Persistent tailoring of MSC activation through genetic priming

Mesenchymal stem/stromal cells (MSCs) are an attractive platform for cell therapy due to their safety profile and unique ability to secrete broad arrays of immunomodulatory and regenerative molecules. Yet, MSCs are well known to require preconditioning or priming to boost their therapeutic efficacy. Current priming methods offer limited control over MSC activation, yield transient effects, and often induce expression of pro-inflammatory effectors that can potentiate immunogenicity. Here, we describe a 'genetic priming' method that can both selectively and sustainably boost MSC potency via the controlled expression of the inflammatory-stimulus-responsive transcription factor IRF1 (interferon response factor 1). MSCs engineered to hyper-express IRF1 recapitulate many core responses that are accessed by biochemical priming using the proinflammatory cytokine interferon-γ (IFNγ). This includes the upregulation of anti-inflammatory effector molecules and the potentiation of MSC capacities to suppress T cell activation. However, we show that IRF1-mediated genetic priming is much more persistent than biochemical priming and can circumvent IFNγ-dependent expression of immunogenic MHC class II molecules. Together, the ability to sustainably activate and selectively tailor MSC priming responses creates the possibility of programming MSC activation more comprehensively for therapeutic applications.

Bacillus Calmette-Guérin vaccination as defense against SARS-CoV-2 (BADAS): a randomized controlled trial to protect healthcare workers in the USA by enhanced trained immune responses

BACKGROUND

A large epidemic, such as that observed with SARS-CoV-2, seriously challenges available hospital capacity, and this would be augmented by infection of healthcare workers (HCW). Bacillus Calmette-Guérin (BCG) is a vaccine against tuberculosis, with protective non-specific effects against other respiratory tract infections in vitro and in vivo. Preliminary analyses suggest that regions of the world with existing BCG vaccination programs have lower incidence and mortality from COVID-19. We hypothesize that BCG vaccination can reduce SARS-CoV-2 infection and disease severity.

METHODS

This will be a placebo-controlled adaptive multi-center randomized controlled trial. A total of 1800 individuals considered to be at high risk, including those with comorbidities (hypertension, diabetes, obesity, reactive airway disease, smokers), racial and ethnic minorities, elderly, teachers, police, restaurant wait-staff, delivery personnel, health care workers who are defined as personnel working in a healthcare setting, at a hospital, medical center or clinic (veterinary, dental, ophthalmology), and first responders (paramedics, firefighters, or law enforcement), will be randomly assigned to two treatment groups. The treatment groups will receive intradermal administration of BCG vaccine or placebo (saline) with groups at a 1:1 ratio. Individuals will be tracked for evidence of SARS-CoV-2 infection and severity as well as obtaining whole blood to track immunological markers, and a sub-study will include cognitive function and brain imaging. The majority of individuals will be followed for 6 months, with an option to extend for another 6 months, and the cognitive sub-study duration is 2 years. We will plot Kaplan-Meier curves that will be plotted comparing groups and hazard ratios and p-values reported using Cox proportional hazard models.

DISCUSSION

It is expected this trial will allow evaluation of the effects of BCG vaccination at a population level in high-risk healthcare individuals through a mitigated clinical course of SARS-CoV-2 infection and inform policy making during the ongoing epidemic.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04348370. Registered on April 16, 2020.

Interleukin-18 as a severity marker and novel potential therapeutic target for epidermolytic ichthyosis

BACKGROUND

Epidermolytic ichthyosis (EI) is a major form of nonsyndromic inherited ichthyosis, characterized by erythroderma, marked hyperkeratosis and scale, bulla and erosion at birth, associated with KRT1/KRT10 mutations. The cytokine and chemokine profiles in EI are poorly understood, and specific treatment options have not been established.

AIM

To explore novel biomarkers and therapeutic targets in patients with EI.

METHODS

We analysed cytokine levels in serum and skin samples from 10 patients with inherited ichthyosis, including seven patients with EI. Wild-type and mutant KRT1 constructs were established and transfected into HaCaT cells, an immortalized keratinocyte cell line, for in vitro immunoblotting and immunocytochemistry analyses.

