The anterior chamber of the eye is a transplantation site that supports and enables visualisation of beta cell development in mice

The anterior chamber of the eye technology and its anatomical, optical, and immunological bases

The anterior chamber of the eye (ACE) is distinct in its anatomy, optics, and immunology. This guarantees that the eye perceives visual information in the context of physiology even when encountering adverse incidents like inflammation. In addition, this endows the ACE with the special nursery bed iris enriched in vasculatures and nerves. The ACE constitutes a confined space enclosing an oxygen/nutrient-rich, immune-privileged, and less stressful milieu as well as an optically transparent medium. Therefore, aside from visual perception, the ACE unexpectedly serves as an excellent transplantation site for different body parts and a unique platform for noninvasive, longitudinal, and intravital microimaging of different grafts. On the basis of these merits, the ACE technology has evolved from the prototypical through the conventional to the advanced version. Studies using this technology as a versatile biomedical research platform have led to a diverse range of basic knowledge and in-depth understanding of a variety of cells, tissues, and organs as well as artificial biomaterials, pharmaceuticals, and abiotic substances. Remarkably, the technology turns in vivo dynamic imaging of the morphological characteristics, organotypic features, developmental fates, and specific functions of intracameral grafts into reality under physiological and pathological conditions. Here we review the anatomical, optical, and immunological bases as well as technical details of the ACE technology. Moreover, we discuss major achievements obtained and potential prospective avenues for this technology.

Challenges in stem cell-derived islet replacement therapy can be overcome

In this Commentary, we echo the conclusions of a recent review titled “The promise of stem cell-derived islet replacement therapy,” which highlighted recent advances in producing glucose responsive “islets” from stem cells and the benefits of their use in islet transplant therapy in type 1 diabetes (T1D). The review also outlined the status of clinical islet transplantation and the challenges that have prevented it from reaching its full therapeutic promise. We agree with the conclusions of the review and suggest that the identified challenges may be overcome by using the eye anterior chamber as an islet transplant site. We anticipate that the combination of stem cell-derived islets and intraocular transplant could help this promising T1D therapy reach full fruition.

Long Term Rescue of the TSH Receptor Knock-Out Mouse - Thyroid Stem Cell Transplantation Restores Thyroid Function

The synergistic activation of transcription factors can lead to thyroid progenitor cell speciation. We have previously shown in vitro that mouse or human stem cells, expressing the transcription factors NKx2-1 and Pax8, can differentiate into thyroid neo-follicular structures (TFS). We now show that syngeneic mouse TFS when implanted into hypothyroid TSH receptor knockout (TSHR-KO) mice can ameliorate the hypothyroid state for an extended period. ES cells derived from heterozygous TSHR-KO blastocysts were stably transfected with Nkx2-1-GFP and Pax8-mcherry constructs and purified into 91.8% double positive cells by flow cytometry. After 5 days of activin A treatment these double positive cells were then induced to differentiate into neo-follicles in Matrigel for 21 days in the presence of 500μU/mL of TSH. Differentiated TFS expressing thyroglobulin mRNA were implanted under the kidney capsule of 4-6 weeks old TSHR-KO mice (n=5) as well as hind limb muscle (n=2) and anterior chamber of one eye (n=2). Five of the mice tested after 4 weeks were all rendered euthyroid and all mice remained euthyroid at 20 weeks post implantation. The serum T4 fully recovered (pre-bleed 0.62 ± 0.03 to 8.40 ± 0.57 µg/dL) and the previously elevated TSH became normal or suppressed (pre-bleed 391 ± 7.6 to 4.34 ± 1.25 ng/dL) at the end of the 20 week observation period. The final histology obtained from the implanted kidney tissues showed only rudimentary thyroid follicular structures but which stained positive for thyroglobulin expression. The presence of only rudimentary structures at the site of implant on these extended animals suggested possible migration of cells from the site of implant or an inability of TFCs to maintain proper follicular morphology in these external sites for extended periods. However, there were no signs of tumor formation and no immune infiltration. These preliminary studies show that TSHR-KO mice are a useful model for orthotropic implantation of functional thyroid cells without the need for thyroidectomy, radioiodine ablation or anti thyroid drug control of thyroid function. This approach is also proof of principle that thyroid cells derived from mouse ES cells are capable of surviving as functional neo-follicles in vivo for an extended period of 20 weeks.

Transplantation of Islets of Langerhans into the Anterior Chamber of the Eye for Longitudinal In Vivo Imaging

Noninvasive in vivo imaging techniques are attractive tools to longitudinally study various aspects of islet of Langerhans physiology and pathophysiology. Unfortunately, most imaging modalities currently applicable for clinical use do not allow the comprehensive investigation of islet cell biology due to limitations in resolution and/or sensitivity, while high-resolution imaging technologies like laser scanning microscopy (LSM) lack the penetration depth to assess islets of Langerhans within the pancreas. Significant progress in this area was made by the combination of LSM with the anterior chamber of the mouse eye platform, utilizing the cornea as a natural body window to study cell physiology of transplanted islets of Langerhans. We here describe the transplantation and longitudinal in vivo imaging of islets of Langerhans in the anterior chamber of the mouse eye as a versatile tool to study different features of islet physiology in health and disease.

