Florin Despa

In humans, hypersecretion of amyloidogenic amylin (islet amyloid polypeptide, IAPP) in the setting of insulin resistance and type 2 diabetes (T2D) promotes systemic oligomerization and tissue deposition, with deposits identified in failing human hearts and the cerebrovasculature of patients with Alzheimer's Disease. In the renal vasculature, amylin aggregation disrupts microvascular integrity, activating hypoxia signaling pathways and contributing to maladaptive erythropoietic responses, including excess erythrocytosis. We hypothesized that amyloid‐forming amylin would activate hypoxia‐inducible factor (HIF) signaling, leading to metabolic alterations in liver and heart during T2D pathogenesis. To investigate this, we used the HIP rat, which expresses human amylin specifically in pancreatic β‐cells, comparing tissues from 14 to 16‐month‐old rats with those from age‐matched wild‐type, hyperglycemic UCD and amylin‐knockout (AKO) rats. We found greater accumulation of HIF‐1α and HIF‐2α in HIP rat livers compared with those in other groups, alongside increased expression of HIF‐1 target genes. Mitochondrial ETS capacity was elevated in HIP rat livers, in conjunction with the formation of mitochondrial supercomplexes. Amylin aggregates formed in the hearts of HIP rats, alongside HIF‐1α and HIF‐2α accumulation. This was associated with suppression of ETS capacity, and increased p‐AMPK/AMPK, indicating possible cardiac energetic impairment. Pancreatic secretion of amyloidogenic amylin is thus associated with HIF activation in key metabolic organs beyond the renal vasculature, and occurs alongside mitochondrial alterations in liver and heart that are consistent with sustained hypoxic stress. Our results, alongside previous work, suggest that amylin dysregulation is an overlooked, human‐relevant aspect of diabetes pathogenesis, and as such, a potential therapeutic target.

Aims/hypothesis Women with prior gestational diabetes mellitus (GDM) have higher incidence of age-associated diseases, including type 2 diabetes, CVD and cognitive impairment. Human studies cannot readily determine whether GDM causes these conditions or the underlying mechanisms. Here we used a well-validated rat model of GDM to address these questions. Methods Rats with beta cell-specific expression of human amylin, a pancreatic hormone, were used as a GDM model. Five-month-old female rats were randomly assigned to no-pregnancy, one-pregnancy and two-pregnancies experimental groups. GTTs and transthoracic echocardiography were performed at baseline and during the postpartum period. At 18 months of age, the novel object recognition test was administered, followed by euthanasia and organ collection. Results All female rats developed glucose intolerance and showed cardiac remodelling and impaired left ventricular relaxation with ageing. Glucose intolerance was exacerbated in rats with prior GDM pregnancies compared with nulliparous rats, with significant differences starting at 9 months of age. However, blood glucose levels were comparable in the three groups during the course of the study. Rats with two GDM-complicated pregnancies had increased left ventricular mass compared with the other groups following the second pregnancy and until the end of the study. At 18 months of age, rats with prior GDM pregnancies presented aggravated demyelination, particularly in the hippocampus and mid-brain region, oxidative stress and neuroinflammation, and had a lower recognition index in the novel object recognition test compared with nulliparous rats. Higher parity exacerbated these effects. Shorter telomeres and reduced mitochondrial DNA content, two hallmarks of biological ageing, were found in the brain, heart and pancreas of rats with prior GDM. Conclusions/interpretation These findings support the concept that GDM is a sex-specific risk factor for ageing-related diseases, and point to accelerated cellular ageing as a contributing mechanism. Data availability Cardiac echocardiography and GTT data are available at Dataverse under the identifier https://doi.org/10.7910/DVN/R2HITG Graphical Abstract

Amylin is an amyloidogenic neuroendocrine hormone co-synthesized and co-secreted with insulin from the pancreas. It readily crosses the blood–brain barrier and synergistically forms mixed amyloid plaques with β-amyloid (Aβ) in brain parenchyma. Parenchymal amylin-Aβ plaques are found in both sporadic and early-onset familial Alzheimer’s disease (AD), yet their (patho)physiological role remains elusive, particularly due to a lack of detection modalities for these mixed plaques. Previously, we developed an enzyme-linked immunosorbent assay (ELISA) capable of detecting amylin-Aβ hetero-oligomers in brain lysate and blood using a polyclonal anti-amylin antibody to capture hetero-oligomers and a monoclonal anti-Aβ mid-domain detection antibody combination. This combination allows for the recognition of distinct amylin epitopes, which remain accessible after amylin-Aβ oligomerization has begun, and precise detection of Aβ epitopes available after oligomer formation. The utility of this assay is evidenced in our previous report, wherein differences in hetero-oligomer content in brain tissue from patients with and without AD and patients with and without diabetes were distinguished. Additionally, using AD model rats, we provided evidence that our assay can be employed for the detection of amylin-Aβ in blood. This assay and protocol are important innovations in the field of AD research because they meet an unmet need to detect mixed amyloid plaques that, if targeted therapeutically, could reduce AD progression and severity.

