Integrin ß8 prevents pericyte-myofibroblast transition and renal fibrosis through inhibiting the TGF-ß1/TGFBR1/Smad3 pathway in diabetic kidney disease.

Diabetic kidney disease (DKD) is one of the leading causes to develop end-stage kidney disease worldwide. Pericytes are implicated in the development of tissue fibrosis. However, the underlying mechanisms of pericytes in DKD remain largely unknown. We isolated and cultured primary pericytes and rat mesangial cells (HBZY-1). Western blot and qRT-PCR analysis were used to explore the role and regulatory mechanism of Integrin ß8/transforming growth factor beta 1 (TGF-ß1) pathway. We also constructed pericyte-specific Integrin ß8 knock-in mice as the research objects to determine the role of Integrin ß8 in vivo. We discovered that reduced Integrin ß8 expression was closely associated with pericyte transition in DKD. Overexpressed Integrin ß8 in pericytes dramatically suppressed TGF-ß1/TGF beta receptor 1 (TGFBR1)/Smad3 signaling pathway and protected glomerular endothelial cells (GECs) in vitro. In vivo, pericyte-specific Integrin ß8 knock-in ameliorated pericyte transition, endothelium injury and renal fibrosis in STZ-induced diabetic mice. Mechanistically, Murine double minute 2 (MDM2) was found to increase the degradation of Integrin ß8 and caused TGF-ß1 release and activation. Knockdown MDM2 could partly reverse the decline of Integrin ß8 and suppress pericytes transition. In conclusion, the present findings suggested that upregulated MDM2 expression contributes to the degradation of Integrin ß8 and activation of TGF-ß1/TGFBR1/Smad3 signaling pathway, which ultimately leads to pericyte transition during DKD progression. These results indicate MDM2/Integrin ß8 might be considered as therapeutic targets for DKD.

Analysis of the morphology of retinal vascular cells in zebrafish (Danio rerio).

Background: Zebrafish (Danio rerio) have been established in recent years as a model organism to study Diabetic Retinopathy (DR). Loss of endothelial cells and pericytes is an early hallmark sign of developing DR in the mammalian retina. However, morphology, numbers, ratios, and distributions of different vascular cells in the retinal compartment in zebrafish have not yet been analyzed and compared with the mammalian retina. Methods: The retinal trypsin digest protocol was established on the zebrafish retina. Cell types were identified using the Tg(nflk:EGFP)-reporter line. Cells were quantified using quantitative morphometry. Results: Vascular cells in the zebrafish retina have distinct morphologies and locations. Nuclei of vascular mural cells appear as long and flat nuclei located near the vessel wall. Round nuclei within the vessel walls can be identified as endothelial cells. The vessel diameter decreases from central to peripheral parts of the retina. Additionally, the numbers of vascular cells decrease from central to peripheral parts of the retina. Discussion: The retinal trypsin digest protocol, which can be applied to the zebrafish retina, provides novel insights into the zebrafish retinal vascular architecture. Quantification of the different cell types shows that, in comparison to the mammalian retina, zebrafish have higher numbers of mural cells and an increased mural cell to endothelial cell ratio. This protocol enables to quantify mural cell and endothelial cell numbers, is easily adaptable to different transgenic and mutant zebrafish lines and will enable investigators to compare novel models on a single cell level.

The effect of GLP-1 receptor agonist lixisenatide on experimental diabetic retinopathy.

