MFSD12 depletion reduces cystine accumulation without improvement in proximal tubular function in experimental models for cystinosis.

Cystinosis is an autosomal recessive lysosomal storage disorder, caused by mutations in the CTNS gene, resulting in an absent or altered cystinosin (CTNS) protein. Cystinosin exports cystine out of the lysosome, with a malfunction resulting in cystine accumulation and a defect in other cystinosin-mediated pathways. Cystinosis is a systemic disease, but the kidneys are the first and most severely affected organs. In the kidney, the disease initially manifests as a generalized dysfunction in the proximal tubules (also called renal Fanconi syndrome). MFSD12 is a lysosomal cysteine importer that directly affects the cystine levels in melanoma cells, HEK293T cells, and cystinosis patient-derived fibroblasts. In this study, we aimed to evaluate MFSD12 mRNA levels in cystinosis patient-derived proximal tubular epithelial cells (ciPTECs) and to study the effect of MFSD12 knockout on cystine levels. We showed similar MFSD12 mRNA expression in patient-derived ciPTECs in comparison with the control cells. CRISPR MFSD12 knockout in a patient-derived ciPTEC (CTNSΔ57kb) resulted in significantly reduced cystine levels. Furthermore, we evaluated proximal tubular reabsorption after injection of mfsd12a translation-blocking morpholino (TB MO) in a ctns-/- zebrafish model. This resulted in decreased cystine levels but caused a concentration-dependent increase in embryo dysmorphism. Furthermore, the mfsd12a TB MO injection did not improve proximal tubular reabsorption or megalin expression. In conclusion, MFSD12 mRNA depletion reduced cystine levels in both tested models without improvement of the proximal tubular function in the ctns-/- zebrafish embryo. In addition, the apparent toxicity of higher mfsd12a TB MO concentrations on the zebrafish development warrants further evaluation.NEW & NOTEWORTHY In this study, we show that MFSD12 depletion with either CRISPR/Cas9-mediated gene editing or a translation-blocking morpholino significantly reduced cystine levels in cystinosis ciPTECs and ctns-/- zebrafish embryos, respectively. However, we observed no improvement in the proximal tubular reabsorption of dextran in the ctns-/- zebrafish embryos injected with mfsd12a translation-blocking morpholino. Furthermore, a negative effect of the mfsd12a morpholino on the zebrafish development warrants further investigation.

Exploiting the aggregation propensity of beta-lactamases to design inhibitors that induce enzyme misfolding.

There is an arms race between beta-lactam antibiotics development and co-evolving beta-lactamases, which provide resistance by breaking down beta-lactam rings. We have observed that certain beta-lactamases tend to aggregate, which persists throughout their evolution under the selective pressure of antibiotics on their active sites. Interestingly, we find that existing beta-lactamase active site inhibitors can act as molecular chaperones, promoting the proper folding of these resistance factors. Therefore, we have created Pept-Ins, synthetic peptides designed to exploit the structural weaknesses of beta-lactamases by causing them to misfold into intracellular inclusion bodies. This approach restores sensitivity to a wide range of beta-lactam antibiotics in resistant clinical isolates, including those with Extended Spectrum variants that pose significant challenges in medical practice. Our findings suggest that targeted aggregation of resistance factors could offer a strategy for identifying molecules that aid in addressing the global antibiotic resistance crisis.

Sequence-targeted Peptides Divert Functional Bacterial Amyloid Towards Destabilized Aggregates and Reduce Biofilm Formation.

Functional bacterial amyloid provides structural stability in biofilm, making it a promising target for anti-biofilm therapeutics. Fibrils formed by CsgA, the major amyloid component in E. coli are extremely robust and can withstand very harsh conditions. Like other functional amyloids, CsgA contains relatively short aggregation-prone regions (APR) which drive amyloid formation. Here, we demonstrate the use of aggregation-modulating peptides to knock down CsgA protein into aggregates with low stability and altered morphology. Remarkably, these CsgA-peptides also modulate fibrillation of the unrelated functional amyloid protein FapC from Pseudomonas, possibly through recognition of FapC segments with structural and sequence similarity with CsgA. The peptides also reduce the level of biofilm formation in E. coli and P. aeruginosa, demonstrating the potential for selective amyloid targeting to combat bacterial biofilm.

Enhanced therapeutic window for antimicrobial Pept-ins by investigating their structure-activity relationship.

