Methylglyoxal-Derived Nucleoside Adducts Drive Vascular Dysfunction in a RAGE-Dependent Manner

Diabetic kidney disease (DKD) is a leading cause of death in patients with diabetes. An early precursor to DKD is endothelial cell dysfunction (ECD), which often precedes and exacerbates vascular disease progression. We previously discovered that covalent adducts formed on DNA, RNA, and proteins by the reactive metabolic by-product methylglyoxal (MG) predict DKD risk in patients with type 1 diabetes up to 16 years pre-diagnosis. However, the mechanisms by which MG adducts contribute to vascular disease onset and progression remain unclear. Here, we report that the most predominant MG-induced nucleoside adducts, N2-(1-carboxyethyl)-deoxyguanosine (CEdG) and N2-(1-carboxyethyl)-guanosine (CEG), drive endothelial dysfunction. Following CEdG or CEG exposure, primary human umbilical vein endothelial cells (HUVECs) undergo endothelial dysfunction, resulting in enhanced monocyte adhesion, increased reactive oxygen species production, endothelial permeability, impaired endothelial homeostasis, and exhibit a dysfunctional transcriptomic signature. These effects were discovered to be mediated through the receptor for advanced glycation end products (RAGE), as an inhibitor for intracellular RAGE signaling diminished these dysfunctional phenotypes. Therefore, we found that not only are MG adducts biomarkers for DKD, but that they may also have a role as potential drivers of vascular disease onset and progression and a new therapeutic modality.

Mechanical stretching determines the orientation of osteoblast migration and cell division

Osteoblasts alignment and migration are involved in the directional formation of bone matrix and bone remodeling. Many studies have demonstrated that mechanical stretching controls osteoblast morphology and alignment. However, little is known about its effects on osteoblast migration. Here, we investigated changes in the morphology and migration of preosteoblastic MC3T3-E1 cells after the removal of continuous or cyclic stretching. Actin staining and time-lapse recording were performed after stretching removal. The continuous and cyclic groups showed parallel and perpendicular alignment to the stretch direction, respectively. A more elongated cell morphology was observed in the cyclic group than in the continuous group. In both stretch groups, the cells migrated in a direction roughly consistent with the cell alignment. Compared to the other groups, the cells in the cyclic group showed an increased migration velocity and were almost divided in the same direction as the alignment. To summarize, our study showed that mechanical stretching changed cell alignment and morphology in osteoblasts, which affected the direction of migration and cell division, and velocity of migration. These results suggest that mechanical stimulation may modulate the direction of bone tissue formation by inducing the directional migration and cell division of osteoblasts.

Systems Biology Analysis of Temporal Dynamics That Govern Endothelial Response to Cyclic Stretch

Endothelial cells in vivo are subjected to a wide array of mechanical stimuli, such as cyclic stretch. Notably, a 10% stretch is associated with an atheroprotective endothelial phenotype, while a 20% stretch is associated with an atheroprone endothelial phenotype. Here, a systems biology-based approach is used to present a comprehensive overview of the functional responses and molecular regulatory networks that characterize the transition from an atheroprotective to an atheroprone phenotype in response to cyclic stretch. Using primary human umbilical vein endothelial cells (HUVECs), we determined the role of the equibiaxial cyclic stretch in vitro, with changes to the radius of the magnitudes of 10% and 20%, which are representative of physiological and pathological strain, respectively. Following the transcriptome analysis of next-generation sequencing data, we identified four key endothelial responses to pathological cyclic stretch: cell cycle regulation, inflammatory response, fatty acid metabolism, and mTOR signaling, driven by a regulatory network of eight transcription factors. Our study highlights the dynamic regulation of several key stretch-sensitive endothelial functions relevant to the induction of an atheroprone versus an atheroprotective phenotype and lays the foundation for further investigation into the mechanisms governing vascular pathology. This study has significant implications for the development of treatment modalities for vascular disease.

