Blood Vessel Basement Membrane Alterations in Human Retinal Microaneurysms During Aging

Pericyte in retinal vascular diseases: A multifunctional regulator and potential therapeutic target

Retinal vascular diseases (RVDs), in particular diabetic retinopathy, retinal vein occlusion, and retinopathy of prematurity, are leading contributors to blindness. The pathogenesis of RVD involves vessel dilatation, leakage, and occlusion; however, the specific underlying mechanisms remain unclear. Recent findings have indicated that pericytes (PCs), as critical members of the vascular mural cells, significantly contribute to the progression of RVDs, including detachment from microvessels, alteration of contractile and secretory properties, and excessive production of the extracellular matrix. Moreover, PCs are believed to have mesenchymal stem properties and, therefore, might contribute to regenerative therapy. Here, we review novel ideas concerning PC characteristics and functions in RVDs and discuss potential therapeutic strategies based on PCs, including the targeting of pathological signals and cell-based regenerative treatments.

Extracellular vesicles from senescent mesenchymal stromal cells are defective and cannot prevent osteoarthritis

Age is the most important risk factor in degenerative diseases such as osteoarthritis (OA), which is associated with the accumulation of senescent cells in the joints. Here, we aimed to assess the impact of senescence on the therapeutic properties of extracellular vesicles (EVs) from human fat mesenchymal stromal cells (ASCs) in OA. We generated a model of DNA damage-induced senescence in ASCs using etoposide and characterized EVs isolated from their conditioned medium (CM). Senescent ASCs (S-ASCs) produced 3-fold more EVs (S-EVs) with a slightly bigger size and that contain 2-fold less total RNA. Coculture experiments showed that S-ASCs were as efficient as healthy ASCs (H-ASCs) in improving the phenotype of OA chondrocytes cultured in resting conditions but were defective when chondrocytes were proliferating. S-EVs were also impaired in their capacity to polarize synovial macrophages towards an anti-inflammatory phenotype. A differential protein cargo mainly related to inflammation and senescence was detected in S-EVs and H-EVs. Using the collagenase-induced OA model, we found that contrary to H-EVs, S-EVs could not protect mice from cartilage damage and joint calcifications, and were less efficient in protecting subchondral bone degradation. In addition, S-EVs induced a pro-catabolic and pro-inflammatory gene signature in the joints of mice shortly after injection, while H-EVs decreased hypertrophic, catabolic and inflammatory pathways. In conclusion, S-EVs are functionally impaired and cannot protect mice from developing OA.

Multilamellated Basement Membranes in the Capillary Network of Alveolar Capillary Dysplasia

A minimal diffusion barrier is key to the pulmonary gas exchange. In alveolar capillary dysplasia (ACD), a rare genetically driven disease of early infancy, this crucial fibrovascular interface is compromised while the underlying pathophysiology is insufficiently understood. Recent in-depth analyses of vascular alterations in adult lung disease encouraged researchers to extend these studies to ACD and compare the changes of the microvasculature. Lung tissue samples of children with ACD (n = 12), adults with non-specific interstitial pneumonia (n = 12), and controls (n = 20) were studied using transmission electron microscopy, single-gene sequencing, immunostaining, exome sequencing, and broad transcriptome profiling. In ACD, pulmonary capillary basement membranes were hypertrophied, thickened, and multilamellated. Transcriptome profiling revealed increased CDH5, COL4A1, COL15A1, PTK2B, and FN1 and decreased VIT expression, confirmed by immunohistochemistry. In contrast, non-specific interstitial pneumonia samples showed a regular basement membrane architecture with preserved VIT expression but also increased COL15A1+ vessels. This study provides insight into the ultrastructure and pathophysiology of ACD. The lack of normally developed lung capillaries appeared to cause a replacement by COL15A1+ vessels, a mechanism recently described in interstitial lung disease. The VIT loss and FN1 overexpression might contribute to the unique appearance of basement membranes in ACD. Future studies are needed to explore the therapeutic potential of down-regulating the expression of FN1 and balancing VIT deficiency.