The overconsumption and inappropriate use of antibiotics is escalating antibiotic resistance development, which is now one of the 10 top threats to global health. Introducing antibiotics with a novel mode of action into clinical use is urgently needed to address this issue. Deliberately inducing aggregation of target proteins and disrupting protein homeostasis in bacteria via amyloidogenic peptides, also called Pept-ins (from peptide interferors), can be lethal to bacteria and shows considerable promise as a novel antibiotic strategy. However, the translation of Pept-ins into the clinic requires further investigation into their mechanism of action and improvement of their therapeutic window. Therefore, we performed systematic structure modifications of 2 previously discovered Pept-ins, resulting in 179 derivatives, and investigated the corresponding impact on antimicrobial potency, cellular accumulation, and ability to induce protein aggregation in bacteria, in vitro aggregation property, and toxicity on mammalian cells. Our results show that both Pept-in accumulation and aggregation of target proteins in bacteria are requisite for Pept-in mediated antimicrobial activity. Improvement of these two parameters can be achieved via increasing the number of arginine residues, increasing Pept-in aggregation propensity, optimizing the aggregate core structure, adopting ß-turn linkers, or forming a disulphide bond. Correspondingly, improvement of these two parameters can enhance Pept-in antimicrobial efficacy against wildtype E. coli BL21 used in the laboratory as well as clinically isolated multidrug-resistant strain E. coli ATCC, A. baumannii, and K. pneumoniae.

Exploiting the intrinsic misfolding propensity of the KRAS oncoprotein.

Mutant KRAS is a major driver of oncogenesis in a multitude of cancers but remains a challenging target for classical small molecule drugs, motivating the exploration of alternative approaches. Here, we show that aggregation-prone regions (APRs) in the primary sequence of the oncoprotein constitute intrinsic vulnerabilities that can be exploited to misfold KRAS into protein aggregates. Conveniently, this propensity that is present in wild-type KRAS is increased in the common oncogenic mutations at positions 12 and 13. We show that synthetic peptides (Pept-ins™) derived from two distinct KRAS APRs could induce the misfolding and subsequent loss of function of oncogenic KRAS, both of recombinantly produced protein in solution, during cell-free translation and in cancer cells. The Pept-ins exerted antiproliferative activity against a range of mutant KRAS cell lines and abrogated tumor growth in a syngeneic lung adenocarcinoma mouse model driven by mutant KRAS G12V. These findings provide proof-of-concept that the intrinsic misfolding propensity of the KRAS oncoprotein can be exploited to cause its functional inactivation.

Synthetic Pept-Ins as a Generic Amyloid-Like Aggregation-Based Platform for In Vivo PET Imaging of Intracellular Targets.

Amyloid-like aggregation of proteins is induced by short amyloidogenic sequence segments within a specific protein sequence resulting in self-assembly into ß-sheets. We recently validated a technology platform in which synthetic amyloid peptides ("Pept-ins") containing a specific aggregation-prone region (APR) are used to induce specific functional knockdown of the target protein from which the APR was derived, including bacterial, viral, and mammalian cell proteins. In this work, we investigated if Pept-ins can be used as vector probes for in vivo Positron Emission Tomography (PET) imaging of intracellular targets. The radiolabeled Pept-ins [68Ga]Ga-NODAGA-PEG4-vascin (targeting VEGFR2) and [68Ga]Ga-NODAGA-PEG2-P2 (targeting E. coli) were evaluated as PET probes. The Pept-in based radiotracers were cross-validated in a murine tumor and muscle infection model, respectively, and were found to combine target specificity with favorable in vivo pharmacokinetics. When the amyloidogenicity of the interacting region of the peptide is suppressed by mutation, cellular uptake and in vivo accumulation are abolished, highlighting the importance of the specific design of synthetic Pept-ins. The ubiquity of target-specific amyloidogenic sequence segments in natural proteins, the straightforward sequence-based design of the Pept-in probes, and their spontaneous internalization by cells suggest that Pept-ins may constitute a generic platform for in vivo PET imaging of intracellular targets.

The Dynamic Transition of Persistence toward the Viable but Nonculturable State during Stationary Phase Is Driven by Protein Aggregation.