RESULTS

Multiplex cytokine/chemokine analysis revealed that 10 cytokines/chemokines [interleukin (IL)-1β, IL-4, IL-17A, IL-16, IL-18, IL-1 receptor-α, macrophage colony-stimulating factor, interferon-α2, basic fibroblast growth factor and monocyte chemotactic protein-3] were significantly increased in patients with EI. Furthermore, IL-18 levels were significantly higher in patients with EI [n = 7; 2714.1 (1438.0) pg mL-1] than in healthy controls [n = 11; 218.4 (28.4) pg mL-1, P < 0.01]. Immunohistochemical analyses showed that IL-18 expression was elevated in skin samples from patients with EI. Serum IL-18 levels correlated with the severity of ichthyosis, as measured by the Ichthyosis Scoring System. Immunoblotting analysis revealed that mature IL-18 levels were increased in the supernatant of mutant KRT1 expressing HaCaT cells. Additionally, these cells showed NLRP3 aggregation in the cytoplasm and ASC clustered around mutant keratin aggregations. These findings suggest that mutant keratin might promote the activation of the NLRP3 inflammasome and its downstream caspase-1-mediated IL-18 release in keratinocytes from patients with EI.

CONCLUSIONS

Our results suggest that serum IL-18 is a severity marker released from the skin of patients with EI. Blockade of IL-18 may be a useful novel therapeutic option for patients with EI.

Targeting TCA cycle metabolites by small molecule inhibitors ameliorate LPS induced immune tolerance in Macrophages through epigenetic mechanisms

Background

Severe and chronic infections, such as sepsis and Tuberculosis, result in macrophage immune tolerance in order to prevent pathologic inflammation. Immune tolerance is believed to be a result of metabolic dysregulation, especially of the TCA cycle. Metabolites play a critical role in regulating epigenetic mechanism, but many aspects remain poorly understood.

Methods

An in-vitro LPS tolerance model was used to evaluate if manipulating the TCA cycle could mitigate immune tolerance. Intracellular signaling, DNA methylation, and nuclear localization were measured using RPPA, Illumina EPIC, and confocal microscopy, respectively.

Results

Metabolic inhibitors of glycolysis (metformin), the TCA cycle (BAY 1436032), and mTOR (rapamycin and everolimus) blocked LPS-induced immune tolerance. LPS treatment changed the methylome with hypermethylation of key genes of the TCA cycle including PDP2, NDUFS8, TRAP1 and PDK2 and lead to increased nuclear localization of the TCA enzymes, which could be ameliorated with inhibitors. Increased levels of key mediators of the TCA by LPS treatment including p-mTOR, pAKT, LDHA, IDH1, LC3A and epigenetic regulator p300 was significantly downregulated by pre-treatment with metformin, everolimus and BAY 1436032. BAY 1436032 also significantly reduced the LPS induced upregulation of epigenetic enzymes including histone deacetylases (HDAC) 3,4, and EZH2.

Conclusion

Previous studies demonstrated that LPS induces epigenetic-mediated immune tolerance. Here we show this can be mitigated by inhibiting glycolysis, mTOR pathway and TCA cycle. This could have clinical implications in treatment of sepsis and Tuberculosis among other diseases.

Supported by NIAID K23 AI141681-02

Increased DNA methylation, cellular senescence and premature epigenetic aging in guinea pigs and humans with tuberculosis

Background: Tuberculosis (TB) is the archetypical chronic infection, with patients having months of symptoms before diagnosis. In the two years after successful therapy, survivors of TB have a three-fold increased risk of death.

Methods: Guinea pigs were infected with Mycobacterium tuberculosis (Mtb) for 45 days, followed by RRBS DNA methylation analysis. In humans, network analysis of differentially expressed genes across three TB cohorts were visualized at the pathway-level. Serum levels of inflammation were measured by ELISA. Horvath (DNA methylation) and RNA-seq biological clocks were used to investigate shifts in chronological age among humans with TB.

Results: Guinea pigs with TB demonstrated DNA hypermethylation and showed system-level similarity to humans with TB (p-value = 0.002). The transcriptome in TB in multiple cohorts was enriched for DNA methylation and cellular senescence. Senescence associated proteins CXCL9, CXCL10, and TNF were elevated in TB patients compared to healthy controls. Humans with TB demonstrate 12.7 years (95% CI: 7.5, 21.9) and 14.38 years (95% CI: 10.23–18.53) of cellular aging as measured by epigenetic and gene expression based cellular clocks, respectively.

Conclusions: In both guinea pigs and humans, TB perturbs epigenetic processes, promoting premature cellular aging and inflammation, a plausible means to explain the long-term detrimental health outcomes after TB.