Intraretinal Macroaneurysms and Multimodal Imaging: A Retrospective Analysis

Purpose

To analyze the multimodal imaging characteristics of intraretinal macroaneurysms.

Patients and Methods

Intraretinal aneurysms larger than 150 μm in diameter on fluorescein angiography were termed as intraretinal macroaneurysm and grouped as primary and secondary according to the absence or presence of any coexisting posterior segment diseases.

Results

A total of 20 intraretinal macroaneurysms were observed in 18 eyes of 18 patients. Mean age of the cohort was 65.44 ± 9.14 years (Range; 49-82 years). Mean diameters of intraretinal macroaneurysms were 238.20 ± 61.12 μm (Range; 163.00-292.50 μm) and 242.72 ± 49.58 μm (Range; 168.00-328.00 μm) on fluorescein angiography and optical coherence tomography, respectively. Primary group had 10 eyes with 11 intraretinal macroaneurysms, whereas eight eyes had nine intraretinal macroaneurysms in the secondary group. Three of the eight eyes (37.5%) had diabetic retinopathy, four (50%), retinal vein occlusion, and one (12.5%), posterior uveitis in the secondary group. No statistically significant differences were found between the two groups in terms of age, sex, presence of intraretinal or subretinal fluid, the mean age, the mean central macular thickness, the mean distance of intraretinal macroaneurysms from the fovea, the mean diameter of intraretinal macroaneurysms measured on fluorescein angiography, and the mean diameter of intraretinal macroaneurysms measured on optical coherence tomography. Presence of intraretinal fluid was significantly more frequent than the presence of subretinal fluid in all eyes (p = 0.004).

Conclusion

Intraretinal macroaneurysms are diagnosed more and more with the utilization of multimodal imaging techniques. We propose a simple classification system in order to help achieving a standardized terminology and ensure consistent understanding. The classification can be simplified as primary or secondary intraretinal macroaneurysm according to the absence or presence of the associated posterior segment disorders.

Pericyte heterogeneity identified by 3D ultrastructural analysis of the microvessel wall

Confident identification of pericytes (PCs) remains an obstacle in the field, as a single molecular marker for these unique perivascular cells remains elusive. Adding to this challenge is the recent appreciation that PC populations may be heterogeneous, displaying a range of morphologies within capillary networks. We found additional support on the ultrastructural level for the classification of these PC subtypes-"thin-strand" (TSP), mesh (MP), and ensheathing (EP)-based on distinct morphological characteristics. Interestingly, we also found several examples of another cell type, likely a vascular smooth muscle cell, in a medial layer between endothelial cells (ECs) and pericytes (PCs) harboring characteristics of the ensheathing type. A conserved feature across the different PC subtypes was the presence of extracellular matrix (ECM) surrounding the vascular unit and distributed in between neighboring cells. The thickness of this vascular basement membrane was remarkably consistent depending on its location, but never strayed beyond a range of 150-300 nm unless thinned to facilitate closer proximity of neighboring cells (suggesting direct contact). The density of PC-EC contact points ("peg-and-socket" structures) was another distinguishing feature across the different PC subtypes, as were the apparent contact locations between vascular cells and brain parenchymal cells. In addition to this thinning, the extracellular matrix (ECM) surrounding EPs displayed another unique configuration in the form of extensions that emitted out radially into the surrounding parenchyma. Knowledge of the origin and function of these structures is still emerging, but their appearance suggests the potential for being mechanical elements and/or perhaps signaling nodes via embedded molecular cues. Overall, this unique ultrastructural perspective provides new insights into PC heterogeneity and the presence of medial cells within the microvessel wall, the consideration of extracellular matrix (ECM) coverage as another PC identification criteria, and unique extracellular matrix (ECM) configurations (i.e., radial extensions) that may reveal additional aspects of PC heterogeneity.

