The occurrence of islet amyloid polypeptide amyloidosis in Japanese subjects

Role of β-cell autophagy in β-cell physiology and the development of diabetes

Elucidating the molecular mechanism of autophagy was a landmark in understanding not only the physiology of cells and tissues, but also the pathogenesis of diverse diseases, including diabetes and metabolic disorders. Autophagy of pancreatic β-cells plays a pivotal role in the maintenance of the mass, structure and function of β-cells, whose dysregulation can lead to abnormal metabolic profiles or diabetes. Modulators of autophagy are being developed to improve metabolic profile and β-cell function through the removal of harmful materials and rejuvenation of organelles, such as mitochondria and endoplasmic reticulum. Among the known antidiabetic drugs, glucagon-like peptide-1 receptor agonists enhance the autophagic activity of β-cells, which might contribute to the profound effects of glucagon-like peptide-1 receptor agonists on systemic metabolism. In this review, the results from studies on the role of autophagy in β-cells and their implication in the development of diabetes are discussed. In addition to non-selective (macro)autophagy, the role and mechanisms of selective autophagy and other minor forms of autophagy that might occur in β-cells are discussed. As β-cell failure is the ultimate cause of diabetes and unresponsiveness to conventional therapy, modulation of β-cell autophagy might represent a future antidiabetic treatment approach, particularly in patients who are not well managed with current antidiabetic therapy.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

Diversity of pathophysiology in type 2 diabetes shown by islet pathology

The etiology of type 2 diabetes is multifactorial, in which environmental and genetic factors are involved to varying degrees. This suggests that its pathophysiology might vary depending on the individuals. Knowledge of the differences is critical, because these differences are directly linked to the care and treatment of the patients. Recent studies have attempted to carry out subclassifications of type 2 diabetes based on clinical and genetic differences. However, there is no pathological evidence to support these subclassifications. The pathophysiology of type 2 diabetes is generally divided into insulin resistance in peripheral tissues and pancreatic islet dysfunction. Among them, islet dysfunction causes a deficit in insulin secretion from β-cells. In particular, a deficit in insulin secretion is ascribed to a combination of disruption of the insulin secretory machinery and a decrease in β-cell volume in type 2 diabetes. Recent research has suggested that transdifferentiation and dedifferentiation are involved in the decrease in β-cell volume, and that it might change dynamically depending on the glucose metabolic state. However, it is possible that the numbers of islet cells are decreased in type 2 diabetes. In particular, the loss of endocrine cells due to islet amyloid deposits is an important pathological change in type 2 diabetes in humans. These results show that pathological changes of the islets can be different in each individuals with type 2 diabetes and reflect each pathophysiology, which is useful in establishing further subclassifications and developing tailor-made therapies for type 2 diabetes.

Age-related amyloidosis outside the brain: A state-of-the-art review

Inside and outside the brain, accumulation of amyloid fibrils plays key roles in the pathogenesis of fatal age-related diseases such as Alzheimer's and Parkinson's diseases and wild-type transthyretin amyloidosis. Although the incidence of all amyloidoses increases with age, for some types of amyloidosis aging is known as the main direct risk factor, and these types are typically diseases of elderly people. More than 10 different precursor proteins are known to cause age-associated amyloidosis; these proteins include amyloid β protein, α-synuclein, transthyretin, islet amyloid polypeptide, atrial natriuretic factor, and the newly discovered epidermal growth factor-containing fibulin-like extracellular matrix protein 1. Except for intracerebral amyloidoses, most age-related amyloidoses have been little studied. Indeed, in view of the increasing life expectancy in our societies, understanding how aging is involved in the process of amyloid fibril accumulation and the effects of amyloid deposits on the aging body is extremely important. In this review, we summarize current knowledge about the nature of amyloid precursor proteins, the prevalence, clinical manifestations, and pathogenesis of amyloidosis, and recent advances in our understanding of age-related amyloidoses outside the brain.

β cell aging and age-related diabetes

Type 2 diabetes is characterized by insulin resistance and loss of β cell mass and function. Aging is considered as a major risk factor for development of type 2 diabetes. However, the roles of pancreatic β cell senescence and systemic aging in the pathogenesis of type 2 diabetes in elderly people remain poorly understood. In this review, we aimed to discuss the current findings and viewpoints focusing on β cell aging and the development of type 2 diabetes.

β-cell autophagy: Mechanism and role in β-cell dysfunction

Background

Elucidation of the basic molecular mechanism of autophagy was a breakthrough in understanding various physiological events and pathogenesis of diverse diseases. In the fields of diabetes and metabolism, many cellular events associated with the development of disease or its treatment cannot be explained well without taking autophagy into account. While a grand picture of autophagy has been established, detailed aspects of autophagy, particularly that of selective autophagy responsible for homeostasis of specific organelles or metabolic intermediates, are still ambiguous and currently under intensive research.

Scope of review

Here, results from previous and current studies on the role of autophagy and its dysregulation in the physiology of metabolism and pathogenesis of diabetes are summarized, with an emphasis on the pancreatic β-cell autophagy. In addition to nonselective (bulk) autophagy, machinery and significance of selective autophagy such as mitophagy of pancreatic β-cells is discussed. Novel findings regarding autophagy types other than macroautophagy are also covered, since several types of autophagy or lysosomal degradation pathways other than macroautophagy coexist in pancreatic β-cells.

