Julien Dairou

Background/Purpose: Phototoxicity is a common adverse effect triggered by systemic or topical drug treatments. It is mainly caused by drug‐induced sensitization to UVA radiation, arising from either the drug's inherent photosensitizing potential or its interference with the metabolism of endogenous photosensitizers. A potent endogenous UVA sensitizer is 6‐formylindolo[3,2‐ b ]carbazole (FICZ), a tryptophan photoproduct formed in UVB‐irradiated epidermal cells. By sequentially activating the aryl hydrocarbon receptor signaling pathway and inducing cytochrome P450 (CYP) 1A1 expression, FICZ induces its own degradation. Recently, we reported that the BRAF inhibitor vemurafenib interferes with CYP1A1 activity and sensitizes keratinocytes to FICZ/UVA‐induced phototoxicity. Herein, we screened 12 clinical drugs, known to exhibit phototoxicity in patients, for their potential to interfere with the metabolism of (exogenous) FICZ and sensitize HaCaT keratinocytes to UVA‐induced phototoxicity. Methods: The UV–VIS absorption of the drugs was determined, and their effect on CYP1A1 activity and FICZ/UVA‐triggered apoptosis was assessed in immortalized and primary human keratinocytes using 7‐ethoxyresorufin‐O‐deethylase (EROD) and caspase‐3 activity assays. Moreover, the impact of the candidate drugs on the metabolic degradation of FICZ in cells (LC analysis) as well as on the generation of oxidative stress (MitoSOX assay, qPCR analyses) was investigated. Results: We identified two drugs, erlotinib and leflunomide, to sensitize human keratinocytes to FICZ/UVA‐induced apoptosis by inhibiting CYP1A1 activity. Moreover, both drugs attenuated the metabolic breakdown of FICZ, enhanced the FICZ/UVA‐triggered formation of mitochondrial superoxide anions, and increased heme oxygenase‐1 (HMOX1) transcript levels, indicative of antioxidant defense activation. Conclusion: Disruption of FICZ metabolism may contribute to the phototoxicity of drugs.

Leucettinibs are substituted 2-aminoimidazolin-4-ones inspired by the marine sponge natural product Leucettamine B and developed as pharmacological inhibitors of DYRK1A (dual-specificity, tyrosine phosphorylation-regulated kinase 1A), a therapeutic target for indications such as Down syndrome, Alzheimer’s disease, Parkinson’s disease, diabetes, myocardial infarction, etc. Leucettinib-21 is currently being tested in a phase 1 clinical trial. In this study, four different affinity chromatography-based approaches were developed to identify the rat brain targets of Leucettinib-21: (1) Leucettinib-21 (and its kinase-inactive isomer as control) immobilized on agarose beads, (2) immobilized metal affinity chromatography, (3) KinAffinity bead competition assays, and (4) immunoprecipitation with DYRK1A-specific antibodies. Altogether, these complementary methods (1) confirm known targets of Leucettinib-21, and identify (2) new protein kinases and nonkinases interacting with Leucettinib-21, (3) potential new partners of DYRK1A, and (4) pathways and cellular mechanisms potentially modulated by Leucettinib-21. These methods can be expanded to various cells and tissues from models of pathologies where Leucettinib-21 demonstrates efficacy.

Bacterial membranes comprise diverse lipids whose proportions vary according to environmental conditions. How cells direct lipid flux toward specific products remains unclear. We address this question in the human pathogen Staphylococcus aureus, where multiple lipid products compete for a common precursor, the major phospholipid, phosphatidylglycerol (PG). One product, lipoteichoic acid (LTA), is essential for cell division, envelope homeostasis, and virulence. Lipids and metabolites were quantified to identify factors that prioritize LTA synthesis over the other PG-derived products. We identify upstream fatty acid synthesis (FASII) pathway as a key control point for LTA production. Inhibition of FASII by antibiotics or gene inactivation causes LTA depletion. FASII inhibition similarly affects LTA in Streptococcus agalactiae, suggesting conservation of this LTA control strategy. Changes in membrane fatty acids do not account for LTA depletion. Instead, we show that FASII inhibition causes a drop in intracellular glycerophosphate (GroP), a precursor for both PG and LTA. Under these conditions of GroP limitation, PG flux favors production of a non-GroP lipid, cardiolipin. Moreover, combined inhibition of FASII and WTA blocks S. aureus growth, confirming the lethality of depleting LTA and WTA simultaneously. This study resolves how S. aureus manages phospholipid flux, by prioritizing the synthesis of GroP-rich LTA or of non-GroP-containing lipids according to FASII-controlled GroP availability.

