Pancreatic Pseudoislets: An Organoid Archetype for Metabolism Research.

Pancreatic islets are vital endocrine regulators of systemic metabolism, and recent investigations have increasingly focused on understanding human islet biology. Studies of isolated human islets have advanced understanding of the development, function, and regulation of cells comprising islets, especially pancreatic α- and ß-cells. However, the multicellularity of the intact islet has stymied specific experimental approaches-particularly in genetics and cell signaling interrogation. This barrier has been circumvented by the observation that islet cells can survive dispersion and reaggregate to form "pseudoislets," organoids that retain crucial physiological functions, including regulated insulin and glucagon secretion. Recently, exciting advances in the use of pseudoislets for genetics, genomics, islet cell transplantation, and studies of intraislet signaling and islet cell interactions have been reported by investigators worldwide. Here we review molecular and cellular mechanisms thought to promote islet cell reaggregation, summarize methods that optimize pseudoislet development, and detail recent insights about human islet biology from genetic and transplantation-based pseudoislet experiments. Owing to robust, international programs for procuring primary human pancreata, pseudoislets should serve as both a durable paradigm for primary organoid studies and as an engine of discovery for islet biology, diabetes, and metabolism research.

CRISPR-based genome editing in primary human pancreatic islet cells.

Gene targeting studies in primary human islets could advance our understanding of mechanisms driving diabetes pathogenesis. Here, we demonstrate successful genome editing in primary human islets using clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9). CRISPR-based targeting efficiently mutated protein-coding exons, resulting in acute loss of islet ß-cell regulators, like the transcription factor PDX1 and the KATP channel subunit KIR6.2, accompanied by impaired ß-cell regulation and function. CRISPR targeting of non-coding DNA harboring type 2 diabetes (T2D) risk variants revealed changes in ABCC8, SIX2 and SIX3 expression, and impaired ß-cell function, thereby linking regulatory elements in these target genes to T2D genetic susceptibility. Advances here establish a paradigm for genetic studies in human islet cells, and reveal regulatory and genetic mechanisms linking non-coding variants to human diabetes risk.

SIX2 and SIX3 coordinately regulate functional maturity and fate of human pancreatic ß cells.

The physiological functions of many vital tissues and organs continue to mature after birth, but the genetic mechanisms governing this postnatal maturation remain an unsolved mystery. Human pancreatic ß cells produce and secrete insulin in response to physiological cues like glucose, and these hallmark functions improve in the years after birth. This coincides with expression of the transcription factors SIX2 and SIX3, whose functions in native human ß cells remain unknown. Here, we show that shRNA-mediated SIX2 or SIX3 suppression in human pancreatic adult islets impairs insulin secretion. However, transcriptome studies revealed that SIX2 and SIX3 regulate distinct targets. Loss of SIX2 markedly impaired expression of genes governing ß-cell insulin processing and output, glucose sensing, and electrophysiology, while SIX3 loss led to inappropriate expression of genes normally expressed in fetal ß cells, adult α cells, and other non-ß cells. Chromatin accessibility studies identified genes directly regulated by SIX2. Moreover, ß cells from diabetic humans with impaired insulin secretion also had reduced SIX2 transcript levels. Revealing how SIX2 and SIX3 govern functional maturation and maintain developmental fate in native human ß cells should advance ß-cell replacement and other therapeutic strategies for diabetes.

Aquagenic pruritus in an adolescent effectively managed with ß-alanine supplementation.

Aquagenic pruritus is a rare debilitating condition, which can be idiopathic, iatrogenic, or associated with systemic disease. In idiopathic cases, treatment can be challenging as options are limited and of variable efficacy. Here, we report the case of a teenage boy with refractory idiopathic aquagenic pruritus effectively managed with administration of ß-alanine supplementation, a treatment gaining traction in lay media but not yet reported in the medical literature. This report adds to the limited options published for treatment of idiopathic aquagenic pruritus in pediatric patients.

The long dystrophin gene product Dp427 modulates retinal function and vascular morphology in response to age and retinal ischemia.