Background: Islet amyloid polypeptide (amylin) secreted from the pancreas crosses the blood brain barrier into the brain parenchyma and interacts with Alzheimer’s disease (AD) associated cerebral β‐amyloid (Aβ) plaques, which are found in both sporadic and early‐onset familial AD. Immunoprecipitated amylin from human AD brain tissue analyzed by Western blot using an anti‐Aβ antibody detects Aβ immunoreactivity, which indicates that the amylin and Aβ peptides aggregate in the brains of humans with AD, forming amylin‐Aβ hetero‐oligomers that are sodium dodecyl sulfate (SDS)‐soluble. We report the development of an ELISA to detect amylin‐Aβ hetero‐oligomers in brain tissue and blood.Method: The amylin‐Aβ ELISA relies on a monoclonal anti‐Aβ middomain antibody (detection) and a polyclonal anti‐amylin antibody (capture) designed to recognize an epitope that is distinct from the high affinity amylin‐Aβ binding sites. We screened temporal cortex homogenates obtained from 13 cognitively unaffected (CU) humans and 47 persons with sporadic AD (sAD) for amylin‐Aβ hetero‐oligomers. Individuals were of similar age (sAD, 85.65 ± 7.04 years vs. CU, 87.22 ± 7.30 years; p = 0.482). Brain tissue amylin and Aβ concentrations were measured using conventional ELISAs. Amylin‐Aβ oligomer levels were also measured in whole blood lysates from APP/PS1 rats and APP/PS1 rats expressing amyloid forming amylin in the pancreas (APP/PS1/HIP rats; all rats age‐matched, 16‐months).Result: The brains of most AD patients had detectable amylin‐Aβ hetero‐oligomer concentrations, whereas about half of those CU had brain tissue amylin‐Aβ hetero‐oligomers below the detection limit (0.02 ng/mg total protein; one‐way ANOVA, P < 0.0001). Amylin‐Aβ hetero‐oligomers were more common in brains with frequent neuritic plaques (CERAD C). Higher brain tissue amylin‐Aβ hetero‐oligomer levels were associated with greater brain tissue amylin concentrations (r = 0.38; P < 0.05). There was no correlation between cerebral amylin‐Aβ hetero‐oligomer accumulation and age in the analysis of samples from sAD and CU groups (r = ‐0.22; P > 0.05). Levels of amylin‐Aβ hetero‐oligomers in whole blood lysates obtained from APP/PS1/HIP rats were higher than those from APP/PS1 littermates (P < 0.05).Conclusion: Studies are needed to determine the extent to which amylin‐Aβ hetero‐oligomerization can be detected in human blood.

Background: Mitochondrial dysfunction contributes to the cardiac remodeling triggered by type 2 diabetes (T2D). Mitochondrial Ca ²⁺ concentration ([Ca ²⁺ ] _m ) modulates the oxidative state and cytosolic Ca ²⁺ regulation. Thus, we investigated how T2D affects mitochondrial Ca ²⁺ fluxes, the downstream consequences on myocyte function, and the effects of normalizing mitochondrial Ca ²⁺ transport. Methods and Results: We compared myocytes/hearts from transgenic rats with late‐onset T2D (rats that develop late‐onset T2D due to heterozygous expression of human amylin in the pancreatic β‐cells [HIP] model) and their nondiabetic wild‐type (WT) littermates. [Ca ²⁺ ] _m was significantly lower in myocytes from diabetic HIP rats compared with WT cells. Ca ²⁺ extrusion through the mitochondrial Na ⁺ /Ca ²⁺ exchanger (mitoNCX) was elevated in HIP versus WT myocytes, particularly at moderate and high [Ca ²⁺ ] _m , while mitochondrial Ca ²⁺ uptake was diminished. Mitochondrial Na ⁺ concentration was comparable in WT and HIP rat myocytes and remained remarkably stable while manipulating mitoNCX activity. Lower [Ca ²⁺ ] _m was associated with oxidative stress, increased sarcoplasmic reticulum Ca ²⁺ leak in the form of Ca ²⁺ sparks, and mitochondrial dysfunction in T2D hearts. MitoNCX inhibition with CGP‐37157 reduced oxidative stress, Ca ²⁺ spark frequency, and stress‐induced arrhythmias in HIP rat hearts while having no significant effect in WT rats. In contrast, activation of the mitochondrial Ca ²⁺ uniporter with SB‐202190 enhanced spontaneous sarcoplasmic reticulum Ca ²⁺ release and had no significant effect on arrhythmias in both WT and HIP rat hearts. Conclusions: [Ca ²⁺ ] _m is reduced in myocytes from rats with T2D due to a combination of exacerbated mitochondrial Ca ²⁺ extrusion through mitoNCX and impaired mitochondrial Ca ²⁺ uptake. Partial mitoNCX inhibition limits sarcoplasmic reticulum Ca ²⁺ leak and arrhythmias in T2D hearts, whereas mitochondrial Ca ²⁺ uniporter activation does not.

Type‐2 diabetes raises the risk for Alzheimer's disease (AD)‐type dementia and the conversion from mild cognitive impairment to dementia, yet mechanisms connecting type‐2 diabetes to AD remain largely unknown. Amylin, a pancreatic β‐cell hormone co‐secreted with insulin, participates in the central regulation of satiation, but also forms pancreatic amyloid in persons with type‐2 diabetes and synergistically interacts with brain amyloid β (Aβ) pathology, in both sporadic and familial Alzheimer's disease (AD). Growing evidence from studies of tumor growth, together with early observations in skeletal muscle, indicates amylin as a potential trigger of cellular metabolic reprogramming. Because the blood, cerebrospinal fluid, and brain parenchyma in humans with AD have increased concentrations of amylin, amylin‐mediated pathological processes in the brain may involve neuronal metabolic remodeling. This review summarizes recent progress in understanding the link between prediabetic hypersecretion of amylin and risk of neuronal metabolic remodeling and AD and suggests nutritional and medical effects of food constituents that might prevent and/or ameliorate amylin‐mediated neuronal metabolic remodeling.