A microscopic view on the renal endothelial glycocalyx

Endothelial cells perform key homeostatic functions such as regulating blood flow, permeability, and aiding immune surveillance for pathogens. While endothelial activation serves normal physiological adaptation, maladaptation of these endothelial functions has been identified as an important effector mechanism in the progression of renal disease as well as the associated development of cardiovascular disease. The primary interface between blood and the endothelium is the glycocalyx. This carbohydrate-rich gel-like structure with its associated proteins mediates most of the regulatory functions of the endothelium. Because the endothelial glycocalyx is a highly dynamic and fragile structure ex vivo, and traditional tissue processing for staining and perfusion-fixation usually results in a partial or complete loss of the glycocalyx, studying its dimensions and function has proven to be challenging. In this review, we will outline the core functions of the glycocalyx and focus on different techniques to study structure-function relationships in kidney and vasculature.

Shear Stress Regulation of Endothelial Glycocalyx Structure Is Determined by Glucobiosynthesis

OBJECTIVE

Endothelial cells exposed to laminar shear stress express a thick glycocalyx on their surface that plays an important role in reducing vascular permeability and endothelial anti-inflammatory, antithrombotic, and antiangiogenic properties. Production and maintenance of this glycocalyx layer is dependent on cellular carbohydrate synthesis, but its regulation is still unknown. Approach and Results: Here, we show that biosynthesis of the major structural component of the endothelial glycocalyx, hyaluronan, is regulated by shear. Both in vitro as well as in in vivo, hyaluronan expression on the endothelial surface is increased on laminar shear and reduced when exposed to oscillatory flow, which is regulated by KLF2 (Krüppel-like Factor 2). Using a CRISPR-CAS9 edited small tetracysteine tag to endogenous HAS2 (hyaluronan synthase 2), we demonstrated increased translocation of HAS2 to the endothelial cell membrane during laminar shear. Hyaluronan production by HAS2 was shown to be further driven by availability of the hyaluronan substrates UDP-glucosamine and UDP-glucuronic acid. KLF2 inhibits endothelial glycolysis and allows for glucose intermediates to shuttle into the hexosamine- and glucuronic acid biosynthesis pathways, as measured using nuclear magnetic resonance analysis in combination with ¹³C-labeled glucose.

CONCLUSIONS

These data demonstrate how endothelial glycocalyx function and functional adaptation to shear is coupled to KLF2-mediated regulation of endothelial glycolysis.

Endothelial Glycocalyx Hyaluronan: Regulation and Role in Prevention of Diabetic Complications

The endothelial glycocalyx is critically involved in vascular integrity and homeostasis, by regulating vascular permeability, regulating mechanotransduction, and reducing inflammation and coagulation. The turnover of the glycocalyx is dynamic to fine-tune these processes. This is in particular true for its main structural component, hyaluronan (HA). Degradation and shedding of the glycocalyx by enzymes, such as hyaluronidase 1 and hyaluronidase 2, are responsible for regulation of the glycocalyx thickness and hence access of circulating cells and factors to the endothelial cell membrane and its receptors. This degradation process will at the same time also allow for resynthesis and adaptive chemical modification of the glycocalyx. The (re)synthesis of HA is dependent on the availability of its sugar substrates, thus linking glycocalyx biology directly to cellular glucose metabolism. It is therefore of particular interest to consider the consequences of dysregulated cellular glucose in diabetes for glycocalyx biology and its implications for endothelial function. This review summarizes the metabolic regulation of endothelial glycocalyx HA and its potential as a therapeutic target in diabetic vascular complications.

Closing the Mitochondrial Permeability Transition Pore in hiPSC-Derived Endothelial Cells Induces Glycocalyx Formation and Functional Maturation

Human induced pluripotent stem cells (hiPSCs) are used to study organogenesis and model disease as well as being developed for regenerative medicine. Endothelial cells are among the many cell types differentiated from hiPSCs, but their maturation and stabilization fall short of that in adult endothelium. We examined whether shear stress alone or in combination with pericyte co-culture would induce flow alignment and maturation of hiPSC-derived endothelial cells (hiPSC-ECs) but found no effects comparable with those in primary microvascular ECs. In addition, hiPSC-ECs lacked a luminal glycocalyx, critical for vasculature homeostasis, shear stress sensing, and signaling. We noted, however, that hiPSC-ECs have dysfunctional mitochondrial permeability transition pores, resulting in reduced mitochondrial function and increased reactive oxygen species. Closure of these pores by cyclosporine A improved EC mitochondrial function but also restored the glycocalyx such that alignment to flow took place. These results indicated that mitochondrial maturation is required for proper hiPSC-EC functionality.

