In response to the lockdowns and travel bans during the coronavirus disease 2019 pandemic, Peter C. Butler at the University of California, Los Angeles (UCLA), started a virtual islet biology seminar series. After the authors of this article joined him as co-organizers, this initiative became the Islet Research Seminar Series (IRSS). Like islets of Langerhans adapt to their changing environment, the islet biology community quickly embraced this new format. The IRSS evolved into a lasting scientific forum that convenes weekly and is attended by islet biologists from the U.S., Canada, Europe, and Israel. The series covers a range of topics in islet biology, with presentations from scientists representing all career stages. It has proven particularly valuable for trainees and early-stage investigators in exposing them to a variety of topics in islet biology without travel required and facilitating more spontaneous interactions with senior scientists than at in-person meetings. While the online format is not meant to replace live scientific conferences, we believe that the IRSS plays a unique role in keeping the islet biology community connected and abreast of the most recent scientific discoveries in our field. The success of this platform stands as a testament to the scientific community to adapt and thrive through challenges. This article is dedicated to Peter C. Butler, UCLA, who initiated the IRSS.

GLP-1 receptor agonists have emerged as key pharmacological tools in the treatment of type 2 diabetes and obesity. While their anorexigenic effects are well characterized, the mechanisms by which GLP-1 modulates pancreatic β-cell function remain only partially understood. In this article, we argue that GLP-1 receptor agonists should be viewed as integrative regulators of β-cell function and explore the multifaceted actions of GLP-1 analogs on β-cell signaling. GLP-1 influences key secretagogues and intracellular mediators (calcium, glutamate, γ-aminobutyric acid, serotonin, and urocortin-3), with complex roles in insulin exocytosis. Additionally, we discuss the interplay between calcium and cAMP, and how GLP-1 modulates both pathways to coordinate insulin secretion. Emerging evidence suggests that GLP-1 analogs affect mitochondrial morphology and redox homeostasis. Considering the relatively low expression of classical antioxidant enzymes in β-cells, and their reliance on both glycolytic and mitochondrial metabolism to sustain insulin secretion, the influence of GLP-1 on mitochondrial dynamics and reactive oxygen species may play a central role in sustaining cell function and viability. Despite recent advances, critical gaps persist in the literature, particularly regarding organelle cross talk, intracellular calcium stores, and the modulation of vesicular content. Drawing on current evidence, we propose that three mechanistic dimensions (intracellular neurotransmitters, mitochondrial remodeling, and redox control) represent key areas where clarifying GLP-1 actions could most effectively advance the field. Further investigation into these mechanisms is essential for a comprehensive understanding of GLP-1 actions in β-cells. This knowledge may help refine current incretin-based therapies and identify novel molecular targets for the treatment of metabolic disorders.

Indirect calorimetry determines energy expenditure by measuring respiratory gas exchange. The approach is based on the principle that nutrient metabolism consumes O2 and produces CO2 and water in predictable ratios that can be compared with heat production. Due to the impracticality and high cost of direct calorimetry, indirect calorimetry is the major approach for modern metabolic studies in preclinical models. Despite the broad adoption of this method in rodent phenotyping, the field has lacked standardized methods for analyzing, representing, and sharing these data, limiting scientific progress. The recent review in Nature Metabolism by the International Indirect Calorimetry Consensus Committee (IICCC) addresses the lack of standardized methods by providing updated guidelines for data processing and representation and emphasizes the importance of shared data repositories tailored to these studies. These expert consensus standards aim to improve transparency, facilitate data sharing and archiving, and enhance cross-study comparability. We encourage authors submitting to Diabetes to adopt the IICCC guidelines to strengthen rigor and reproducibility in the field.