Mitochondrial dysfunction induces ALK5-SMAD2-mediated hypovascularization and arteriovenous malformations in mouse retinas

Although mitochondrial activity is critical for angiogenesis, its mechanism is not entirely clear. Here we show that mice with endothelial deficiency of any one of the three nuclear genes encoding for mitochondrial proteins, transcriptional factor (TFAM), respiratory complex IV component (COX10), or redox protein thioredoxin 2 (TRX2), exhibit retarded retinal vessel growth and arteriovenous malformations (AVM). Single-cell RNA-seq analyses indicate that retinal ECs from the three mutant mice have increased TGFβ signaling and altered gene expressions associated with vascular maturation and extracellular matrix, correlating with vascular malformation and increased basement membrane thickening in microvesels of mutant retinas. Mechanistic studies suggest that mitochondrial dysfunction from Tfam, Cox10, or Trx2 depletion induces a mitochondrial localization and MAPKs-mediated phosphorylation of SMAD2, leading to enhanced ALK5-SMAD2 signaling. Importantly, pharmacological blockade of ALK5 signaling or genetic deficiency of SMAD2 prevented retinal vessel growth retardation and AVM in all three mutant mice. Our studies uncover a novel mechanism whereby mitochondrial dysfunction via the ALK5-SMAD2 signaling induces retinal vascular malformations, and have therapeutic values for the alleviation of angiogenesis-associated human retinal diseases.

Retinal organoids and microfluidic chip-based approaches to explore the retinitis pigmentosa with USH2A mutations

Retinitis pigmentosa (RP) is a leading cause of vision impairment and blindness worldwide, with limited medical treatment options. USH2A mutations are one of the most common causes of non-syndromic RP. In this study, we developed retinal organoids (ROs) and retinal pigment epithelium (RPE) cells from induced pluripotent stem cells (iPSCs) of RP patient to establish a sustainable in vitro RP disease model. RT-qPCR, western blot, and immunofluorescent staining assessments showed that USH2A mutations induced apoptosis of iPSCs and ROs, and deficiency of the extracellular matrix (ECM) components. Transcriptomics and proteomics findings suggested that abnormal ECM-receptor interactions could result in apoptosis of ROs with USH2A mutations via the PI3K-Akt pathway. To optimize the culture conditions of ROs, we fabricated a microfluidic chip to co-culture the ROs with RPE cells. Our results showed that this perfusion system could efficiently improve the survival rate of ROs. Further, ECM components such as laminin and collagen IV of ROs in the RP group were upregulated compared with those maintained in static culture. These findings illustrate the potential of microfluidic chip combined with ROs technology in disease modelling for RP.

Fluorescein Leakage and Optical Coherence Tomography Angiography Features of Microaneurysms in Diabetic Retinopathy

RESULTS

Thirty-six, fifty-two, and seventy-nine MAs showed no, mild, and severe leakage on FA, respectively. Most MAs (61.7%) were centered in the inner nuclear layer. Cystoid spaces were observed adjacent to 60 (35.9%) MAs. MAs with severe leakage had a statistically higher flow proportion compared to MAs with no or mild leakage (both P < 0.001). Only 112 MAs (67.1%) were visualized in the OCTA en face images, while 165 MAs (98.8%) could be visualized in the OCT en face images. The location of MAs did not associate significantly with FA leakage status. The presence of nearby cystoid spaces and higher flow proportion by OCT B-scan with flow overlay correlated significantly with FA leakage status.

CONCLUSION

The flow proportion of MAs observed on OCT B-scans with flow overlay might be a potential biomarker to identify leaking MAs. A combination of OCT B-scan, OCT en face, and OCTA en face images increased the detection rate of diabetic MAs in a noninvasive way.