A simple method to align cells on 3D hydrogels using 3D printed molds

Vascular smooth muscle cells align circumferentially around the vessel lumen, which allows these cells to control vascular tone by contracting and relaxing. It is essential that this circumferential alignment is recapitulated in tissue engineered blood vessels. While many methods have been reported to align cells on 2D polymeric substrates, few techniques enable cell alignment on a 3D physiologically relevant hydrogel substrate. We hypothesized that the ridges inherent to the sides of fused deposition modeling 3D printed molds could be used to topographically pattern both stiff and soft substrates and thereby align cells on flat and curved surfaces. Flat and curved molds with 150, 250, and 350 μm ridges were 3D printed and used to topographically pattern polydimethylsiloxane and gelatin-methacryloyl. The ridges transferred to both substrates with less than 10% change in ridge size. Vascular smooth muscle cells were then seeded on each substrate, and nuclear and actin alignment were quantified. Cells were highly aligned with the molded ridges to a similar extent on both the stiffer polydimethylsiloxane and the softer gelatin-methacryloyl substrates. These data confirm that fused deposition modeling 3D printed molds are a rapid, cost-effective way to topographically pattern stiff and soft substrates in varied 3D shapes. This method will enable investigators to align cells on 3D polymeric and hydrogel structures for tissue engineering and other applications.

Endothelial response to glucose: dysfunction, metabolism, and transport

The endothelial cell response to glucose plays an important role in both health and disease. Endothelial glucose-induced dysfunction was first studied in diabetic animal models and in cells cultured in hyperglycemia. Four classical dysfunction pathways were identified, which were later shown to result from the common mechanism of mitochondrial superoxide overproduction. More recently, non-coding RNA, extracellular vesicles, and sodium-glucose cotransporter-2 inhibitors were shown to affect glucose-induced endothelial dysfunction. Endothelial cells also metabolize glucose for their own energetic needs. Research over the past decade highlighted how manipulation of endothelial glycolysis can be used to control angiogenesis and microvascular permeability in diseases such as cancer. Finally, endothelial cells transport glucose to the cells of the blood vessel wall and to the parenchymal tissue. Increasing evidence from the blood-brain barrier and peripheral vasculature suggests that endothelial cells regulate glucose transport through glucose transporters that move glucose from the apical to the basolateral side of the cell. Future studies of endothelial glucose response should begin to integrate dysfunction, metabolism and transport into experimental and computational approaches that also consider endothelial heterogeneity, metabolic diversity, and parenchymal tissue interactions.

Advanced glycation end-products regulate extracellular matrix-adipocyte metabolic crosstalk in diabetes

The adipose tissue extracellular matrix (ECM) regulates adipocyte cellular metabolism and is altered in obesity and type 2 diabetes, but mechanisms underlying ECM-adipocyte metabolic crosstalk are poorly defined. Advanced glycation end-product (AGE) formation is increased in diabetes. AGE alter tissue function via direct effects on ECM and by binding scavenger receptors on multiple cell types and signaling through Rho GTPases. Our goal was to determine the role and underlying mechanisms of AGE in regulating human ECM-adipocyte metabolic crosstalk. Visceral adipocytes from diabetic and non-diabetic humans with obesity were studied in 2D and 3D-ECM culture systems. AGE is increased in adipose tissue from diabetic compared to non-diabetic subjects. Glycated collagen 1 and AGE-modified ECM regulate adipocyte glucose uptake and expression of AGE scavenger receptors and Rho signaling mediators, including the DIAPH1 gene, which encodes the human Diaphanous 1 protein (hDia1). Notably, inhibition of hDia1, but not scavenger receptors RAGE or CD36, attenuated AGE-ECM inhibition of adipocyte glucose uptake. These data demonstrate that AGE-modification of ECM contributes to adipocyte insulin resistance in human diabetes, and implicate hDia1 as a potential mediator of AGE-ECM-adipocyte metabolic crosstalk.