Decades of research into bacterial persistence has been unable to fully characterize this antibiotic-tolerant phenotype, thereby hampering the development of therapies effective against chronic infections. Although some active persister mechanisms have been identified, the prevailing view is that cells become persistent because they enter a dormant state. We therefore characterized starvation-induced dormancy in Escherichia coli. Our findings indicate that dormancy develops gradually; persistence strongly increases during stationary phase and decreases again as persisters enter the viable but nonculturable (VBNC) state. Importantly, we show that dormancy development is tightly associated with progressive protein aggregation, which occurs concomitantly with ATP depletion during starvation. Persisters contain protein aggregates in an early developmental stage, while VBNC cells carry more mature aggregates. Finally, we show that at least one persister protein, ObgE, works by triggering aggregation, even at endogenous levels, and thereby changing the dynamics of persistence and dormancy development. These findings provide evidence for a genetically controlled, gradual development of persisters and VBNC cells through protein aggregation. IMPORTANCE While persistence and the viable but nonculturable (VBNC) state are currently investigated in isolation, our results strongly indicate that these phenotypes represent different stages of the same dormancy program and that they should therefore be studied within the same conceptual framework. Moreover, we show here for the first time that the dynamics of protein aggregation perfectly match the onset and further development of bacterial dormancy and that different dormant phenotypes are linked to different stages of protein aggregation. Our results thereby strongly hint at a causal relationship between both. Because many conditions known to trigger persistence are also known to influence aggregation, it is tempting to speculate that a variety of different persister pathways converge at the level of protein aggregation. If so, aggregation could emerge as a general principle that underlies the development of persistence which could be exploited for the design of antipersister therapies.

Gene Erosion Can Lead to Gain-of-Function Alleles That Contribute to Bacterial Fitness.

Despite our extensive knowledge of the genetic regulation of heat shock proteins (HSPs), the evolutionary routes that allow bacteria to adaptively tune their HSP levels and corresponding proteostatic robustness have been explored less. In this report, directed evolution experiments using the Escherichia coli model system unexpectedly revealed that seemingly random single mutations in its tnaA gene can confer significant heat resistance. Closer examination, however, indicated that these mutations create folding-deficient and aggregation-prone TnaA variants that in turn can endogenously and preemptively trigger HSP expression to cause heat resistance. These findings, importantly, demonstrate that even erosive mutations with disruptive effects on protein structure and functionality can still yield true gain-of-function alleles with a selective advantage in adaptive evolution.

Bacterial Protein Homeostasis Disruption as a Therapeutic Intervention.

Cells have evolved a complex molecular network, collectively called the protein homeostasis (proteostasis) network, to produce and maintain proteins in the appropriate conformation, concentration and subcellular localization. Loss of proteostasis leads to a reduction in cell viability, which occurs to some degree during healthy ageing, but is also the root cause of a group of diverse human pathologies. The accumulation of proteins in aberrant conformations and their aggregation into specific beta-rich assemblies are particularly detrimental to cell viability and challenging to the protein homeostasis network. This is especially true for bacteria; it can be argued that the need to adapt to their changing environments and their high protein turnover rates render bacteria particularly vulnerable to the disruption of protein homeostasis in general, as well as protein misfolding and aggregation. Targeting bacterial proteostasis could therefore be an attractive strategy for the development of novel antibacterial therapeutics. This review highlights advances with an antibacterial strategy that is based on deliberately inducing aggregation of target proteins in bacterial cells aiming to induce a lethal collapse of protein homeostasis. The approach exploits the intrinsic aggregation propensity of regions residing in the hydrophobic core regions of the polypeptide sequence of proteins, which are genetically conserved because of their essential role in protein folding and stability. Moreover, the molecules were designed to target multiple proteins, to slow down the build-up of resistance. Although more research is required, results thus far allow the hope that this strategy may one day contribute to the arsenal to combat multidrug-resistant bacterial infections.

Investigating the mechanism of action of aggregation-inducing antimicrobial Pept-ins.

Aggregation can be selectively induced by aggregation-prone regions (APRs) contained in the target proteins. Aggregation-inducing antimicrobial peptides (Pept-ins) contain sequences homologous to APRs of target proteins and exert their bactericidal effect by causing aggregation of a large number of proteins. To better understand the mechanism of action of Pept-ins and the resistance mechanisms, we analyzed the phenotypic, lipidomic, and transcriptomic as well as genotypic changes in laboratory-derived Pept-in-resistant E. coli mutator cells. The analysis showed that the Pept-in resistance mechanism is dominated by a decreased Pept-in uptake, in both laboratory-derived mutator cells and clinical isolates. Our data indicate that Pept-in uptake involves an electrostatic attraction between the Pept-in and the bacterial membrane and follows a complex mechanism potentially involving many transporters. Furthermore, it seems more challenging for bacteria to become resistant toward Pept-ins that are less dependent on electrostatic attraction for uptake, suggesting that future Pept-ins should be selected for this property.

