Sialic acids (Sias) are abundant terminal modifications of protein-linked glycans. A unique feature of Sia, compared with other monosaccharides, is the formation of linear homo-polymers, with its most complex form polysialic acid (polySia). Sia and polySia mediate diverse biological functions and have great potential for therapeutic use. However, technological hurdles in producing defined protein sialylation due to the enormous structural diversity render their precise investigation a challenge. Here, we describe a plant-based expression platform that enables the controlled in vivo synthesis of sialylated structures with different interlinkages and degree of polymerization (DP). The approach relies on a combination of stably transformed plants with transient expression modules. By the introduction of multigene vectors carrying the human sialylation pathway into glycosylation-destructed mutants, transgenic plants that sialylate glycoproteins in α2,6- or α2,3-linkage were generated. Moreover, by the transient coexpression of human α2,8-polysialyltransferases, polySia structures with a DP >40 were synthesized in these plants. Importantly, plant-derived polySia are functionally active, as demonstrated by a cell-based cytotoxicity assay and inhibition of microglia activation. This pathway engineering approach enables experimental investigations of defined sialylation and facilitates a rational design of glycan structures with optimized biotechnological functions.

Mutations in the gene coding for the integral membrane protein polycystin-1 (PC1) are the cause of most cases of autosomal-dominant polycystic kidney disease (ADPKD), a very common disease that leads to kidney failure and currently lacks approved treatment. Recent work has revealed that PC1 can regulate the transcription factor STAT3, and that STAT3 is aberrantly activated in the kidneys of ADPKD patients and PKD mouse models. Recent approaches to directly inhibit STAT3 in PKD mouse models have been promising. Numerous signaling pathways are known to activate STAT3 and many have long been implicated in the pathogenesis of PKD-such as EGF/EGFR, HGF/c-Met, Src. However, a role of STAT3 in the pathogenesis of PKD had never been considered until now. Here, we review the current findings that suggest that STAT3 is a promising target for the treatment of PKD. Polycystic Kidney Disease ADPKD is a very common life-threatening, monogenic disease that is characterized by excessive proliferation and the growth of epithelial-lined cysts that eventually destroy the normal renal parenchyma [1, 2]. Most patients eventually progress to renal failure and will require dialysis or kidney transplantation. No approved treatment is currently available to halt or slow disease progression. However, a recent phase 3 trial using a vasopressin V 2receptor antagonist has shown promise in slowing the decline in kidney function [3]. ADPKD is caused by mutations in the PKD1 or PKD2 genes which encode the proteins polycystin-1 (PC1) and polycystin-2 (PC2), respectively. PC2 is a calcium channel of the TRP family, and forms a complex with PC1. In addition, PC1-which is mutated in most cases of ADPKD-has been shown to interact with a wide variety of signaling proteins and regulates numerous signaling pathways including heterotrimeric G proteins, wnt-, integrinand JAK/STAT-signaling, and the mTOR pathway. It has remained unclear which of these 1

Background Our laboratory published the first evidence that nutritional ketosis, induced by ketogenic diet (KD) or time-restricted diet (TRD), ameliorates disease progression in PKD animal models. We reasoned that, due to their frequent use for numerous health benefits, some ADPKD patients may already have had experience with ketogenic dietary interventions (KDIs). This retrospective case series study is designed to collect first real-life observations of ADPKD patients about safety, feasibility, and possible benefits of KDIs in ADPKD as part of a translational project pipeline. Methods Patients with ADPKD who had already used KDIs were recruited to retrospectively collect observational and medical data about beneficial or adverse effects, the feasibility and safety of KDIs in questionnaire-based interviews. Results 131 ADPKD patients took part in this study. 74 executed a KD and 52 TRD, for 6 months on average. 86% of participants reported that KDIs had improved their overall health. 67% described improvements in ADPKD-associated health issues. 90% observed significant weight loss. 64% of participants with hypertension reported improvements in blood pressure. 66% noticed adverse effects that are frequently observed with KDIs. 22 participants reported safety concerns like hyperlipidemia. 45 participants reported slight improvements in eGFR. 92% experienced KDIs as feasible while 53% reported breaks during their diet. Discussion Our preliminary data indicate that KDIs may be safe, feasible, and potentially beneficial for ADPKD patients highlighting that prospective clinical trials are warranted to confirm these results in a controlled setting and elucidate the impact of KDIs specifically on kidney function and cyst progression.

BackgroundSialic acids represent common terminal residues on numerous mammalian glycoconjugates, thereby influencing e.g. lumen formation in developing blood vessels. Interestingly, besides monosialylated also polysialylated glycoconjugates are produced by endothelial cells. Polysialic acid (polySia) is formed in several organs during embryonal and postnatal development influencing, for instance, cell migration processes. Furthermore, the function of cytokines like basic fibroblast growth factor (bFGF) is modulated by polySia.ResultsIn this study, we demonstrated that human umbilical vein endothelial cells (HUVEC) also secrete polysialylated glycoconjugates. Furthermore, an interaction between polySia and vascular endothelial growth factor (VEGF) was observed. VEGF modulates like bFGF the migration of HUVEC. Since both growth factors interact with polySia, we examined, if polySia modulates the migration of HUVEC. To this end scratch assays were performed showing that the migration of HUVEC is stimulated, when polySia was degraded.ConclusionsSince polySia can interact with bFGF as well as VEGF and the degradation of polySia resulted in an increased cell migration capacity in the applied scratch assay, we propose that polySia may trap these growth factors influencing their biological activity. Thus, polySia might also contribute to the fine regulation of physiological processes in endothelial cells.