Biofabrication strategies for creating microvascular complexity

Design and fabrication of effective biomimetic vasculatures constitutes a relevant and yet unsolved challenge, lying at the heart of tissue repair and regeneration strategies. Even if cell growth is achieved in 3D tissue scaffolds or advanced implants, tissue viability inevitably requires vascularization, as diffusion can only transport nutrients and eliminate debris within a few hundred microns. This engineered vasculature may need to mimic the intricate branching geometry of native microvasculature, referred to herein as vascular complexity, to efficiently deliver blood and recreate critical interactions between the vascular and perivascular cells as well as parenchymal tissues. This review first describes the importance of vascular complexity in labs- and organs-on-chips, the biomechanical and biochemical signals needed to create and maintain a complex vasculature, and the limitations of current 2D, 2.5D, and 3D culture systems in recreating vascular complexity. We then critically review available strategies for design and biofabrication of complex vasculatures in cell culture platforms, labs- and organs-on-chips, and tissue engineering scaffolds, highlighting their advantages and disadvantages. Finally, challenges and future directions are outlined with the hope of inspiring researchers to create the reliable, efficient and sustainable tools needed for design and biofabrication of complex vasculatures.

Quantitative Studies of Endothelial Cell Fibronectin and Filamentous Actin (F-Actin) Coalignment in Response to Shear Stress

Both fibronectin (FN) and filamentous actin (F-actin) fibers play a critical role for endothelial cells (ECs) in responding to shear stress and modulating cell alignment and functions. FN is dynamically coupled to the F-actin cytoskeleton via focal adhesions. However, it is unclear how ECs cooperatively remodel their subcellular FN matrix and intracellular F-actin cytoskeleton in response to shear stress. Current studies are hampered by the lack of a reliable and sensitive quantification method of FN orientation. In this study, we developed a MATLAB-based feature enhancement method to quantify FN and F-actin orientation. The role of F-actin in FN remodeling was also studied by treating ECs with cytochalasin D. We have demonstrated that FN and F-actin codistributed and coaligned parallel to the flow direction, and that F-actin alignment played an essential role in regulating FN alignment in response to shear stress. Our findings offer insight into how ECs cooperatively remodel their subcellular ECM and intracellular F-actin cytoskeleton in response to mechanical stimuli, and are valuable for vascular tissue engineering.

Hyperglycemia, tumorigenesis, and chronic inflammation

Hyperglycemia is the most prominent sign that characterizes diabetes. Hyperglycemia favors malignant cell growth by providing energy to cancer cells. Clinical studies also showed an increased risk of diabetes being associated with different types of cancers. In addition, poorly regulated glucose metabolism in diabetic patients is often found with increased levels of chronic inflammatory markers, e.g., interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α, and emerging evidence has highlighted activation of the immune response in the progression and development of cancer cells. Therefore, uncontrolled proinflammatory responses could conceivably create a chronic inflammatory state, promoting a tumor-favorable microenvironment and potentially triggering immune overactivation and cancer growth. To further understand how hyperglycemia contributes to immune overactivation, the tumor microenvironment and the development of chronic inflammation-associated tumors may provide insights into tumor biology and immunology. This paper provides a brief introduction to hyperglycemia-associated diseases, followed by a comprehensive overview of the current findings of regulatory molecular mechanisms of glycosylation on proteoglycans in the extracellular matrix under hyperglycemic conditions. Then, the authors discuss the role of hyperglycemia in tumorigenesis (particularly in prostate, liver, colorectal, and pancreatic cancers), as well as the contribution of hyperglycemia to chronic inflammation. The authors end with a brief discussion on the future perspectives of hyperglycemia/tumorigenesis and potential applications of alternative/effective therapeutic strategies for hyperglycemia-associated cancers.

Problem-Based Learning in Biomechanics: Advantages, Challenges, and Implementation Strategies

Problem-based learning (PBL) has been shown to be effective in biomedical engineering education, particularly in motivating student learning, increasing knowledge retention, and developing problem solving, communication, and teamwork skills. However, PBL adoption remains limited by real challenges in effective implementation. In this paper, we review the literature on advantages and challenges of PBL and present our own experiences. We also provide practical guidelines for implementing PBL, including two examples of PBL modules from biomechanics courses at two different institutions. Overall, we conclude that the benefits for both professors and students support the use of PBL in biomedical engineering education.