Reverse engineering synthetic antiviral amyloids.

Human amyloids have been shown to interact with viruses and interfere with viral replication. Based on this observation, we employed a synthetic biology approach in which we engineered virus-specific amyloids against influenza A and Zika proteins. Each amyloid shares a homologous aggregation-prone fragment with a specific viral target protein. For influenza we demonstrate that a designer amyloid against PB2 accumulates in influenza A-infected tissue in vivo. Moreover, this amyloid acts specifically against influenza A and its common PB2 polymorphisms, but not influenza B, which lacks the homologous fragment. Our model amyloid demonstrates that the sequence specificity of amyloid interactions has the capacity to tune amyloid-virus interactions while allowing for the flexibility to maintain activity on evolutionary diverging variants.

Development of antiseptic adaptation and cross-adapatation in selected oral pathogens in vitro.

There is evidence that pathogenic bacteria can adapt to antiseptics upon repeated exposure. More alarming is the concomitant increase in antibiotic resistance that has been described for some pathogens. Unfortunately, effects of adaptation and cross-adaptation are hardly known for oral pathogens, which are very frequently exposed to antiseptics. Therefore, this study aimed to determine the in vitro increase in minimum inhibitory concentrations (MICs) in oral pathogens after repeated exposure to chlorhexidine or cetylpyridinium chloride, to examine if (cross-)adaptation to antiseptics/antibiotics occurs, if (cross-)adaptation is reversible and what the potential underlying mechanisms are. When the pathogens were exposed to antiseptics, their MICs significantly increased. This increase was in general at least partially conserved after regrowth without antiseptics. Some of the adapted species also showed cross-adaptation, as shown by increased MICs of antibiotics and the other antiseptic. In most antiseptic-adapted bacteria, cell-surface hydrophobicity was increased and mass-spectrometry analysis revealed changes in expression of proteins involved in a wide range of functional domains. These in vitro data shows the adaptation and cross-adaptation of oral pathogens to antiseptics and antibiotics. This was related to changes in cell surface hydrophobicity and in expression of proteins involved in membrane transport, virulence, oxidative stress protection and metabolism.

Ses proteins as possible targets for vaccine development against Staphylococcus epidermidis infections.

OBJECTIVES: The opportunistic pathogen Staphylococcus epidermidis is progressively involved in device-related infections. Since these infections involve biofilm formation, antibiotics are not effective. Conversely, a vaccine can be advantageous to prevent these infections. In view of vaccine development, predicted surface proteins were evaluated on their potential as a vaccine target. METHODS: Immunoglobulins directed against S. epidermidis surface proteins SesB, M, O, Q and R were used to firstly affirm their surface location. Further, inhibitory effects of these IgGs on biofilm formation were determined in vitro on polystyrene and polyurethane surfaces and in vivo using a subcutaneous catheter mouse model. We also examined the opsonophagocytotic capacity of these IgGs. RESULTS: Surface localization of the five Ses proteins was demonstrated both for planktonic and sessile cells, though to a variable extent. Ses-specific IgGs added to planktonic cells had a variable inhibitory effect on cell adhesion to polystyrene, while only anti-SesO IgGs decreased cell attachment to polyurethane catheters. Although phagocytic killing was only obtained after opsonization with SesB-specific IgGs, a significant reduction of in vivo formed biofilms was observed after administration of SesB-, SesM- and SesO-specific IgGs. CONCLUSIONS: Regardless of their characterization or function, S. epidermidis surface proteins can be adequate targets for vaccine development aiming the prevention of device-related infections caused by invasive S. epidermidis strains.

Aggregating sequences that occur in many proteins constitute weak spots of bacterial proteostasis.

Aggregation is a sequence-specific process, nucleated by short aggregation-prone regions (APRs) that can be exploited to induce aggregation of proteins containing the same APR. Here, we find that most APRs are unique within a proteome, but that a small minority of APRs occur in many proteins. When aggregation is nucleated in bacteria by such frequently occurring APRs, it leads to massive and lethal inclusion body formation containing a large number of proteins. Buildup of bacterial resistance against these peptides is slow. In addition, the approach is effective against drug-resistant clinical isolates of Escherichia coli and Acinetobacter baumannii, reducing bacterial load in a murine bladder infection model. Our results indicate that redundant APRs are weak points of bacterial protein homeostasis and that targeting these may be an attractive antibacterial strategy.