Gene expression signatures identify biologically and clinically distinct tuberculosis endotypes

BACKGROUND

In vitro, animal model, and clinical evidence suggests that tuberculosis is not a monomorphic disease, and that host response to tuberculosis is protean with multiple distinct molecular pathways and pathologies (endotypes). We applied unbiased clustering to identify separate tuberculosis endotypes with classifiable gene expression patterns and clinical outcomes.

METHODS

A cohort comprised of microarray gene expression data from microbiologically confirmed tuberculosis patients were used to identify putative endotypes. One microarray cohort with longitudinal clinical outcomes was reserved for validation, as was two RNA-seq cohorts. Finally, a separate cohort of tuberculosis patients with functional immune responses was evaluated to clarify stimulated from unstimulated immune responses.

RESULTS

A discovery cohort, including 435 tuberculosis patients and 533 asymptomatic controls, identified two tuberculosis endotypes. Endotype A is characterised by increased expression of genes related to inflammation and immunity and decreased metabolism and proliferation; in contrast, endotype B has increased activity of metabolism and proliferation pathways. An independent RNA-seq validation cohort, including 118 tuberculosis patients and 179 controls, validated the discovery results. Gene expression signatures for treatment failure were elevated in endotype A in the discovery cohort, and a separate validation cohort confirmed that endotype A patients had slower time to culture conversion, and a reduced cure rate. These observations suggest that endotypes reflect functional immunity, supported by the observation that tuberculosis patients with a hyperinflammatory endotype have less responsive cytokine production upon stimulation.

CONCLUSION

These findings provide evidence that metabolic and immune profiling could inform optimisation of endotype-specific host-directed therapies for tuberculosis.

Reversing Post-Infectious Epigenetic-Mediated Immune Suppression

The immune response must balance the pro-inflammatory, cell-mediated cytotoxicity with the anti-inflammatory and wound repair response. Epigenetic mechanisms mediate this balance and limit host immunity from inducing exuberant collateral damage to host tissue after severe and chronic infections. However, following treatment for these infections, including sepsis, pneumonia, hepatitis B, hepatitis C, HIV, tuberculosis (TB) or schistosomiasis, detrimental epigenetic scars persist, and result in long-lasting immune suppression. This is hypothesized to be one of the contributing mechanisms explaining why survivors of infection have increased all-cause mortality and increased rates of unrelated secondary infections. The mechanisms that induce epigenetic-mediated immune suppression have been demonstrated in-vitro and in animal models. Modulation of the AMP-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR), nuclear factor of activated T cells (NFAT) or nuclear receptor (NR4A) pathways is able to block or reverse the development of detrimental epigenetic scars. Similarly, drugs that directly modify epigenetic enzymes, such as those that inhibit histone deacetylases (HDAC) inhibitors, DNA hypomethylating agents or modifiers of the Nucleosome Remodeling and DNA methylation (NuRD) complex or Polycomb Repressive Complex (PRC) have demonstrated capacity to restore host immunity in the setting of cancer-, LCMV- or murine sepsis-induced epigenetic-mediated immune suppression. A third clinically feasible strategy for reversing detrimental epigenetic scars includes bioengineering approaches to either directly reverse the detrimental epigenetic marks or to modify the epigenetic enzymes or transcription factors that induce detrimental epigenetic scars. Each of these approaches, alone or in combination, have ablated or reversed detrimental epigenetic marks in in-vitro or in animal models; translational studies are now required to evaluate clinical applicability.

Tuberculosis endotypes to guide stratified host-directed therapy

There is hope that host-directed therapy (HDT) for Tuberculosis (TB) can either shorten treatment duration, help cure drug resistant disease or limit the immunopathology. Many candidate HDT drugs have been proposed, however solid evidence only exists for a few select patient groups. The clinical presentation of TB is variable, with differences in severity, tissue pathology, and bacillary burden. TB clinical phenotypes likely determine the potential benefit of HDT. Underlying TB clinical phenotypes, there are TB "endotypes," defined as distinct molecular profiles, with specific metabolic, epigenetic, transcriptional, and immune phenotypes. TB endotypes can be characterized by either immunodeficiency or pathologic excessive inflammation. Additional factors, like comorbidities (HIV, diabetes, helminth infection), structural lung disease or Mycobacterial virulence also drive TB endotypes. Precise disease phenotyping, combined with in-depth immunologic and molecular profiling and multimodal omics integration, can identify TB endotypes, guide endotype-specific HDT, and improve TB outcomes, similar to advances in cancer medicine.

