, effector/memory, and T-helper profile for CD4TL, exhaustion and memory phenotypes for CD8TL and subtle differences in classical monocytes. Profile of circulating cytokines and chemokines was significantly different between both groups. Magnitude of IFN-γ responses to S or N proteins, and RBD was lower in PWH compared to HIVneg donors. Correlation analysis of immune and clinical parameters showed a distinct immune landscape in the PWH group. Conclusions PWH showed a distinctive immune profile although severity of COVID-19 was not exacerbated. PWH with conserved CD4+T-cell counts exerted both humoral and cellular responses against SARS-CoV-2. Even though cellular response was lower compared to HIVneg individuals, PWH achieved similar antibody responses with a high neutralization capacity. These data reinforce the impact of ART, not only in controlling HIV but also other infections.

Image based annotation of Chemogenomic Libraries for Phenotypic Screening

Phenotypical screening is a widely used approach in drug discovery for the identification of small molecules with cellular activities. However, functional annotation of identified hits often poses a challenge. The development of small molecules with narrow or exclusive target selectivity such as chemical probes and chemogenomic (CG) libraries, greatly diminishes this challenge, but non-specific effects caused by compound toxicity or interference with basic cellular functions still poses a problem to associate phenotypic readouts with molecular targets. Hence, each compound should ideally be comprehensively characterized regarding its effects on general cell functions. Here, we report an optimized live-cell multiplexed assay that classifies cells based on nuclear morphology, presenting an excellent indicator for cellular responses such as early apoptosis and necrosis. This basic readout in combination with the detection of other general cell damaging activities of small molecules such as changes in cytoskeletal morphology, cell cycle and mitochondrial health provides a comprehensive time-dependent characterization of the effect of small molecules on cellular health in a single experiment. The developed high-content assay offers multi-dimensional comprehensive characterization that can be used to delineate generic effects regarding cell functions and cell viability, allowing an assessment of compound suitability for subsequent detailed phenotypic and mechanistic studies.

Bias in FGFR1 signaling in response to FGF4, FGF8, and FGF9

FGFR1 signals differently in response to the FGF ligands FGF4, FGF8 and FGF9, but the mechanism behind the differential ligand recognition is poorly understood. Here, we use biophysical tools to quantify multiple aspects of FGFR1 signaling in response to the three FGFs: potency, efficacy, ligand-induced oligomerization and downregulation, and conformation of the active FGFR1 dimers. We show that FGF4, FGF8, and FGF9 are biased ligands, and that bias can explain differences in FGF8 and FGF9-mediated cellular responses. Our data suggest that ligand bias arises due to structural differences in the ligand-bound FGFR1 dimers, which impact the interactions of the FGFR1 transmembrane helices, leading to differential recruitment and activation of the downstream signaling adaptor FRS2. This study expands the mechanistic understanding of FGF signaling during development and brings the poorly understood concept of receptor tyrosine kinase ligand bias into the spotlight.

Toward Multiplexed Optogenetic Circuits

Owing to its ubiquity and easy availability in nature, light has been widely employed to control complex cellular behaviors. Light-sensitive proteins are the foundation to such diverse and multilevel adaptive regulations in a large range of organisms. Due to their remarkable properties and potential applications in engineered systems, exploration and engineering of natural light-sensitive proteins have significantly contributed to expand optogenetic toolboxes with tailor-made performances in synthetic genetic circuits. Progressively, more complex systems have been designed in which multiple photoreceptors, each sensing its dedicated wavelength, are combined to simultaneously coordinate cellular responses in a single cell. In this review, we highlight recent works and challenges on multiplexed optogenetic circuits in natural and engineered systems for a dynamic regulation breakthrough in biotechnological applications.