Pituitary adenylate cyclase-activating polypeptide (PACAP) in zebrafish models of nephrotic syndrome.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an inhibitor of megakaryopoiesis and platelet function. Recently, PACAP deficiency was observed in children with nephrotic syndrome (NS), associated with increased platelet count and aggregability and increased risk of thrombosis. To further study PACAP deficiency in NS, we used transgenic Tg(cd41:EGFP) zebrafish with GFP-labeled thrombocytes. We generated two models for congenital NS, a morpholino injected model targeting nphs1 (nephrin), which is mutated in the Finnish-type congenital NS. The second model was induced by exposure to the nephrotoxic compound adriamycin. Nephrin RNA expression was quantified and zebrafish embryos were live-screened for proteinuria and pericardial edema as evidence of renal impairment. Protein levels of PACAP and its binding-protein ceruloplasmin were measured and GFP-labeled thrombocytes were quantified. We also evaluated the effects of PACAP morpholino injection and the rescue effects of PACAP-38 peptide in both congenital NS models. Nephrin downregulation and pericardial edema were observed in both nephrin morpholino injected and adriamycin exposed congenital NS models. However, PACAP deficiency was demonstrated only in the adriamycin exposed condition. Ceruloplasmin levels and the number of GFP-labeled thrombocytes remained unchanged in both models. PACAP morpholino injections worsened survival rates and the edema phenotype in both congenital NS models while injection with human PACAP-38 could only rescue the adriamycin exposed model. We hereby report, for the first time, PACAP deficiency in a NS zebrafish model as a consequence of adriamycin exposure. However, distinct from the human congenital NS, both zebrafish models retained normal levels of ceruloplasmin and thrombocytes. We further extend the renoprotective effects of the PACAP-38 peptide against adriamycin toxicity in zebrafish.

Cystinosis (ctns) zebrafish mutant shows pronephric glomerular and tubular dysfunction.

The human ubiquitous protein cystinosin is responsible for transporting the disulphide amino acid cystine from the lysosomal compartment into the cytosol. In humans, Pathogenic mutations of CTNS lead to defective cystinosin function, intralysosomal cystine accumulation and the development of cystinosis. Kidneys are initially affected with generalized proximal tubular dysfunction (renal Fanconi syndrome), then the disease rapidly affects glomeruli and progresses towards end stage renal failure and multiple organ dysfunction. Animal models of cystinosis are limited, with only a Ctns knockout mouse reported, showing cystine accumulation and late signs of tubular dysfunction but lacking the glomerular phenotype. We established and characterized a mutant zebrafish model with a homozygous nonsense mutation (c.706 C > T; p.Q236X) in exon 8 of ctns. Cystinotic mutant larvae showed cystine accumulation, delayed development, and signs of pronephric glomerular and tubular dysfunction mimicking the early phenotype of human cystinotic patients. Furthermore, cystinotic larvae showed a significantly increased rate of apoptosis that could be ameliorated with cysteamine, the human cystine depleting therapy. Our data demonstrate that, ctns gene is essential for zebrafish pronephric podocyte and proximal tubular function and that the ctns-mutant can be used for studying the disease pathogenic mechanisms and for testing novel therapies for cystinosis.

De novo design of a biologically active amyloid.

Most human proteins possess amyloidogenic segments, but only about 30 are associated with amyloid-associated pathologies, and it remains unclear what determines amyloid toxicity. We designed vascin, a synthetic amyloid peptide, based on an amyloidogenic fragment of vascular endothelial growth factor receptor 2 (VEGFR2), a protein that is not associated to amyloidosis. Vascin recapitulates key biophysical and biochemical characteristics of natural amyloids, penetrates cells, and seeds the aggregation of VEGFR2 through direct interaction. We found that amyloid toxicity is observed only in cells that both express VEGFR2 and are dependent on VEGFR2 activity for survival. Thus, amyloid toxicity here appears to be both protein-specific and conditional-determined by VEGFR2 loss of function in a biological context in which target protein function is essential.

sesC as a genetic marker for easy identification of Staphylococcus epidermidis from other isolates.

Staphylococcus epidermidis is one of the major concerns with respect to hospital-acquired infections. Therefore, a rapid and easy method to identify at species level S. epidermidis isolates out of a broad range of bacteria is necessary. Based on earlier studies, the sesC gene encoding a S. epidermidis surface protein revealed to be a highly conserved gene in this species. By means of an easy and inexpensive PCR assay, the presence of sesC was checked in 438 clinical staphylococcal isolates. Results showed that sesC is specifically present in all S. epidermidis. In conclusion, the sesC gene can be exploited as a genetic marker in order to distinguish S. epidermidis from other isolates.