•

hiPSC-ECs lack a functional glycocalyx and fail to align to flow

•

hiPSC-ECs have reduced mitochondrial function and increased leakage of ROS

•

Closing the mPTP with cyclosporine A induces mitochondrial maturation

•

Improved mitochondrial function restores the glycocalyx and alignment to flow

Lowering the increased intracellular pH of human-induced pluripotent stem cell-derived endothelial cells induces formation of mature Weibel-Palade bodies

Differentiation of human‐induced pluripotent stem cells (hiPSCs) into vascular endothelium is of great importance to tissue engineering, disease modeling, and use in regenerative medicine. Although differentiation of hiPSCs into endothelial‐like cells (hiPSC‐derived endothelial cells [hiPSC‐ECs]) has been demonstrated before, controversy exists as to what extent these cells faithfully reflect mature endothelium. To address this issue, we investigate hiPSC‐ECs maturation by their ability to express von Willebrand factor (VWF) and formation of Weibel‐Palade bodies (WPBs). Using multiple hiPSCs lines, hiPSC‐ECs failed to form proper VWF and WPBs, essential for angiogenesis, primary and secondary homeostasis. Lowering the increased intracellular pH (pHi) of hiPSC‐ECs with acetic acid did result in the formation of elongated WPBs. Nuclear magnetic resonance data showed that the higher pHi in hiPSC‐ECs occurred in association with decreased intracellular lactate concentrations. This was explained by decreased glycolytic flux toward pyruvate and lactate in hiPSC‐ECs. In addition, decreased expression of monocarboxylate transporter member 1, a member of the solute carrier family (SLC16A1), which regulates lactate and H+ uptake, contributed to the high pHi of hiPSC‐EC. Mechanistically, pro‐VWF dimers require the lower pH environment of the trans‐Golgi network for maturation and tubulation. These data show that while hiPSC‐ECs may share many features with mature EC, they are characterized by metabolic immaturity hampering proper EC function.

Outcomes from a mechanistic biomarker multi-arm and randomised study of liposomal MTP-PE (Mifamurtide) in metastatic and/or recurrent osteosarcoma (EuroSarc-Memos trial)

The phase III clinical study of adjuvant liposomal muramyl tripeptide (MTP-PE) in resected high-grade osteosarcoma (OS) documented positive results that have been translated into regulatory approval, supporting initial promise for innate immune therapies in OS. There remains, however, no new approved treatment such as MTP-PE for either metastatic or recurrent OS. Whilst the addition of different agents, including liposomal MTP-PE, to surgery for metastatic or recurrent high-grade osteosarcoma has tried to improve response rates, a mechanistic hiatus exists in terms of a detailed understanding the therapeutic strategies required in advanced disease. Here we report a Bayesian designed multi-arm, multi-centre, open-label phase II study with randomisation in patients with metastatic and/or recurrent OS, designed to investigate how patients with OS might respond to liposomal MTP-PE, either given alone or in combination with ifosfamide. Despite the trial closing because of poor recruitment within the allocated funding period, with no objective responses in eight patients, we report the design and feasibility outcomes for patients registered into the trial. We demonstrate the feasibility of the Bayesian design, European collaboration, tissue collection with genomic analysis and serum cytokine characterisation. Further mechanistic investigation of liposomal MTP-PE alone and in combination with other agents remains warranted in metastatic OS.

Phase 2 analysis on Covid-19-adopted etoposide (E) and cisplatin (P) regimens for patients (pts) with an advanced germ cell tumor (GCT): The CovGCT study

e17013

Background: The Covid19 pandemic has imposed risks to healthcare delivery for all cancer pts including young adults diagnosed with a GCT. Here, we examine Emergency EP (EmEP, Cohort A) and a novel 1-day Escalated-dose EP (EscEP, Cohort B) administered every 2 weeks as upfront or first-relapse therapy to minimise hospital days. Methods: Single-centre analysis in GCT pts receiving emergency and routine chemotherapy following our first National lockdown on 23rd March 2020. In Cohort A, eligible pts receive EmEP E100mg/m2, P20mg/m2 prior to EscEP within the acute setting as previously defined. In Cohort B, EscEP E500mg/m2, P60mg/m2 is compared to standard care chemotherapy BEP or POMB-ACE. Data collection includes demographics, treatment details, clinical outcome and Covid19 complications. Results: To date, we have accrued 19 pts with a median age 32 (range 18 to 65). In Cohort A, 7 pts with symptomatic high-volume disease received a median 1 cycle EmEP, 6/7 for a new GCT diagnosis and 1/7 for a first relapse, including 2 males with IGCCCG intermediate-prognosis disease, 5 females with FIGO Stage III (n = 2) and IV (n = 3) disease. One pt required higher-level support for organ dysfunction at presentation. In Cohort B, 19 pts including 7 pts from Cohort A received a median 4 cycles EscEP: 8 males (2 seminomas, 6 non-seminomas; IGCCCG good-prognosis in 4, intermediate-prognosis in 2, poor-prognosis in 2), 11 females (1 dysgerminoma, 10 non-dysgerminomas; FIGO Stage Ic in 6, III in 2, IV in 3). A majority (14/19, 74%) received EscEP for a new cancer diagnosis, 5/19 (26%) for a first relapse. Total median hospital stay: EscEP 5 days, BEP 21 days, POMB-ACE 28 days. Grade 3/4 neutropenic events: EscEP 28%, BEP 50%, POMB-ACE 43%. From April 2020, 16/16 pts were SARS-CoV-2 screened prior to each cycle: 3/19 (16%) testing positive, one prior to intubation and ventilation, 2 with asymptomatic infection. For Cohort B, at median follow-up 121 days (range 9-323 days), we have observed a complete response in 10 pts (53%), partial response in 3 pts (16%) and disease progression in 1 pt (5%). Five pts are still on treatment (26%). All pts remain alive. Conclusions: EmEP and EscEP represent safe options during the pandemic that minimise myelosuppression and total length in hospital days whilst bypassing the potential pulmonary toxicity from Bleomycin. Further follow-up will inform on long-term efficacy including a multicentre evaluation.