Atherosclerotic cardiovascular disease (ASCVD) risk begins increasing years before the clinical onset of type 2 diabetes, driven in part by ectopic lipid accumulation. Many individuals predisposed to diabetes often gain weight rapidly and have limited capacity to expand subcutaneous fat, leading to central fat storage and ectopic lipid deposition-especially in the liver. Hepatic fat contributes to metabolic dysfunction and elevated triglyceride-rich lipoproteins (TRLs), which are atherogenic. Alongside higher blood pressure, these factors accelerate atherosclerosis even before hyperglycemia is evident. Although traditional cardiovascular risk factors like LDL cholesterol (LDL-C) and smoking have declined, rising obesity-particularly among younger individuals-is shifting ASCVD risk more toward pathways linked to ectopic lipid accumulation and prolonged exposure to diabetes-related metabolic disturbances. Ethnic variation plays a significant role in modifying this risk. South Asians, for example, develop type 2 diabetes at lower BMIs and tend to have higher hepatic fat and TRL levels than White individuals, contributing to their increased ASCVD burden. Conversely, people of African ancestry often have lower hepatic fat and TRL levels at similar BMIs, correlating with lower ASCVD risk despite elevated diabetes risk. Risk profiles in other ethnic groups remain understudied. These findings highlight the need for early obesity prevention and ethnically tailored strategies for ASCVD risk assessment and management. Without targeted interventions, rising global rates of obesity and type 2 diabetes, especially in low- and middle-income countries, will increase ectopic lipid accumulation, TRLs, and blood pressure, ultimately accelerating ASCVD progression and reversing prior gains made in cardiovascular prevention.

There is significant evidence that acute stress, a challenge to an organism's homeostasis, has dramatic effects on metabolic control. Acute stress impairs blood glucose control in people with both type 1 and type 2 diabetes. In addition, growing evidence suggests that metabolic responses to stress in people without diabetes may be a crucial determinant of health. Acute dysregulation of blood glucose in the hospital setting, including both hyper- and hypoglycemia, predicts short- and long-term morbidity and mortality in patients with critical illnesses. Animal studies indicate that exposure to physiological and psychological stressors activates a highly conserved network of neural circuits that ultimately coordinate the functions of multiple organs to increase blood glucose. In this article, we provide an overview of the neural populations and circuits that increase blood glucose in response to acute stress, including our research funded by the American Diabetes Association Pathway to Stop Diabetes program, highlighting the impacts on clinical outcomes and opportunities for the development of therapies for diabetes. This article is part of a series of perspectives that report on research funded by the American Diabetes Association Pathway to Stop Diabetes program.

Diabetes currently affects ∼37 million adults in the U.S. and 537 million people worldwide, with type 2 diabetes (T2D) accounting for 90%-95% of the diabetes burden. The transition from normal glucose regulation (NGR) to T2D is via an intermediate stage of prediabetes, characterized by impaired fasting glucose (IFG) and impaired glucose tolerance (IGT). Prediabetes affects ∼98 million adults in the U.S.; worldwide, more than 541 million adults have IGT and 319 million adults have IFG. Prediabetes is associated with increased risks of developing vascular and neuropathic complications, besides the risk of progression to T2D. Discussed herein are the demographic, anthropometric, biobehavioral, biochemical, and molecular factors associated with the transition from NGR to prediabetes. The natural history of prediabetes predicts time-dependent progression to T2D, as sustained recovery from prediabetes is uncommon without intervention. Lifestyle modification and certain medications interrupt the progression to T2D and may restore NGR. The landmark intervention trials are discussed, with an interpretive focus on their limitations and the need for novel approaches for durable reversal of prediabetes.

Following the trends of the adult obesity epidemic, and worsened by school disruptions during the coronavirus disease 2019 pandemic, childhood obesity prevalence has reached unprecedented levels. The health implications for this generation are especially concerning, as childhood-onset obesity has more severe health consequences than weight gain that begins in adulthood, including increased risk of type 2 diabetes and diabetes-related complications. The complexity of obesity treatment has been challenging, including remarkable heterogeneity in obesity phenotypes and treatment responses among both adults and children. Many in the field have therefore highlighted a need for precision medicine approaches in obesity treatment across age-groups. This includes a need for precision risk stratification to better target treatment intensity, which will require a better understanding of the earliest stages of metabolic syndrome pathophysiology. The health, function, and distribution of adipose tissue have been established as important determinants of metabolic health in both childhood- and adult-onset obesity, making adipose tissue a promising target for understanding phenotypic heterogeneity in obesity. Here, we provide a brief overview of the current limited understanding of adipose tissue biology during childhood development and discuss opportunities for further research into adipose-centric precision medicine approaches in childhood-onset obesity and type 2 diabetes.