Angiotensin II is a crucial factor in retinal aneurysm formation

Retinal arterial macroaneurysms are characterized by the acquired fusiform or saccular dilatations of the retinal artery. Angiotensin II (Ang II) is a major signal molecule of the renin-angiotensin system, which exerts a range of pathogenic actions that are relevant to retinal vascular abnormalities. We aimed to study the effect of Ang II on retinal vessels and explore its relationship with retinal aneurysmal disease. C57BL/6J male mice were administered Ang II at 1000 ng/kg/min for 28 days, and the mice given saline served as controls. The mice in the treatment group were treated once daily by gastric gavage of candesartan cilexetil (an antagonist of Ang II type 1 (AT1) receptor) at 100 mg/kg/day. The in vivo imaging of murine retinas was performed using fundus photography, optical coherence tomography, fluorescein angiography, and indocyanine green angiography at 7th, 14th, and 28th days of infusion. At the end of the infusion and treatment, the morphological changes were evaluated by histopathological examination and electron microscopy; the levels of related proteins in murine retinas were examined by antibody array and Western blot analyses. We found that Ang II infusion induced aneurysm formation in mice retina, which presented as either solitary aneurysms or retinal arterial beading. The aneurysm formation was often accompanied with vessel leakage. Moreover, Ang II infusion itself may result in increased vascular permeability and ganglion cell and inner plexiform layer thickening. The blockade of AT1 receptors by systemic administration of candesartan cilexetil alleviated the Ang II-induced retinal vasculopathy. The protein level analysis further showed that Ang II upregulated IL-1β, PDGFR-β, and MMP-9 expression, and the expression of IL-1β could be inhibited by AT1 receptor antagonist. Our study provides evidence that Ang II is a crucial factor in retinal aneurysm formation and vessel leakage. It is probably the combined effect of Ang II on vessel inflammatory response, pericyte function, and extracellular matrix remodeling that predisposes the retinal arterial wall to aneurysm formation and blood-retinal barrier breakdown.

Cell-derived extracellular matrix materials for tissue engineering

The involvement of cell-derived extracellular matrix (CDM) in assembling tissue engineering scaffolds has yielded significant results. CDM possesses excellent characteristics, such as ideal cellular microenvironment mimicry and good biocompatibility, which make it a popular research direction in the field of bionanomaterials. CDM has significant advantages as an expansion culture substrate for stem cells, including stabilization of phenotype, reversal of senescence, and guidance of specific differentiation. In addition, the applications of CDM-assembled tissue engineering scaffolds for disease simulation and tissue organ repair are comprehensively summarized; the focus is mainly on bone and cartilage repair, skin defect or wound healing, engineered blood vessels, peripheral nerves, and periodontal tissue repair. We consider CDM a highly promising bionic biomaterial for tissue engineering applications and propose a vision for its comprehensive development.

Selective Photocoagulation of Capillary Macroaneurysms by Navigated Focal Laser

BACKGROUND AND OBJECTIVE

To evaluate the anatomical and functional outcome of selective photocoagulation of capillary macroaneurysms (CMAs) by navigated focal laser.

PATIENTS AND METHODS

Consecutive patients with solitary or secondary CMAs greater than 150 mm in diameter were included in this analysis. All patients were treated with navigated focal laser and received multimodal imaging.

RESULTS

Seventeen eyes of 17 patients were retrospectively analyzed. Navigated laser photocoagulation of the CMAs successfully occluded 100% of the CMAs, inducing significative improvement in best-corrected visual acuity at 3 (P = .002) and 6 months (P = .001) and a decrease in central macular thickness (CMT) at 3 (P = .0004) and 6 months (P = .0004).

CONCLUSIONS

Solitary or secondary CMAs arising from retinal capillaries are candidates for navigated laser treatment. Navigated focal treatment was able to close all CMAs in this series with an improvement in vision and CMT. [Ophthalmic Surg Lasers Imaging Retina. 2021;52:366-373.].

Subretinal leakage of a retinal capillary macroaneurysm - a case report

BACKGROUND

Report a rare case of retinal capillary macroaneurysm with associated subretinal fluid.