Metabolic and Functional Heterogeneity in Pancreatic β Cells

Metabolic and secretory heterogeneity are fundamental properties of pancreatic islet β cells. Emerging data suggest that stable differences in the transcriptome and proteome of individual cells may create cellular hierarchies, which, in turn, establish coordinated functional networks. These networks appear to govern the secretory activity of the whole islet and be affected in some forms of diabetes mellitus. Functional imaging, for example, of intracellular calcium dynamics, has led to the demonstration of "small worlds" behavior, and the identification of highly connected "hub" (or "leader") cells and of follower populations subservient to them. Subsequent inactivation of members of either population, for example, using optogenetic approaches or photoablation, has confirmed the importance of hub cells as possible pacemakers. Hub cells appear to be enriched for the glucose phosphorylating enzyme glucokinase and for genes encoding other enzymes involved in glucose metabolism compared to follower cells. Recent findings have shown the relevance of cellular hierarchy in islets from multiple species including human, mouse and fish, and shown that it is preserved in vivo in the context of the fully vascularized and innervated islet. Importantly, connectivity is impaired by insults, which mimic the diabetic milieu, including high glucose and/or fatty levels, and by the ablation of genes associated with type 2 diabetes risk in genome-wide association studies. We discuss here the evidence for the existence of these networks and their failure in disease settings. We also briefly survey the challenges in understanding their properties.

In vivo imaging of type 1 diabetes immunopathology using eye-transplanted islets in NOD mice

AIMS/HYPOTHESIS

Autoimmune attack against the insulin-producing beta cells in the pancreatic islets results in type 1 diabetes. However, despite considerable research, details of the type 1 diabetes immunopathology in situ are not fully understood mainly because of difficult access to the pancreatic islets in vivo.

METHODS

Here, we used direct non-invasive confocal imaging of islets transplanted in the anterior chamber of the eye (ACE) to investigate the anti-islet autoimmunity in NOD mice before, during and after diabetes onset. ACE-transplanted islets allowed longitudinal studies of the autoimmune attack against islets and revealed the infiltration kinetics and in situ motility dynamics of fluorescence-labelled autoreactive T cells during diabetes development. Ex vivo immunostaining was also used to compare immune cell infiltrations into islet grafts in the eye and kidney as well as in pancreatic islets of the same diabetic NOD mice.

RESULTS

We found similar immune infiltration in native pancreatic and ACE-transplanted islets, which established the ACE-transplanted islets as reliable reporters of the autoimmune response. Longitudinal studies in ACE-transplanted islets identified in vivo hallmarks of islet inflammation that concurred with early immune infiltration of the islets and preceded their collapse and hyperglycaemia onset. A model incorporating data on ACE-transplanted islet degranulation and swelling allowed early prediction of the autoimmune attack in the pancreas and prompted treatments to intercept type 1 diabetes.

CONCLUSIONS/INTERPRETATION

The current findings highlight the value of ACE-transplanted islets in studying early type 1 diabetes pathogenesis in vivo and underscore the need for timely intervention to halt disease progression.

A Versatile, Portable Intravital Microscopy Platform for Studying Beta-cell Biology In Vivo

The pancreatic islet is a complex micro-organ containing numerous cell types, including endocrine, immune, and endothelial cells. The communication of these systems is lost upon isolation of the islets, and therefore the pathogenesis of diabetes can only be fully understood by studying this organized, multicellular environment in vivo. We have developed several adaptable tools to create a versatile platform to interrogate β-cell function in vivo. Specifically, we developed β-cell-selective virally-encoded fluorescent protein biosensors that can be rapidly and easily introduced into any mouse. We then coupled the use of these biosensors with intravital microscopy, a powerful tool that can be used to collect cellular and subcellular data from living tissues. Together, these approaches allowed the observation of in vivo β-cell-specific ROS dynamics using the Grx1-roGFP2 biosensor and calcium signaling using the GcAMP6s biosensor. Next, we utilized abdominal imaging windows (AIW) to extend our in vivo observations beyond single-point terminal measurements to collect longitudinal physiological and biosensor data through repeated imaging of the same mice over time. This platform represents a significant advancement in our ability to study β-cell structure and signaling in vivo, and its portability for use in virtually any mouse model will enable meaningful studies of β-cell physiology in the endogenous islet niche.