Diabetes triggers cell-type-specific responses in the retina, leading to vascular lesions, glial dysfunction, and neurodegeneration, all of which contribute to the progression of diabetic retinopathy (DR). However, the specific cell types involved in disease development and the molecular mechanisms driving their responses have not yet been fully clarified, impeding the creation of effective therapeutic strategies. Recent advancements in single-cell or single-nuclei transcriptomic technologies have provided a systematic approach to profile transcript-level alterations at single-cell resolution, allowing for an in-depth analysis of diabetes-induced retinal transcriptional changes across various animal models for DR. Here, in the context of research funded by the American Diabetes Association Pathway to Stop Diabetes program, we discuss the cell-type-specific responses in the neural retina identified through single-cell transcriptomic analyses. We emphasize new insights into neural retinal responses, potential therapeutic targets, and the limitations and unresolved topics that warrant further investigation. This article is part of a series of perspectives that report on research funded by the American Diabetes Association Pathway to Stop Diabetes program.

This article summarizes the current understanding of the heterogeneity of type 1 diabetes from a June 2024 international Expert Forum organized by the editors of Diabetes, Diabetes Care, and Diabetologia. The Forum reviewed key factors contributing to the development and progression of type 1 diabetes and outlined specific, high-priority research questions. Knowledge gaps were identified, and, notably, opportunities to harness disease heterogeneity to develop personalized therapies were outlined. Herein, we summarize our discussions and review the heterogeneity of genetic risk and immunologic and metabolic phenotypes that influence and characterize type 1 diabetes progression (presented as a palette of risk factors). We discuss how these age-related factors determine disease aggressiveness (along gradients) and describe how variable immunogenetic pathways aggregate (into networks) to affect β-cell and other pancreatic pathologies to cause clinical disease at different ages and with variable severity (described as disease-related thresholds). Heterogeneity of pathogenesis and clinical severity opens avenues to prevention and intervention, including the potential of disease-modifying immunotherapy and islet cell replacement. We conclude with a call for 1) continued research to identify more factors contributing to the disease, both overall and in specific subgroups; 2) investigations focusing on both individuals who surpass metabolic and immune thresholds and develop diabetes and those who remain disease free with the same level of immunogenetic risk; and 3) efforts to identify where the current type 1 diabetes staging system may fall short and determine how it can be improved to capture and leverage heterogeneity in prevention and intervention strategies.

There is currently a revolution in the pharmacologic treatment of obesity and diabetes with newly available agonists of incretin receptors. The health benefits of these novel treatments include not only metabolic effects but also improvements in brain neurodegenerative conditions. Receptors for incretins have been described in the hypothalamic appetite regulatory center; however, their expression in the peripheral nervous system (PNS) has been largely overlooked, despite likely contributing important effects. For example, the PNS is essential for the control of numerous metabolically relevant pathways in tissues such as liver, adipose, intestine, and muscle, and incretin receptors are found on nerves innervating some, if not all, of these metabolically important tissues. In this article, we summarize the knowledge to date regarding incretin receptors and incretin drug actions in the PNS, as well as PNS control over incretin release, and the related implications for metabolic disease states that are accompanied by peripheral neuropathy.

Until recently, the prevalence of endogenous Cushing syndrome has been considered to be low. However, improved diagnostic strategies and increased awareness have broadened our understanding of hypercortisolism and its role in the pathophysiology of type 2 diabetes, obesity, hypertension, and cardiovascular disease. Recent studies from Europe, South America, and the U.S. have demonstrated that a significant percentage of individuals with difficult-to-control type 2 diabetes, despite treatment with multiple glucose-lowering agents, have hypercortisolism as a causative factor in their poorly managed diabetes. In this review, we examine the pathophysiologic mechanisms via which excess cortisol contributes to the impairment in glucose homeostasis and recommend that hypercortisolism be added to the Ominous Octet to form the Noxious Nine as the pathophysiologic foundation for the development of type 2 diabetes.

Current research and development are ushering in a new era of novel islet β-cell replacement therapies that can no longer be considered solely a rescue treatment for those with unstable glucose management. Clinical trial design must ensure that the application of islet β-cell replacement is broadened beyond the indication of severe hypoglycemia given the potential for establishing insulin-independent normoglycemia. It is imperative that people with type 1 diabetes and their clinicians are at the center of the risk-benefit equipoise as evidence for the safety of cellular products, transplant sites, and immune protection strategies accumulates and an increasing number of options for intervention become available.

The dorsal raphe nucleus (DRN) is a key regulator of food intake and body weight. The DRN has historically been associated with feeding, as it houses the single largest population of serotonergic neurons in the mammalian brain. Few studies have demonstrated a direct role for DRN serotonergic neurons in regulating feeding; none of these studies have demonstrated effects near those elicited by serotonin, itself. There are many nonserotonergic cell types in the DRN that play an integral role in feeding. These DRN cell types play important roles in both hunger and satiation.