Mechanical Injury Induces Brain Endothelial-Derived Microvesicle Release: Implications for Cerebral Vascular Injury during Traumatic Brain Injury

It is well established that the endothelium responds to mechanical forces induced by changes in shear stress and strain. However, our understanding of vascular remodeling following traumatic brain injury (TBI) remains incomplete. Recently published studies have revealed that lung and umbilical endothelial cells produce extracellular microvesicles (eMVs), such as microparticles, in response to changes in mechanical forces (blood flow and mechanical injury). Yet, to date, no studies have shown whether brain endothelial cells produce eMVs following TBI. The brain endothelium is highly specialized and forms the blood-brain barrier (BBB), which regulates diffusion and transport of solutes into the brain. This specialization is largely due to the presence of tight junction proteins (TJPs) between neighboring endothelial cells. Following TBI, a breakdown in tight junction complexes at the BBB leads to increased permeability, which greatly contributes to the secondary phase of injury. We have therefore tested the hypothesis that brain endothelium responds to mechanical injury, by producing eMVs that contain brain endothelial proteins, specifically TJPs. In our study, primary human adult brain microvascular endothelial cells (BMVEC) were subjected to rapid mechanical injury to simulate the abrupt endothelial disruption that can occur in the primary injury phase of TBI. eMVs were isolated from the media following injury at 2, 6, 24, and 48 h. Western blot analysis of eMVs demonstrated a time-dependent increase in TJP occludin, PECAM-1 and ICAM-1 following mechanical injury. In addition, activation of ARF6, a small GTPase linked to extracellular vesicle production, was increased after injury. To confirm these results in vivo, mice were subjected to sham surgery or TBI and blood plasma was collected 24 h post-injury. Isolation and analysis of eMVs from blood plasma using cryo-EM and flow cytometry revealed elevated levels of vesicles containing occludin following brain trauma. These results indicate that following TBI, the cerebral endothelium undergoes vascular remodeling through shedding of eMVs containing TJPs and endothelial markers. The detection of this shedding potentially allows for a novel methodology for real-time monitoring of cerebral vascular health (remodeling), BBB status and neuroinflammation following a TBI event.

High-density lipoprotein of patients with breast cancer complicated with type 2 diabetes mellitus promotes cancer cells adhesion to vascular endothelium via ICAM-1 and VCAM-1 upregulation

Adhesion of disseminating tumor cells to vascular endothelium is a pivotal starting point in the metastasis cascade. We have shown previously that diabetic high-density lipoprotein (HDL) has the capability of promoting breast cancer metastasis, and this report summarizes our more recent work studying the role of abnormal HDL in facilitating the adhesion of the circulating tumor cells to the endothelium. This is an initiating step in breast cancer metastasis, and this work assesses the role of ICAM-1 and VCAM-1 in this process. MDA-MB-231, MCF 7, and human umbilical vein endothelial cells (HUVECs) were treated with normal HDL from healthy controls (N-HDL), HDL from breast cancer patients (B-HDL), or HDL from breast cancer patients complicated with type 2 diabetes mellitus (BD-HDL), and the cell adhesion abilities were determined. ICAM-1 and VCAM-1 expression as well as the protein kinase C (PKC) activity were evaluated. The effect of PKC inhibitor and PKC siRNA on adhesion was also studied. The immunohistochemical staining of ICAM-1, VCAM-1, and E-selectin from breast cancer patients and breast cancer patients complicated with type 2 diabetes mellitus (T2DM) were examined. Our results indicate that BD-HDL promoted an increase in breast cancer cell adhesion to HUVECs and stimulated higher ICAM-1 and VCAM-1 expression on the cells surface of both breast cancer and HUVEC cells, along with the activation of PKC. Increased tumor cell (TC)-HUVEC adhesion, as well as ICAM-1 and VCAM-1 expression induced by BD-HDL, could be inhibited by staurosporine and PKC siRNA. In addition, a Db/db type 2 diabetes mouse model has more TC-Vascular Endothelium adhesion compared to a normal model. However, BD patients have a lower expression of ICAM-1, VCAM-1, and E-selectin in their tumor tissues. BD-HDL facilitates the adhesion of tumor cells to vascular endothelium by upregulating the expression of ICAM-1 and VCAM-1, thereby promoting the initial progression of breast cancer metastasis. This work indicates a prospective utilization of HDL-based strategies in the treatment of breast cancer patients with type 2 diabetes.