AIMS: Glucagon-like peptide-1 receptor agonists are effective treatments for type 2 diabetes, effectively lowering glucose without weight gain and with low risk for hypoglycemia. However, their influence on the retinal neurovascular unit remains unclear. In this study, we analyzed the effects of the GLP-1 RA lixisenatide on diabetic retinopathy. METHODS: Vasculo- and neuroprotective effects were assessed in experimental diabetic retinopathy and high glucose-cultivated C. elegans, respectively. In STZ-diabetic Wistar rats, acellular capillaries and pericytes (quantitative retinal morphometry), neuroretinal function (mfERG), macroglia (GFAP western blot) and microglia (immunohistochemistry) quantification, methylglyoxal (LC-MS/MS) and retinal gene expressions (RNA-sequencing) were determined. The antioxidant properties of lixisenatide were tested in C. elegans. RESULTS: Lixisenatide had no effect on glucose metabolism. Lixisenatide preserved the retinal vasculature and neuroretinal function. The macro- and microglial activation was mitigated. Lixisenatide normalized some gene expression changes in diabetic animals to control levels. Ets2 was identified as a regulator of inflammatory genes. In C. elegans, lixisenatide showed the antioxidative property. CONCLUSIONS: Our data suggest that lixisenatide has a protective effect on the diabetic retina, most likely due to a combination of neuroprotective, anti-inflammatory and antioxidative effects of lixisenatide on the neurovascular unit.

Contribution of the hexosamine biosynthetic pathway in the hyperglycemia-dependent and -independent breakdown of the retinal neurovascular unit.

BACKGROUND: Diabetic retinopathy (DR) remains one of the most common complications of diabetes despite great efforts to uncover its underlying mechanisms. The pathogenesis of DR is characterized by the deterioration of the neurovascular unit (NVU), showing damage of vascular cells, activation of glial cells and dysfunction of neurons. Activation of the hexosamine biosynthesis pathway (HBP) and increased protein O-GlcNAcylation have been evident in the initiation of DR in patients and animal models. SCOPE OF REVIEW: The impairment of the NVU, in particular, damage of vascular pericytes and endothelial cells arises in hyperglycemia-independent conditions as well. Surprisingly, despite the lack of hyperglycemia, the breakdown of the NVU is similar to the pathology in DR, showing activated HBP, altered O-GlcNAc and subsequent cellular and molecular dysregulation. MAJOR CONCLUSIONS: This review summarizes recent research evidence highlighting the significance of the HBP in the breakdown of the NVU in hyperglycemia-dependent and -independent manners, and thus identifies joint avenues leading to vascular damage as seen in DR and thus identifying novel potential targets in such retinal diseases.

The Impact of Childhood Traumatization on Diabetes Mellitus Type 2 Risk in World War II Refugees and Their Offspring.

OBJECTIVE: Type 2 diabetes mellitus (T2D) is a chronic disease that is influenced by different factors. The extent to which degree adverse childhood events (ACEs) can modify the potential to development of T2D is still not explored and therefore represents one of the central questions of the childhood escape-late life outcome (DRKS00012419) study. In addition, transgenerational effects were considered in the analyses. METHODS: The study analyzed the association of self-reported traumatic experiences and T2D disease of refugees from East Prussia, who were displaced from their former homeland at the end of the World War II. In addition, an independent sample consisting of participants of first-generation offspring of refugees was analyzed. RESULTS: Of the 242 refugees, all aged between 73 and 93 years, 17.36% reported T2D disease, whereas among the offspring ( n = 272), aged between 47 and 73 years, it was 5.5%, meaning reduced T2D prevalence for both generations compared with the German population of comparable age. In the refugee generation, emotional neglect showed a negative association with development of T2D in later life. In women, separation from close caregivers in childhood showed a negative association with later T2D. In contrast, experiencing emotional abuse in childhood showed a positive association with later T2D. The offspring generation showed no associations of adverse childhood events and reported T2D diagnoses in later life. CONCLUSIONS: Our results demonstrate that individual trauma in childhood is responded to with different mechanisms that can lead to both increased and decreased reported T2D diagnoses in adulthood and thus should by no means be considered in a generalized manner.

Screening Results for Diabetic Retinopathy in Germany in a Real-world Cohort in a Metropolitan Diabetes Care Center.