Sarcopenic obesity, a subtype of obesity, is marked by reduced skeletal muscle mass and function, or sarcopenia, and poses a significant health challenge to older adults as it affects an estimated 28.3% of people aged >60 years. This subtype is unique to older adults as aging exacerbates sarcopenia and obesity due to changes in energy metabolism, hormones and inflammatory markers, and lifestyle factors. Traditional treatments for sarcopenic obesity have been focused on exercise and dietary modifications to reduce fat while maintaining muscle mass. Newer glucagon-like peptide 1 receptor agonists (GLP-1RAs) and dual gastric inhibitory polypeptide/GLP-1 receptor agonists (GIP/GLP-1RAs), including liraglutide, semaglutide, and tirzepatide, have shown great promise to reduce weight, treat obesity-related complications, improve physical function, and improve quality of life, in younger clinical trial populations. However, the use of GLP-1RAs and GIP/GLP-1RAs has not been exhaustively evaluated in older adults with sarcopenic obesity. These medications come with the risk of loss of muscle mass and an increased rate of adverse events. Thus, clinicians should use them cautiously by weighing the potential benefits against their risks. Herein, we discuss a possible approach to using GLP-1RAs and GIP/GLP-1RAs in patients with sarcopenic obesity, including considerations for patient identification, monitoring, maintenance, and discontinuation. In this article we also discuss the emerging treatments that will be available, which may include activin type II receptor antibodies and selective androgen receptor agonists. We conclude by highlighting the advancement of geroscience as a promising field for individualizing treatments in the future.

Treatment responses to behavioral, surgical, and pharmacological approaches in obesity are highly variable in quantity and quality. Here we refer to high-quality weight loss as a high proportion of fat to skeletal muscle mass lost. Given the role of skeletal muscle in energy expenditure, glucose homeostasis, metabolic flexibility, mobility, and strength, excessive loss of skeletal muscle during weight loss is a concern for overall health. Challenges in accurately measuring body composition, especially skeletal muscle, limit our understanding of muscle loss during obesity treatment. Recent incretin-related pharmacotherapies improve muscle metabolic health by enhancing glucose uptake and reducing muscle lipids but, like other weight loss interventions, are associated with muscle loss. Newer pharmacological interventions are being developed to minimize muscle loss, but many questions remain. This article examines the metabolic importance of skeletal muscle and its measurement clinically, as well as key genetic and metabolic factors influencing skeletal muscle and the quality of weight loss. Genetics can affect muscle composition (e.g., fiber types) and function. Together with metabolic factors, including neurohormonal responses and skeletal muscle metabolic efficiency and adaptation, there is variability in weight loss outcomes. In future research investigators should continue to focus on factors affecting skeletal muscle and on personalized strategies to optimize weight loss quality preserving the physical and metabolic functions of skeletal muscle.

The primary treatment for obesity involves calorie restriction (CR) to promote dietary weight loss achieved through interventions including behavioral modification, bariatric surgery, and antiobesity medications. In adults with obesity, CR-induced weight loss enhances physical function and improves quality of life, while also reducing the burden of various obesity-related chronic conditions, including hypertension, diabetes, obstructive sleep apnea, and atherosclerotic heart disease. However, it is also associated with a decline in lean mass and bone mineral density, which increases the risk of sarcopenia and osteoporosis. When performed alongside CR, progressive resistance training (RT) attenuates this loss of lean mass and bone mass, while the addition of aerobic training (AT) further improves cardiorespiratory fitness. The individual benefits of RT and AT are complementary, and combining both exercise training modalities during CR provides the most optimal benefits for body composition and physical function. The World Health Organization recommends that adults engage in at least 150 min of moderate-intensity or 75 min of vigorous-intensity AT weekly and participate in RT activities involving major muscle groups at least 2 days per week. While this recommendation applies to the general adult population, regular exercise training that incorporates both RT and AT is particularly crucial for adults with obesity undergoing weight loss interventions. This clinical perspective highlights the benefits of exercise training alongside current weight loss strategies, such as lifestyle changes, bariatric surgery, and pharmacotherapy, with a focus on incretin-based therapies.