Disseminated cryptococcosis and anti-granulocyte-macrophage colony-stimulating factor autoantibodies: An underappreciated association

The development of disseminated cryptococcosis has historically occurred in patients living with advanced human immunodeficiency virus or other immunosuppressive conditions affecting T-cell function. Recently, patients with anti-cytokine neutralising autoantibodies have been recognised to be at risk for disseminated infections by opportunistic intracellular pathogens, including Cryptococcus species. Herein, we present a previously healthy 26-year-old man who was evaluated with disseminated cryptococcosis involving the bone, lung, mediastinum and brain. The patient's serum cryptococcal antigen titres were >1:1,100,000, and evaluation for an underlying immunodeficiency revealed high titres for anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) autoantibodies. We also review the literature of all published cases of disseminated cryptococcosis associated with the presence of anti-GM-CSF autoantibodies. Clinicians should have a heightened awareness of anti-cytokine autoantibodies in patients without a known immunodeficiency and development disseminated infections by opportunistic intracellular pathogens.

Perspective for Precision Medicine for Tuberculosis

Tuberculosis is a bacterial infectious disease that is mainly transmitted from human to human via infectious aerosols. Currently, tuberculosis is the leading cause of death by an infectious disease world-wide. In the past decade, the number of patients affected by tuberculosis has increased by ~20 percent and the emergence of drug-resistant strains of Mycobacterium tuberculosis challenges the goal of elimination of tuberculosis in the near future. For the last 50 years, management of patients with tuberculosis has followed a standardized management approach. This standardization neglects the variation in human susceptibility to infection, immune response, the pharmacokinetics of drugs, and the individual duration of treatment needed to achieve relapse-free cure. Here we propose a package of precision medicine-guided therapies that has the prospect to drive clinical management decisions, based on both host immunity and M. tuberculosis strains genetics. Recently, important scientific discoveries and technological advances have been achieved that provide a perspective for individualized rather than standardized management of patients with tuberculosis. For the individual selection of best medicines and host-directed therapies, personalized drug dosing, and treatment durations, physicians treating patients with tuberculosis will be able to rely on these advances in systems biology and to apply them at the bedside.

Synergetic Roles of Formyl Peptide Receptor 1 Oligomerization in Ligand-Induced Signal Transduction

G protein-coupled receptors (GPCRs) transduce extracellular signals into cells by interacting with G proteins and arrestins. Emerging evidence suggests that GPCRs on the plasma membrane are in a dynamic equilibrium among monomers, dimers, and larger oligomers. Nevertheless, the role of the oligomer formation in the GPCR signal transduction remains unclear. Using multicolor single-molecule live-cell imaging, we show a dynamic interconversion between small and large oligomer states of a chemoattractant GPCR, Formyl Peptide Receptor 1 (FPR1), and its binding affinity with G protein. Full agonist stimulation increased a fraction of large FPR1 oligomers, which allowed for prolonged FPR1-G protein interaction. The G protein interaction with FPR1 was most stabilized at the full agonist-bound large FPR1 oligomers. Based on these results, we propose that G protein-mediated signal transduction may be regulated synergistically by the ligand-binding and FPR1 oligomerization. Cooperative signal control induced by receptor oligomerization is anticipated as a target for drug discovery.

DNA hypermethylation during tuberculosis dampens host immune responsiveness

Mycobacterium tuberculosis (M. tuberculosis) has coevolved with humans for millennia and developed multiple mechanisms to evade host immunity. Restoring host immunity in order to improve outcomes and potentially shorten existing therapy will require identification of the full complement by which host immunity is inhibited. Perturbation of host DNA methylation is a mechanism induced by chronic infections such as HIV, HPV, lymphocytic choriomeningitis virus (LCMV), and schistosomiasis to evade host immunity. Here, we evaluated the DNA methylation status of patients with tuberculosis (TB) and their asymptomatic household contacts and found that the patients with TB have DNA hypermethylation of the IL-2/STAT5, TNF/NF-κB, and IFN-γ signaling pathways. We performed methylation-sensitive restriction enzyme-quantitative PCR (MSRE-qPCR) and observed that multiple genes of the IL-12/IFN-γ signaling pathway (IL12B, IL12RB2, TYK2, IFNGR1, JAK1, and JAK2) were hypermethylated in patients with TB. The DNA hypermethylation of these pathways was associated with decreased immune responsiveness with decreased mitogen-induced upregulation of IFN-γ, TNF, IL-6, CXCL9, CXCL10, and IL-1β production. The DNA hypermethylation of the IL-12/IFN-γ pathway was associated with decreased IFN-γ-induced gene expression and decreased IL-12-inducible upregulation of IFN-γ. This study demonstrates that immune cells from patients with TB are characterized by DNA hypermethylation of genes critical to mycobacterial immunity resulting in decreased mycobacteria-specific and nonspecific immune responsiveness.