The eye as a novel imaging site in diabetes research

Diabetes develops due to deficient functional β cell mass, insulin resistance, or both. Yet, various challenges in understanding the mechanisms underlying diabetes development in vivo remain to be overcome owing to the lack of appropriate intravital imaging technologies. To meet these challenges, we have exploited the anterior chamber of the eye (ACE) as a novel imaging site to understand diabetes basics and clinics in vivo. We have developed a technology platform transplanting pancreatic islets into the ACE where they later on can be imaged non-invasively for long time. It turns out that the ACE serves as an optimal imaging site and provides implanted islets with an oxygen-rich milieu and an immune-privileged niche where they undergo optimal engraftment, rich vascularization and dense innervation, preserve organotypic features and live with satisfactory viability and functionality. The ACE technology has led to a series of significant observations. It enables in vivo microscopy of islet cytoarchitecture, function and viability in the physiological context and intravital imaging of a variety of pathological events such as autoimmune insulitis, defects in β cell function and mass and insulin resistance during diabetes development in a real-time manner. Furthermore, application of the ACE technology in humanized mice and non-human primates verifies translational and clinical values of the technology. In this article, we describe the ACE technology in detail, review accumulated knowledge gained by means of the ACE technology and delineate prospective avenues for the ACE technology.

Magnetic particle imaging of islet transplantation in the liver and under the kidney capsule in mouse models

Background

Islet transplantation (Tx) represents the most promising therapy to restore normoglycemia in type 1 diabetes (T1D) patients to date. As significant islet loss has been observed after the procedure, there is an urgent need for developing strategies for monitoring transplanted islet grafts. In this report we describe for the first time the application of magnetic particle imaging (MPI) for monitoring transplanted islets in the liver and under the kidney capsule in experimental animals.

Methods

Pancreatic islets isolated from Papio hamadryas were labeled with superparamagnetic iron oxides (SPIOs) and used for either islet phantoms or Tx in the liver or under the kidney capsule of NOD scid mice. MPI was used to image and quantify islet phantoms and islet transplanted experimental animals post-mortem at 1 and 14 days after Tx. Magnetic resonance imaging (MRI) was used to confirm the presence of labeled islets in the liver and under the kidney capsule 1 day after Tx.

Results

MPI of labeled islet phantoms confirmed linear correlation between the number of islets and the MPI signal (R²=0.988). Post-mortem MPI performed on day 1 after Tx showed high signal contrast in the liver and under the kidney capsule. Quantitation of the signal supports islet loss over time, which is normally observed 2 weeks after Tx. No MPI signal was observed in control animals. In vivo MRI confirmed the presence of labeled islets/islet clusters in liver parenchyma and under the kidney capsule one day after Tx.

Conclusions

Here we demonstrate that MPI can be used for quantitative detection of labeled pancreatic islets in the liver and under the kidney capsule of experimental animals. We believe that MPI, a modality with no depth attenuation and zero background tissue signal could be a suitable method for imaging transplanted islet grafts.

Single synchronous delivery of FK506-loaded polymeric microspheres with pancreatic islets for the successful treatment of streptozocin-induced diabetes in mice

Immune rejection after transplantation is common, which leads to prompt failure of the graft. Therefore, to prolong the survival time of the graft, immunosuppressive therapy is the norm. Here, we report a robust immune protection protocol using FK506-loaded microspheres (FK506M) in injectable hydrogel. Pancreatic islets were codelivered with the FK506M into the subcutaneous space of streptozocin-induced diabetic mice. The islets codelivered with 10 mg/kg FK506M maintained normal blood glucose levels during the study period (survival rate: 60%). However, transplantation of islets and FK506M at different sites hardly controlled the blood glucose level (survival rate: 20%). Immunohistochemical analysis revealed an intact morphology of the islets transplanted with FK506M. In addition, minimal number of immune cells invaded inside the gel of the islet-FK506M group. The single injection of FK506M into the local microenvironment effectively inhibited immune rejection and prolonged the survival time of transplanted islets in a xenograft model.

Intraocular in vivo imaging of pancreatic islet cell physiology/pathology

BACKGROUND

Diabetes mellitus has reached epidemic proportions and requires new strategies for treatment. Unfortunately, the efficacy of treatment regimens on maintaining/re-gaining functional beta cell mass can, at the present, only be determined indirectly. Direct monitoring of beta cell mass is complicated by the anatomy of the endocrine pancreas, which consists of thousands to a million of discrete micro-organs, i.e. islets of Langerhans, which are scattered throughout the pancreas.

SCOPE OF REVIEW

Here, we review the progress made over the last years using the anterior chamber of the eye as a transplantation site for functional imaging of pancreatic islet cells in the living organism. Islets engrafted on the iris are vascularized and innervated and the cornea, serving as a natural body-window, allows for microscopic, non-invasive, longitudinal evaluation of islet/beta cell function and survival with single-cell resolution in health and disease.

MAJOR CONCLUSIONS

Data provided by us and others demonstrate the high versatility of this imaging platform. The use of 'reporter islets' engrafted in the eye, reporting on the status of in situ endogenous islets in the pancreas of the same animal, allows the identification of key-events in the development and progression of diabetes. This will not only serve as a versatile research tool but will also lay the foundation for a personalized medicine approach and will serve as a screening platform for new drugs and/or treatment protocols. 'Metabolic' islet transplantation, in which islets engrafted in the eye replace the endogenous beta cells, will allow for the establishment of islet-specific transgenic models and 'humanized' mouse models as well as serving as the basis for a new clinical transplantation site for the cure of diabetes.