Major conclusion

Autophagy plays a critical role in cellular metabolism, homeostasis of the intracellular environment and function of organelles such as mitochondria and endoplasmic reticulum. Impaired autophagic activity due to aging, obesity or genetic predisposition could be a factor in the development of β-cell dysfunction and diabetes associated with lipid overload or human-type diabetes characterized by islet amyloid deposition. Modulation of autophagy of pancreatic β-cells is likely to be possible in the near future, which would be valuable in the treatment of diabetes associated with lipid overload or accumulation of islet amyloid.

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Autophagy is critical for cellular metabolism, homeostasis and organelle function.

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Impaired autophagic activity could predispose to β-cell dysfunction and diabetes.

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Several types of autophagy coexist in pancreatic β-cells.

Protein aggregates and proteostasis in aging: Amylin and β-cell function

The ubiquitin-proteasomal-system (UPS) and the autophagy-lysosomal-system (ALS) are both highly susceptible for disturbances leading to the accumulation of cellular damage. A decline of protein degradation during aging results in the formation of oxidatively damaged and aggregated proteins finally resulting in failure of cellular functionality. Besides protein aggregation in response to oxidative damage, amyloids are a different type of protein aggregates able to distract proteostasis and interfere with cellular functionality. Amyloids are clearly linked to the pathogenesis of age-related degenerative diseases such as Alzheimer's disease. Human amylin is one of the peptides forming fibrils in β-sheet conformation finally leading to amyloid formation. In contrast to rodent amylin, human amylin is prone to form amyloidogenic aggregates, proposed to play a role in the pathogenesis of Type 2 Diabetes by impairing β-cell functionality. Since aggregates such as lipofuscin and β-amyloid are known to impair proteostasis, it is likely to assume similar effects for human amylin. In this review, we focus on the effects of IAPP on UPS and ALS and their role in amylin degradation, since both systems play a crucial role in maintaining proteome balance thereby influencing, at least in part, cellular fate and aging.

Involvement of Macrophages in the Pathogenesis of Familial Amyloid Polyneuropathy and Efficacy of Human iPS Cell-Derived Macrophages in Its Treatment

We hypothesized that tissue-resident macrophages in familial amyloid polyneuropathy (FAP) patients will exhibit qualitative or quantitative abnormalities, that may accelerate transthyretin (TTR)-derived amyloid deposition. To evaluate this, we examined the number and subset of tissue-resident macrophages in heart tissue from amyloid-deposited FAP and control patients. In both FAP and control patients, tissue-resident macrophages in heart tissue were all Iba⁺/CD163⁺/CD206⁺ macrophages. However, the number of macrophages was significantly decreased in FAP patients compared with control patients. Furthermore, the proportion of intracellular TTR in CD14⁺ monocytes was reduced in peripheral blood compared with healthy donors. Based on these results, we next examined degradation and endocytosis of TTR in human induced pluripotent stem (iPS) cell-derived myeloid lineage cells (MLs), which function like macrophages. iPS-MLs express CD163 and CD206, and belong to the inhibitory macrophage category. In addition, iPS-MLs degrade both native and aggregated TTR in a cell-dependent manner in vitro. Further, iPS-MLs endocytose aggregated, and especially polymerized, TTR. These results suggest that decreased tissue-localized macrophages disrupt clearance of TTR-derived amyloid deposits, leading to progression of a pathological condition in FAP patients. To improve this situation, clinical application of pluripotent stem cell-derived MLs may be useful as an approach for FAP therapy.

Recipient aging accelerates acquired transthyretin amyloidosis after domino liver transplantation

Domino liver transplantation (DLT) with liver grafts from patients with hereditary transthyretin (TTR) amyloidosis has been performed throughout the world because of a severe liver graft shortage. Reports of acquired systemic TTR amyloidosis in domino liver recipients have been increasing; however, the precise pathogenesis and clinical course of acquired TTR amyloidosis remains unclear. We analyzed the relationship between the occurrence of acquired amyloidosis and clinical features in 22 consecutive domino liver donors with hereditary TTR amyloidosis (10 males and 12 females; mean age at DLT: 37.2 years; TTR mutations: V30M [n = 19], Y114C [n = 1], L55P [n = 1], and S50I [n = 1]) and 22 liver recipients (16 males and 6 females; mean age at DLT, 46.2 years). The mean times from DLT to amyloid first appearance and transplant recipient symptom onset were 8.2 years and 9.9 years, respectively. Kaplan-Meier analysis and quantification of the amyloid deposition revealed aging of recipients correlated with early de novo amyloid deposition. The sex of donors and recipients and the age, disease duration, and disease severity of donors had no significant effect on the latency of de novo amyloid deposition. In conclusion, our results demonstrate that recipient aging is associated with the early onset de novo amyloidosis. Because acquired amyloidosis will likely increase, careful follow-up for early amyloidosis detection and new treatments, including TTR stabilizers and gene-silencing therapies, are required. Liver Transplantation 22 656-664 2016 AASLD.