In combatting the obesity crisis, leveraging mechanisms that lower body weight is critical. The finding that treatment with tirzepatide, a glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) receptor agonist, produces profound weight loss highlights the value of activating the incretin receptors. Supporting this, recent studies have revealed mechanisms by which GIP receptor (GIPR) activation is beneficial in pancreatic islets, the central nervous system (CNS), and adipose tissue. Paradoxically, a hypothesis has emerged that GIPR antagonism could be an additional option in treating obesity. This concept stems from concern that GIP facilitates lipid uptake and storage in adipose tissue, although the lipid-buffering capacity of adipocytes versus other cell types is metabolically favorable. In this article, we highlight the natural physiology of the incretins, noting GIP as the primary incretin. In the CNS, GIPR agonism attenuates nausea and suppresses appetite, features that also help GLP-1 receptor agonism promote a negative energy balance. Further, we provide rationale that, in protecting against ectopic fat distribution and augmenting substrate utilization to promote insulin sensitivity, GIPR activity in adipose tissue is advantageous. Collectively, these attributes support GIPR agonism in the treatment of obesity and metabolic disease.

Current and emerging strategies to therapeutically target weight management include pairing agonism of the glucagon-like peptide 1 receptor (GLP-1R) with either agonism or antagonism of the glucose-dependent insulinotropic polypeptide receptor (GIPR). On the surface, these two approaches seem contradictory, yet they have produced similar effects for weight loss in clinical studies. Arguments that support the rationale for both approaches are made in these point-counterpoint articles, founded on preclinical studies, human genetics, and clinical outcomes. Here, we attempt to reconcile how two opposing approaches can produce similar effects on body weight by evaluating the leading hypotheses derived from the available evidence.

Obesity is a prevalent disease that also contributes to the incidence and severity of many other chronic diseases and health conditions. Treatment approaches include lifestyle intervention, bariatric surgery, and pharmacological approaches, with glucagon-like peptide 1 (GLP-1) receptor agonists approved specifically for weight loss having changed the treatment landscape significantly in the last 5 years. Targeting the glucose-dependent insulinotropic polypeptide (GIP) receptor may enhance the metabolic benefits of GLP-1 receptor agonism. These beneficial effects are seen with both GIP receptor antagonism and GIP receptor agonism, although the mechanisms underlying this apparent paradox remain unknown. Here, we summarize the physiologic, genetic, and clinical evidence for pursuing GIP receptor antagonism to achieve metabolic and weight benefits. Both global and central nervous system knockout of GIP receptors protects mice fed a high-fat diet from obesity and insulin resistance. Genome-wide association studies in humans support this notion, correlating lower BMI with GIP receptor genetic variants with reduced function. Pharmacologic approaches in mice and monkeys confirm that GIP receptor antagonism enhances GLP-1-induced weight reduction and other metabolic benefits, and a phase 1 study provides proof of principle that beneficial effects extend to humans. GIP receptor antagonism may represent an important new mechanism to expand the treatment options available to individuals living with obesity.

Islet cell replacement therapies have evolved as a viable treatment option for type 1 diabetes complicated by problematic hypoglycemia and glycemic lability. Refinements of islet manufacturing, islet transplantation procedures, peritransplant recipient management, and immunosuppressive protocols allowed most recipients to achieve favorable outcomes. Subsequent phase 3 trials of transplantation of deceased donor islets documented the effectiveness of transplanted islets in restoring near-normoglycemia, glycemic stability, and protection from severe hypoglycemia, with an acceptable safety profile for the enrolled high-risk population. Health authorities in several countries have approved deceased donor islet transplantation for treating patients with type 1 diabetes and recurrent severe hypoglycemia. These achievements amplified academic and industry efforts to generate pluripotent stem cell-derived β-cells through directed differentiation for β-cell replacement. Preliminary results of ongoing clinical trials suggest that the transplantation of stem cell-derived β-cells can consistently restore insulin independence in immunosuppressed recipients with type 1 diabetes, thus signaling the profound progress made in generating an unlimited and a uniform supply of cells for transplant. Avoiding the risks of chronic immunosuppression represents the next frontier. Several strategies have entered or are approaching clinical investigation, including immune-isolating islets, engineering immune-privileged islet implantation sites, rendering islets immune evasive, and inducing immune tolerance in transplanted islets. Capitalizing on high-dimensional, multiomic technologies for deep profiling of graft-directed immunity and the fate of the graft will provide new insights that promise to translate into sustaining functional graft survival long-term. Leveraging these parallel progression paths will facilitate the wider clinical adoption of cell replacement therapies in diabetes care.