Endocrine regulation of MFS2 by branchless controls phosphate excretion and stone formation in Drosophila renal tubules

Mechanistic characterization of a Drosophila model of paraneoplastic nephrotic syndrome

Paraneoplastic syndromes occur in cancer patients and originate from dysfunction of organs at a distance from the tumor or its metastasis. A wide range of organs can be affected in paraneoplastic syndromes; however, the pathological mechanisms by which tumors influence host organs are poorly understood. Recent studies in the fly uncovered that tumor secreted factors target host organs, leading to pathological effects. In this study, using a Drosophila gut tumor model, we characterize a mechanism of tumor-induced kidney dysfunction. Specifically, we find that Pvf1, a PDGF/VEGF signaling ligand, secreted by gut tumors activates the PvR/JNK/Jra signaling pathway in the principal cells of the kidney, leading to mis-expression of renal genes and paraneoplastic renal syndrome-like phenotypes. Our study describes an important mechanism by which gut tumors perturb the function of the kidney, which might be of clinical relevance for the treatment of paraneoplastic syndromes.

Upcycling of recycled minerals from sewage sludge through black soldier fly larvae (Hermetia illucens): Impact on growth and mineral accumulation

Phosphorous (P) resources are finite. Sewage sludge recyclates (SSR) are not only of interest as plant fertilizer but also as potential source of minerals in animal nutrition. However, besides P and calcium (Ca), SSR contain heavy metals. Under EU legislation, the use of SSR derivatives in animal feed is not permitted, but given the need to improve nutrient recycling, it could be an environmentally sound future mineral source. Black soldier fly larvae (BSFL) convert low-grade biomass into valuable proteins and lipids, and accumulate minerals in their body. It was hypothesized that BSFL modify and increase their mineral content in response to feeding on SSR containing substrates. The objective was to evaluate the upcycling of minerals from SSR into agri-food nutrient cycles through BSFL. Growth, nutrient and mineral composition were compared in BSFL reared either on a modified Gainesville fly diet (FD) or on FD supplemented with either 4% of biochar (FD + BCH) or 3.6% of single-superphosphate (FD + SSP) recyclate (n = 6 BSFL rearing units/group). Larval mass, mineral and nutrient concentrations and yields were determined, and the bioaccumulation factor (BAF) was calculated. The FD + SSP substrate decreased specific growth rate and crude fat of BSFL (P < 0.05) compared to FD. The FD + SSP larvae had higher Ca and P contents and yields but the BAF for Ca was lowest. The FD + BCH larvae increased Ca, iron, cadmium and lead contents compared to FD. Larvae produced on FD + SSP showed lower lead and higher arsenic concentration than on FD + BCH. Frass of FD + BCH had higher heavy metal concentration than FD + SSP and FD (P < 0.05). Except for cadmium and manganese, the larval heavy metal concentration was below the legally permitted upper concentrations for feed. In conclusion, the SSR used could enrich BSFL with Ca and P but at the expense of growth. Due to the accumulation of Cd and Mn, BSFL or products thereof can only be a component of farmed animal feed whereas in BSFL frass heavy metal concentrations remained below the upper limit authorized by EU.

Transcriptional and functional motifs defining renal function revealed by single-nucleus RNA sequencing

Recent advances in single-cell sequencing provide a unique opportunity to gain novel insights into the diversity, lineage, and functions of cell types constituting a tissue/organ. Here, we performed a single-nucleus study of the adult Drosophila renal system, consisting of Malpighian tubules and nephrocytes, which shares similarities with the mammalian kidney. We identified 11 distinct clusters representing renal stem cells, stellate cells, regionally specific principal cells, garland nephrocyte cells, and pericardial nephrocytes. Characterization of the transcription factors specific to each cluster identified fruitless (fru) as playing a role in stem cell regeneration and Hepatocyte nuclear factor 4 (Hnf4) in regulating glycogen and triglyceride metabolism. In addition, we identified a number of genes, including Rho guanine nucleotide exchange factor at 64C (RhoGEF64c), Frequenin 2 (Frq2), Prip, and CG1093 that are involved in regulating the unusual star shape of stellate cells. Importantly, the single-nucleus dataset allows visualization of the expression at the organ level of genes involved in ion transport and junctional permeability, providing a systems-level view of the organization and physiological roles of the tubules. Finally, a cross-species analysis allowed us to match the fly kidney cell types to mouse kidney cell types and planarian protonephridia, knowledge that will help the generation of kidney disease models. Altogether, our study provides a comprehensive resource for studying the fly kidney.

The fruit fly kidney stone models and their application in drug development

Kidney stone disease is a global problem affecting about 12% of the world population. Novel treatments to control this disease have a huge demand. Here we argue that the fruit fly, as an emerging kidney stone model, can provide a platform for the discovery of new drugs. The renal system of fruit fly (Malpighian tubules) is similar to the mammalian renal tubules in both function and structure. Different fruit fly models for different types of kidney stones including calcium oxalate (CaOx) stones, xanthine stones, uric acid stone, and calcium phosphate (CaP) stones have been successfully established through dietary or genetic approaches in the last ten years, notably improved our understanding of the formation mechanisms of kidney stone diseases. The fruit fly CaOx stones model, which is mediated by treatment with dietary lithogenic agents, is also one of the most potential models for drug development. Various potential antilithogenic agents have been identified using this model, including new chemical compounds and medicinal plants. The fruit fly kidney stone models also afford opportunities to study the therapeutic mechanism of these drugs in deeper.