CASE PRESENTATION

A 71-year-old male underwent full ophthalmic examination including Optical Coherence Tomography (OCT), Fluorescein Angiography (FA). Fundus examination showed moderate non-proliferative diabetic retinopathy of both eyes with scattered microaneurysms. On initial visit, FA displayed a hyperfluorescent lesion with leakage on late frames in the left eye. OCT revealed the lesion to be spheroid with a hyperreflective wall and hyporeflective lumen in the inner retina, corresponding to a capillary macroaneurysm. Intraretinal cystic fluid surrounded the lesion. On subsequent visit 7 months later, subretinal fluid in the location of the capillary macroaneurysm was noted on OCT. Vision was maintained at 20/30-2 OD, 20/40 OS throughout. No treatment was necessary.

CONCLUSION

Subretinal fluid from the capillary macroaneurysm likely developed from its juxtafoveal location and discontinuity of the external limiting membrane (ELM); a barrier preventing flow of intraretinal fluid to the outer retina.

Neurovascular unit in diabetic retinopathy: pathophysiological roles and potential therapeutical targets

Diabetic retinopathy (DR), one of the common complications of diabetes, is the leading cause of visual loss in working-age individuals in many industrialized countries. It has been traditionally regarded as a purely microvascular disease in the retina. However, an increasing number of studies have shown that DR is a complex neurovascular disorder that affects not only vascular structure but also neural tissue of the retina. Deterioration of neural retina could precede microvascular abnormalities in the DR, leading to microvascular changes. Furthermore, disruption of interactions among neurons, vascular cells, glia and local immune cells, which collectively form the neurovascular unit, is considered to be associated with the progression of DR early on in the disease. Therefore, it makes sense to develop new therapeutic strategies to prevent or reverse retinal neurodegeneration, neuroinflammation and impaired cell-cell interactions of the neurovascular unit in early stage DR. Here, we present current perspectives on the pathophysiology of DR as a neurovascular disease, especially at the early stage. Potential novel treatments for preventing or reversing neurovascular injuries in DR are discussed as well.

Microvascular cells: A special focus on heterogeneity of pericytes in diabetes associated complications

Pericytes (PC) are microvascular mural cells that make specific cell-to-cell contacts with the endothelial cells (EC). These cells are obligatory constituents of the microvessels including the retinal vasculature and they serve as regulators of vascular development, stabilization, maturation and remodeling. During early stages of diabetic retinopathy (DR), apoptotic loss of PC surrounding the retinal vasculature occurs. This may lead to reduced vessel stability, the onset of EC apoptosis, and subsequent retinal ischemia leading to angiogenesis and eventually, severe vision loss due to late proliferative diabetic retinopathy (PDR). Similarly, diabetic nephropathy (DN) is a chronic kidney disease due to hyperglycemia that particularly affects renal PC. Chronic high blood glucose level causes migration of peritubular PC away from the capillary into the interstitial space, which destabilizes the micro vessels, resulting in microvascular rarefaction. In both diabetes associated complications, the identification of specific biomarkers is necessary to stabilize the PC at an early stage. This review largely covers the importance of PC towards the pathogenesis of diabetes associated complications, and their heterogeneity in healthy and angiogenic vasculature.

RETINAL CAPILLARY MACROANEURYSMS

PURPOSE

To investigate eyes with solitary large aneurysms arising from retinal capillaries.

METHODS

Consecutive patients with aneurysms greater than 200 µm in diameter were evaluated with a comprehensive ophthalmologic examination including optical coherence tomography, optical coherence tomography angiography, and fluorescein angiography. The aneurysms were solitary in the sense, and there was only one aneurysm larger than the threshold diameter and a few or no other aneurysms.

RESULTS

There were 5 patients, 3 male patients, who had aneurysms that reached a maximal mean size of 273.4 µm. One patient had stable diabetic retinopathy and had a documented growth of a capillary aneurysm to 331 µm over an 8-year 7-month period until the aneurysm was associated with widespread edema. The remaining 4 patients did not have diabetes or any discernable retinal vascular disease. Anti-vascular endothelial growth factor treatment was associated with a partial response in one patient and no apparent response in the others. Laser photocoagulation of the aneurysms resulted in resolution of the edema and involution of the lesions.