Dysregulated expression and activity of DYRK1A, dual specificity tyrosine phosphorylation regulated kinase 1A, is a feature of several neurodevelopmental and neurodegenerative diseases, including Down syndrome, DYRK1A syndrome, autism spectrum disorders, Alzheimer’s disease, and Parkinson’s disease. Thus, manipulating DYRK1A activity in the brain has emerged as a potential therapeutic target for neurological disorders. Several DYRK1A inhibitors have shown promise for improving cognition in rodent models of Down syndrome and Alzheimer’s disease, for example, but the ability to affect DYRK1A levels or activity in relevant human cells has not been established. We filled this gap by testing the effects of a new DYRK1A inhibitor on trisomy 21 induced pluripotent stem cell derived neural progenitor cells and neurons, where DYRK1A expression and activity are increased. Our results demonstrate that Leucettinib-21, a potent and selective low-molecular weight pharmacological inhibitor of DYRK1A, decreases DYRK1A activity in human trisomy 21 neural progenitor cells and cortical neurons. We show for the first time that Leucettinib-21 reduces DYRK1A activity in a relevant human disease model, supporting future human trials. Summary Statement: We show for the first time that Leucettinib-21, a pharmacological inhibitor of DYRK1A, decreases DYRK1A activity in a human iPSC-derived neural cell culture model of Down syndrome.

The protein DJ-1 appears to play a protective role in the development of Parkinson's disease (PD). Here, we show that endogenous neurotoxins of the 1,2,3,4-tetrahydroisoquinoline family (TIQs), formed upon reaction of various aldehydes such as methylglyoxal (MGO) with the neurotransmitter dopamine, act as irreversible inhibitors of the esterase activity of human DJ-1, with IC50 values between 15 and 57 μM. The presence of a catechol function appears to be essential for these inhibitory effects, which may be at the origin of the oxidation of cysteine 106, a crucial residue in the DJ-1 active site, thereby leading to DJ-1 inhibition. We also show that these endogenous neurotoxins inhibit the protective effects of DJ-1 against glycated guanosine diphosphate (GDP) formation and against alpha-synuclein (aSyn) aggregation induced by MGO. In total, the observed inhibition of DJ-1 by these endogenous neurotoxins may contribute to their damaging effects on the nervous system and, should be taken into account in therapeutic strategies for PD and related disorders.

Proliferative glomerulonephritis is a severe condition that often leads to kidney failure. There is a significant lack of effective treatment for these disorders. Here, following the identification of a somatic PIK3CA gain-of-function mutation in podocytes of a patient, we demonstrate using multiple genetically engineered mouse models, single-cell RNA sequencing, and spatial transcriptomics the crucial role played by this pathway for proliferative glomerulonephritis development by promoting podocyte proliferation, dedifferentiation, and inflammation. Additionally, we show that alpelisib, a PI3Kα inhibitor, improves glomerular lesions and kidney function in different mouse models of proliferative glomerulonephritis and lupus nephritis by targeting podocytes. Surprisingly, we determined that pharmacological inhibition of PI3Kα affects B and T lymphocyte populations in lupus nephritis mouse models, with a decrease in the production of proinflammatory cytokines, autoantibodies, and glomerular complement deposition, which are all characteristic features of PI3Kδ inhibition, the primary PI3K isoform expressed in lymphocytes. Importantly, PI3Kα inhibition does not impact lymphocyte function under normal conditions. These findings were then confirmed in human lymphocytes isolated from patients with active lupus nephritis. In conclusion, we demonstrate the major role played by PI3Kα in proliferative glomerulonephritis and show that in this condition, alpelisib acts on both podocytes and the immune system.

Summary: Lysosomal degradation of macromolecules in lysosomes produces diverse small metabolites exported by specific transporters for reuse in biosynthetic pathways. Here, we deorphanized the Major Facilitator Superfamily Domain Containing 1 (MFSD1) protein, which forms a tight complex with the Glycosylated Lysosomal Membrane Protein (GLMP) in the lysosomal membrane. Untargeted metabolomics analysis of MFSD1-deficient mouse lysosomes revealed an increase in cationic dipeptides. Purified MFSD1 selectively bound diverse dipeptides, while electrophysiological, isotope tracer, and fluorescence-based studies in Xenopus oocytes and proteoliposomes showed that MFSD1/GLMP acts as a uniporter for cationic and neutral dipeptides. Cryo-EM structure of the dipeptide-bound MFSD1/GLMP complex in outward-open conformation characterized the heterodimer interface and, in combination with molecular dynamics simulations, provided a structural basis for its selectivity towards diverse dipeptides. Together, our data identify MFSD1 as a general lysosomal dipeptide uniporter, providing an alternative route to recycle lysosomal proteolysis products when lysosomal amino acid exporters are overloaded.