Mutations in dystrophin are the major cause of muscular dystrophies. Continuous muscular degeneration and late stage complications, including cardiomyopathy and respiratory insufficiency, dominate the clinical phenotype. Gene expression and regulation of the dystrophin gene outside of muscular tissue is far more complex. Multiple tissue-specific dystrophin gene products are widely expressed throughout the body, including the central nervous system and eye, predisposing affected patients to secondary complications in non-muscular tissues. In this study, we evaluated the impact of the full-length dystrophin gene product, Dp427, on retinal homeostasis and angiogenesis. Based on the clinical case of a Duchenne muscular dystrophy (DMD) patient who developed severe fibrovascular changes in the retina in response to hypoxic stress, we hypothesized that defects in Dp427 make the retina more susceptible to stresses such as ageing and ischemia. To further study this, a mouse strain lacking Dp427 expression (Mdx) was studied during retinal development, ageing and in the oxygen-induced retinopathy (OIR) model. While retinal vascular morphology was normal during development and ageing, retinal function measured by electroretinography (ERG) was slightly reduced in young adult Mdx mice and deteriorated with age. Mdx mice also had increased retinal neovascularization in response to OIR and more pronounced long-term deterioration in retinal function following OIR. Based on these results, we suggest that DMD patients with a mutation in Dp427 may experience disturbed retinal homeostasis with increasing age and therefore be prone to develop excessive retinal neovascular changes in response to hypoxic stress. DMD patients in late disease stages should, thus, be regularly examined to detect asymptomatic retinal abnormalities and prevent visual impairment.

Hypoxia-induced metabolic stress in retinal pigment epithelial cells is sufficient to induce photoreceptor degeneration.

Photoreceptors are the most numerous and metabolically demanding cells in the retina. Their primary nutrient source is the choriocapillaris, and both the choriocapillaris and photoreceptors require trophic and functional support from retinal pigment epithelium (RPE) cells. Defects in RPE, photoreceptors, and the choriocapillaris are characteristic of age-related macular degeneration (AMD), a common vision-threatening disease. RPE dysfunction or death is a primary event in AMD, but the combination(s) of cellular stresses that affect the function and survival of RPE are incompletely understood. Here, using mouse models in which hypoxia can be genetically triggered in RPE, we show that hypoxia-induced metabolic stress alone leads to photoreceptor atrophy. Glucose and lipid metabolism are radically altered in hypoxic RPE cells; these changes impact nutrient availability for the sensory retina and promote progressive photoreceptor degeneration. Understanding the molecular pathways that control these responses may provide important clues about AMD pathogenesis and inform future therapies.

Neurovascular crosstalk between interneurons and capillaries is required for vision.

Functional interactions between neurons, vasculature, and glia within neurovascular units are critical for maintenance of the retina and other CNS tissues. For example, the architecture of the neurosensory retina is a highly organized structure with alternating layers of neurons and blood vessels that match the metabolic demand of neuronal activity with an appropriate supply of oxygen within perfused blood. Here, using murine genetic models and cell ablation strategies, we have demonstrated that a subset of retinal interneurons, the amacrine and horizontal cells, form neurovascular units with capillaries in 2 of the 3 retinal vascular plexuses. Moreover, we determined that these cells are required for generating and maintaining the intraretinal vasculature through precise regulation of hypoxia-inducible and proangiogenic factors, and that amacrine and horizontal cell dysfunction induces alterations to the intraretinal vasculature and substantial visual deficits. These findings demonstrate that specific retinal interneurons and the intraretinal vasculature are highly interdependent, and loss of either or both elicits profound effects on photoreceptor survival and function.

Choroid sprouting assay: an ex vivo model of microvascular angiogenesis.

Angiogenesis of the microvasculature is central to the etiology of many diseases including proliferative retinopathy, age-related macular degeneration and cancer. A mouse model of microvascular angiogenesis would be very valuable and enable access to a wide range of genetically manipulated tissues that closely approximate small blood vessel growth in vivo. Vascular endothelial cells cultured in vitro are widely used, however, isolating pure vascular murine endothelial cells is technically challenging. A microvascular mouse explant model that is robust, quantitative and can be reproduced without difficulty would overcome these limitations. Here we characterized and optimized for reproducibility an organotypic microvascular angiogenesis mouse and rat model from the choroid, a microvascular bed in the posterior of eye. The choroidal tissues from C57BL/6J and 129S6/SvEvTac mice and Sprague Dawley rats were isolated and incubated in Matrigel. Vascular sprouting was comparable between choroid samples obtained from different animals of the same genetic background. The sprouting area, normalized to controls, was highly reproducible between independent experiments. We developed a semi-automated macro in ImageJ software to allow for more efficient quantification of sprouting area. Isolated choroid explants responded to manipulation of the external environment while maintaining the local interactions of endothelial cells with neighboring cells, including pericytes and macrophages as evidenced by immunohistochemistry and fluorescence-activated cell sorting (FACS) analysis. This reproducible ex vivo angiogenesis assay can be used to evaluate angiogenic potential of pharmacologic compounds on microvessels and can take advantage of genetically manipulated mouse tissue for microvascular disease research.