Correlation of DNA Methylation Status and Immune Function in the Cytotoxic Immune Cells of Tuberculosis Patients

BACKGROUND

Less than 10% of individuals infected with Mtb develop disease. Similarly, in the pre-antibiotic era, ~20% of Tuberculosis (TB) patients overcame the disease. This implies host immunity can control Mtb infection. We evaluated the role of cytotoxic immune cells (CD8, CD56 and CD3+CD56+) among individuals with chronic infections that increase risk of TB progression.

METHODS

DNA Methyl EPIC was evaluated in patients with helminths, HIV and TB (n = 32) and flow-based immune phenotyping was implemented on 108 individuals. Gene expression of 717 TB patients and 525 healthy controls was downloaded from publicly available databases.

RESULTS

All evaluated cytotoxic cells displayed DNA methylation perturbations in the IL-2-STAT5, PI3K and IFNγ signaling pathways. TB patients experienced DNA hyper-methylation of perforin in CD56 NK cells and in granzyme A and granzyme B of CD8+ cytotoxic lymphocytes (CTLs). By flow cytometry TB patients up-regulated mycobacterial-specific perforin in CTLs while CD3−CD56+ NK cells expressed decreased perforin. Early evidence suggests that the increased perforin expression from CTLs was heterogenous and only occurs in ~46% of TB patients. Further evidence for heterogenous TB sub-groups was demonstrated by gene expression as 333 TB patients had increased perforin gene expression, while 313 had decreased gene expression (log2 fold change with FDR &lt; 1%).

CONCLUSION

To evaluate the DNA methylation-immune phenotype associations from this clinical cohort, mechanistic studies manipulating DNA methylation status are undergoing. Identifying how epigenetic modifications alter cytotoxic cells capacity to kill intracellular mycobacteria is critical to future host directed therapeutic options.

Age and HIV perturb the TB Immunity in Regulatory and Cytotoxic Subpopulations of NKT cells

In the pre-antibiotic era, ~20% of Tuberculosis (TB) patients overcame the disease without therapy, implying host immunity can sometimes control disease. The risk of disease progression is higher among HIV-infected individuals and children, therefore we evaluate how HIV and age alter the balance of cytotoxic versus immune regulatory NKT immune phenotype in individuals with TB and latent Mycobacterium tuberculosis infection (LTBi). We evaluated the NKT immune response from 49 individuals with TB (25 HIV-infected) and 48 with asymptomatic LTBi (14 HIV-infected). Using flow cytometry based multi-dimensional immune profiling, we analyzed the expression level of previously described determinants of NKT cytotoxicity (CD3dim) and immune regulatory (CD3bright) phenotype and function. CD3bright NKT cell population was correlated with age during children TB (p = 0.002). This cell type had increased in adults with TB (p = 0.034), but not in children. Also, high level of perforin producing CD3bright NKT cells had increased in adults with TB compare to adults with LTBi (p = 0.004). On the other hand, CD3dim NKT cell had no age correlation nor difference between TB and LTBi participants. While HIV-infected LTBi individuals had decreased perforin production in CD3dim NKT cells (p = 0.012). CD3bright and CD3dim NKT sub-populations previously reported influence regulatory versus cytotoxic function. We demonstrate that age and HIV status of participants have effected to regulatory and cytotoxic function, respectively. This suggested that these two factors have different mechanisms, decreasing perforin high producing CD3bright NKT cells and decreasing perforin production in CD3dim NKT, which promote TB disease progression.

Epigenetic mediated immune exhaustion persists after successful Tuberculosis therapy

BACKGROUND

Chronic antigen stimulation from HIV, HPV, LCMV and schistosomiasis induce epigenetic-mediated immune exhaustion. Individuals with successful anti-TB therapy (ATT) have a thirteen-fold increased risk of developing recurrent TB.