CONCLUSION

Large aneurysms arising from retinal capillaries occur and have a candidate name of retinal capillary macroaneurysms. Histologic evaluation of retinal capillary aneurysms shows the presence of matrix metalloproteinase-9, which may function to decrease the wall strength in the face of increasing wall tension from aneurysmal expansion, as predicted by LaPlace's law. Thus, retinal capillary macroaneurysms may have multiple forces driving their formation.

Retinopathy secondary to multiple myeloma treated with bevacizumab

The case is presented on an 80-year-old woman with IgA multiple myeloma (MM), who developed retinal changes similar to mild non-proliferative diabetic retinopathy, with micro-aneurysms and intraretinal fluid. The patient was treated with systemic chemotherapy for MM, and with bevacizumab intravitreal injections, with control of her ocular disorder for 22 months. Anti-angiogenic therapy can be useful in the control of retinopathy secondary to MM, as long as the systemic disease has been controlled.

Laminin α4 overexpression in the anterior lens capsule may contribute to the senescence of human lens epithelial cells in age-related cataract

Senescence is a leading cause of age-related cataract (ARC). The current study indicated that the senescence-associated protein, p53, total laminin (LM), LMα4, and transforming growth factor-beta1 (TGF-β1) in the cataractous anterior lens capsules (ALCs) increase with the grades of ARC. In cataractous ALCs, patient age, total LM, LMα4, TGF-β1, were all positively correlated with p53. In lens epithelial cell (HLE B-3) senescence models, matrix metalloproteinase-9 (MMP-9) alleviated senescence by decreasing the expression of total LM and LMα4; TGF-β1 induced senescence by increasing the expression of total LM and LMα4. Furthermore, MMP-9 silencing increased p-p38 and LMα4 expression; anti-LMα4 globular domain antibody alleviated senescence by decreasing the expression of p-p38 and LMα4; pharmacological inhibition of p38 MAPK signaling alleviated senescence by decreasing the expression of LMα4. Finally, in cataractous ALCs, positive correlations were found between LMα4 and total LM, as well as between LMα4 and TGF-β1. Taken together, our results implied that the elevated LMα4, which was possibly caused by the decreased MMP-9, increased TGF-β1 and activated p38 MAPK signaling during senescence, leading to the development of ARC. LMα4 and its regulatory factors show potential as targets for drug development for prevention and treatment of ARC.

The pericyte microenvironment during vascular development

Vascular pericytes provide critical contributions to the formation and integrity of the blood vessel wall within the microcirculation. Pericytes maintain vascular stability and homeostasis by promoting endothelial cell junctions and depositing extracellular matrix (ECM) components within the vascular basement membrane, among other vital functions. As their importance in sustaining microvessel health within various tissues and organs continues to emerge, so does their role in a number of pathological conditions including cancer, diabetic retinopathy, and neurological disorders. Here, we review vascular pericyte contributions to the development and remodeling of the microcirculation, with a focus on the local microenvironment during these processes. We discuss observations of their earliest involvement in vascular development and essential cues for their recruitment to the remodeling endothelium. Pericyte involvement in the angiogenic sprouting context is also considered with specific attention to crosstalk with endothelial cells such as through signaling regulation and ECM deposition. We also address specific aspects of the collective cell migration and dynamic interactions between pericytes and endothelial cells during angiogenic sprouting. Lastly, we discuss pericyte contributions to mechanisms underlying the transition from active vessel remodeling to the maturation and quiescence phase of vascular development.