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Kidney stone disease is a global problem affecting about 12% of the world population.

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The fruit fly kidney stone models were established via dietary or genetic methods.

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New antilithogenic leads can be identified using fruit fly models.

Updates on ion and water transport by the Malpighian tubule

The Malpighian (renal) tubule is capable of transporting fluid at remarkable rates. This review will focus on recent insights into the mechanisms by which these high rates are achieved and controlled, with particular reference to the tubules of Drosophila melanogaster, in which the combination of physiology and genetics has led to particularly rapid progress. Like many vertebrate epithelia, the Drosophila tubule has specialized cell types, with active cation transport confined to a large, metabolically active principal cell; whereas the smaller intercalated stellate cell controls chloride and water shunts to achieve net fluid secretion. Recently, the genes underlying many of these processes have been identified, functionally validated and localized within the tubule. The imminent arrival of new types of post-genomic data (notably single cell sequencing) will herald an exciting era of new discovery.

Transporters and tubule crystals in the insect Malpighian tubule

The insect renal (Malpighian) tubules are functionally homologous to the mammalian kidney. Accumulating evidence indicates that renal tubule crystals form in a manner similar to mammalian kidney stones. In Drosophila melanogaster, crystals can be induced by diet, toxic substances, or genetic mutations that reflect circumstances influencing or eliciting kidney stones in mammals. Incredibly, many mammalian proteins have distinct homologs in Drosophila, and the function of most homologs have been demonstrated to recapitulate their mammalian and human counterparts. Here, we discuss the present literature establishing Drosophila as a nephrolithiasis model. This insect model may be used to investigate and understand the etiology of kidney stone diseases, especially with regard to calcium oxalate, calcium phosphate and xanthine or urate crystallization.

FGF23 signalling and physiology

Fibroblast growth factor 23 (FGF23) is a phosphotropic hormone that belongs to a subfamily of endocrine FGFs with evolutionarily conserved functions in worms and fruit flies. FAM20C phosphorylates FGF23 post-translationally, targeting it to proteolysis through subtilisin-like proprotein convertase FURIN, resulting in secretion of FGF23 fragments. O-glycosylation of FGF23 through GALNT3 appears to prevent proteolysis, resulting in secretion of biologically active intact FGF23. In the circulation, FGF23 may undergo further processing by plasminogen activators. Crystal structures show that the ectodomain of the cognate FGF23 receptor FGFR1c binds with the ectodomain of the co-receptor alpha-KLOTHO. The KLOTHO-FGFR1c double heterodimer creates a high-affinity binding site for the FGF23 C-terminus. The topology of FGF23 deviates from that of paracrine FGFs, resulting in poor affinity for heparan sulphate, which may explain why FGF23 diffuses freely in the bone matrix to enter the bloodstream following its secretion by cells of osteoblastic lineage. Intact FGF23 signalling by this canonical pathway activates FRS2/RAS/RAF/MEK/ERK1/2. It reduces serum phosphate by inhibiting 1,25-dihydroxyvitamin D synthesis, suppressing intestinal phosphate absorption, and by downregulating the transporters NPT2a and NPT2c, suppressing phosphate reabsorption in the proximal tubules. The physiological role of FGF23 fragments, which may be inhibitory, remains unclear. Pharmacological and genetic activation of canonical FGF23 signalling causes hypophosphatemic disorders, while its inhibition results in hyperphosphatemic disorders. Non-canonical FGF23 signalling through binding and activation of FGFR3/FGFR4/calcineurin/NFAT in an alpha-KLOTHO-independent fashion mainly occurs at extremely elevated circulating FGF23 levels and may contribute to mortality due to cardiovascular disease and left ventricular hypertrophy in chronic kidney disease.

Importance of Dietary Phosphorus for Bone Metabolism and Healthy Aging

Inorganic phosphate (Pi) plays a critical function in many tissues of the body: for example, as part of the hydroxyapatite in the skeleton and as a substrate for ATP synthesis. Pi is the main source of dietary phosphorus. Reduced bioavailability of Pi or excessive losses in the urine causes rickets and osteomalacia. While critical for health in normal amounts, dietary phosphorus is plentiful in the Western diet and is often added to foods as a preservative. This abundance of phosphorus may reduce longevity due to metabolic changes and tissue calcifications. In this review, we examine how dietary phosphorus is absorbed in the gut, current knowledge about Pi sensing, and endocrine regulation of Pi levels. Moreover, we also examine the roles of Pi in different tissues, the consequences of low and high dietary phosphorus in these tissues, and the implications for healthy aging.