METHODS

From a cohort of HIV infected and uninfected individuals with TB and their asymptomatic household contacts (n=32), genome-wide DNA methylation (DNA MethylEPIC) and epigenetic deconvolution (EDEC) identified cell-specific DNA methylation. Cell-specific results were validated with MSRE-PCR, gene expression and flow cytometry-based Mtb-specific multi-dimensional immune profiling.

RESULTS

Participants with TB had DNA hypermethylation in the IL-2, TCR and IFN-γ signalling pathways. The IFN-γ signalling pathway was affected in both innate (NK cells and monocytes) as well as adaptive (CD4 and CD8 T cells) lineages. Select DNA hyper-methylated differences were validated using MSRE-PCR. Pioneer and Transcription factors critical for cell-mediated immunity were also significantly differentially methylated with enrichment scores compatible with previous epigenetic-mediated immune exhaustion. After overnight stimulation with IFN-γ, TB patients have decreased IFN-γ-inducible gene expression. Six months after the completion of successful ATT, participants with TB have persistent DNA hypermethylation.

DISCUSSION

Persistent DNA hypermethylation may be a potential mechanism by which individuals with TB are at increased risk of recurrent disease. This may also assist in identifying potential new targets for host-directed therapy.

Schistosomiasis Induces Persistent DNA Methylation and Tuberculosis-Specific Immune Changes

Epigenetic mechanisms, such as DNA methylation, determine immune cell phenotype. To understand the epigenetic alterations induced by helminth coinfections, we evaluated the longitudinal effect of ascariasis and schistosomiasis infection on CD4⁺ T cell DNA methylation and the downstream tuberculosis (TB)-specific and bacillus Calmette-Guérin-induced immune phenotype. All experiments were performed on human primary immune cells from a longitudinal cohort of recently TB-exposed children. Compared with age-matched uninfected controls, children with active Schistosoma haematobium and Ascaris lumbricoides infection had 751 differentially DNA-methylated genes, with 72% hypermethylated. Gene ontology pathway analysis identified inhibition of IFN-γ signaling, cellular proliferation, and the Th1 pathway. Targeted real-time quantitative PCR after methyl-specific endonuclease digestion confirmed DNA hypermethylation of the transcription factors BATF3, ID2, STAT5A, IRF5, PPARg, RUNX2, IRF4, and NFATC1 and cytokines or cytokine receptors IFNGR1, TNFS11, RELT (TNF receptor), IL12RB2, and IL12B (p < 0.001; Sidak-Bonferroni). Functional blockage of the IFN-γ signaling pathway was confirmed, with helminth-infected individuals having decreased upregulation of IFN-γ-inducible genes (Mann-Whitney p < 0.05). Hypomethylation of the IL-4 pathway and DNA hypermethylation of the Th1 pathway was confirmed by Ag-specific multidimensional flow cytometry demonstrating decreased TB-specific IFN-γ and TNF and increased IL-4 production by CD4+ T cells (Wilcoxon signed-rank p < 0.05). In S. haematobium-infected individuals, these DNA methylation and immune phenotypic changes persisted at least 6 mo after successful deworming. This work demonstrates that helminth infection induces DNA methylation and immune perturbations that inhibit TB-specific immune control and that the duration of these changes are helminth specific.

Optogenetic interrogation reveals separable G-protein-dependent and -independent signalling linking G-protein-coupled receptors to the circadian oscillator

BACKGROUND

Endogenous circadian oscillators distributed across the mammalian body are synchronised among themselves and with external time via a variety of signalling molecules, some of which interact with G-protein-coupled receptors (GPCRs). GPCRs can regulate cell physiology via pathways originating with heterotrimeric G-proteins or β-arrestins. We applied an optogenetic approach to determine the contribution of these two signalling modes on circadian phase.

RESULTS

We employed a photopigment (JellyOp) that activates Gαs signalling with better selectivity and higher sensitivity than available alternatives, and a point mutant of this pigment (F112A) biased towards β-arrestin signalling. When expressed in fibroblasts, both native JellyOp and the F112A arrestin-biased mutant drove light-dependent phase resetting in the circadian clock. Shifts induced by the two opsins differed in their circadian phase dependence and the degree to which they were associated with clock gene induction.

CONCLUSIONS

Our data imply separable G-protein and arrestin inputs to the mammalian circadian clock and establish a pair of optogenetic tools suitable for manipulating Gαs- and β-arrestin-biased signalling in live cells.