Extracellular matrix scaffolding in angiogenesis and capillary homeostasis

The extracellular matrix (ECM) of blood vessels, which is composed of both the vascular basement membrane (BM) and the interstitial ECM is identified as a crucial component of the vasculature. We here focus on the unique molecular composition and scaffolding of the capillary ECM, which provides structural support to blood vessels and regulates properties of endothelial cells and pericytes. The major components of the BM are collagen IV, laminins, heparan sulfate proteoglycans and nidogen and also associated proteins such as collagen XVIII and fibronectin. Their organization and scaffolding in the BM is required for proper capillary morphogenesis and maintenance of vascular homeostasis. The BM also regulates vascular mechanosensing. A better understanding of the mechanical and structural properties of the vascular BM and interstitial ECM therefore opens new perspectives to control physiological and pathological angiogenesis and vascular homeostasis. The overall aim of this review is to explain how ECM scaffolding influences angiogenesis and capillary integrity.

The role of the cell-matrix interface in aging and its interaction with the renin-angiotensin system in the aged vasculature

The extracellular matrix (ECM) is an intricate network that provides structural and anchoring support to cells in order to stabilize cell morphology and tissue architecture. The ECM also controls many aspects of the cell's dynamic behavior and fate through its ongoing, bidirectional interaction with cells. These interactions between the cell and components of the surrounding ECM are implicated in several biological processes, including development and adult tissue repair in response to injury, throughout the lifespan of multiple species. The present review gives an overview of the growing evidence that cell-matrix interactions play a pivotal role in the aging process. The focus of the first part of the article is on recent studies using cell-derived decellularized ECM, which strongly suggest that age-related changes in the ECM induce cellular senescence, a well-recognized hallmark of aging. This is followed by a review of findings from genetic studies indicating that changes in genes involved in cell-ECM adhesion and matrix-mediated intracellular signaling cascades affect longevity. Finally, mention is made of novel data proposing an intricate interplay between cell-matrix interactions and the renin-angiotensin system that may have a significant impact on mammalian arterial stiffness with age.

Basement Membranes in Development and Disease

The basement membrane is a thin but dense, sheet-like specialized type of extracellular matrix that has remarkably diverse functions tailored to individual tissues and organs. Tightly controlled spatial and temporal changes in its composition and structure contribute to the diversity of basement membrane functions. These different basement membranes undergo dynamic transformations throughout animal life, most notably during development. Numerous developmental mechanisms are regulated or mediated by basement membranes, often by a combination of molecular and mechanical processes. A particularly important process involves cell transmigration through a basement membrane because of its link to cell invasion in disease. While developmental and disease processes share some similarities, what clearly distinguishes the two is dysregulation of cells and extracellular matrices in disease. With its relevance to many developmental and disease processes, the basement membrane is a vitally important area of research that may provide novel insights into biological mechanisms and development of innovative therapeutic approaches. Here we present a review of developmental and disease dynamics of basement membranes in Caenorhabditis elegans, Drosophila, and vertebrates.

Diabetes-related changes in the protein composition and the biomechanical properties of human retinal vascular basement membranes

Basement membranes (BMs) are specialized sheets of extracellular matrix that outline epithelial cell layers, muscle fibers, blood vessels, and peripheral nerves. A well-documented histological hallmark of progressing diabetes is a major increase in vascular BM thickness. In order to investigate whether this structural change is accompanied by a change in the protein composition, we compared the proteomes of retinal vascular BMs from diabetic and non-diabetic donors by using LC-MS/MS. Data analysis showed that seventeen extracellular matrix (ECM)-associated proteins were more abundant in diabetic than non-diabetic vascular BMs. Four ECM proteins were more abundant in non-diabetic than in diabetic BMs. Most of the over-expressed proteins implicate a complement-mediated chronic inflammatory process in the diabetic retinal vasculature. We also found an up-regulation of norrin, a protein that is known to promote vascular proliferation, possibly contributing to the vascular remodeling during diabetes. Many of the over-expressed proteins were localized to microvascular aneurisms. Further, the overall stoichiometry of proteins was changed, such that the relative abundance of collagens in BMs from diabetic patients was higher than normal. Biomechanical measurements of vascular BM flat mounts using AFM showed that their outer surface was softer than normal.