BACKGROUND: Retinal screening is mandatory to prevent vision loss and blindness due to diabetic retinopathy (DR). The aim of the study was to determine retinopathy screening rates and potential barriers in a German metropolitan diabetes care center. METHODS: Between May and October 2019, 265 patients with diabetes mellitus (95% type 2 diabetes; age 62±13.2 years; diabetes duration 11.1±8.5 years, HbA1c 7.4±1.0%) were referred to an ophthalmologist (referral form with order "Fundoscopy in diabetes mellitus, findings requested," completed documentation form "General practitioner's/diabetologist's report to the ophthalmologist" and prepared documentation form "Ophthalmologist's report"). A structured interview was used to assess the level of compliance with the guidelines and to identify potential barriers to retinopathy screening in a real-world setting, including the quantification of extra payments. RESULTS: All patients were interviewed at 7.9±2.5 months after the referral for retinopathy screening had been issued. According to patient reporting, fundoscopy was performed in 191 (75%) patients. Ophthalmological reports were obtained from 119/191 (62%) patients (46% of the entire cohort). 10/119 (8%) patients had been previously diagnosed with DR and 6/119 (5%) with new-onset DR. In 158/191 (83%) of patients, the referral had been accepted by the ophthalmology practice, of which 25,1% made a co-payment of 36.2±37.6 €. DISCUSSION: Despite a high screening performance in a real-world setting, complete screening in compliance with German guidelines, including written reporting, was found in less than half of the cohort. The prevalence and incidence of DR are high. Even when referred according to the regulations, one-quarter of patients made a co-payment. Efficient solutions to current barriers can emerge with mutual time-saving information prior to examination and feedback about the implementation of findings into treatment.

miRNA-124 Prevents Rat Diabetic Retinopathy by Inhibiting the Microglial Inflammatory Response.

Diabetic retinopathy (DR) is characterized by vasoregression and glial activation. miRNA-124 (miR-124) reduces retinal microglial activation and alleviates vasoregression in a neurodegenerative rat model. Our aim was to determine whether miR-124 affects vascular and neural damage in the early diabetic retina. Diabetes was induced in 8-week-old Wistar rats by streptozotocin (STZ) injection. At 16 and 20 weeks, the diabetic rats were intravitreally injected with miR-124 mimic, and retinae were analyzed at 24 weeks. Microvascular damage was identified by evaluating pericyte loss and acellular capillary (AC) formation. Müller glial activation was assessed by glial fibrillary acidic protein (GFAP) immunofluorescence staining. Microglial activation was determined by immunofluorescent staining of ionized calcium-binding adaptor molecule 1 (Iba1) in whole mount retinae. The neuroretinal function was assessed by electroretinography. The expression of inflammation-associated genes was evaluated by qRT-PCR. A wound healing assay was performed to quantitate the mobility of microglial cells. The results showed that miR-124 treatment alleviated diabetic vasoregression by reducing AC formation and pericyte loss. miR-124 blunted Müller glial- and microglial activation in diabetic retinae and ameliorated neuroretinal function. The retinal expression of inflammatory factors including Tnf-α, Il-1ß, Cd74, Ccl2, Ccl3, Vcam1, Tgf-ß1, Arg1, and Il-10 was reduced by miR-124 administration. The elevated mobility of microglia upon high glucose exposure was normalized by miR-124. The expression of the transcription factor PU.1 and lipid raft protein Flot1 was downregulated by miR-124. In rat DR, miR-124 prevents vasoregression and glial activation, improves neuroretinal function, and modulates microglial activation and inflammatory responses.

Differences in junction-associated gene expression changes in three rat models of diabetic retinopathy with similar neurovascular phenotype.

Diabetic retinopathy, also defined as microvascular complication of diabetes mellitus, affects the entire neurovascular unit with specific aberrations in every compartment. Neurodegeneration, glial activation and vasoregression are observed consistently in models of diabetic retinopathy. However, the order and the severity of these aberrations varies in different models, which is also true in patients. In this study, we analysed rat models of diabetic retinopathy with similar phenotypes to identify key differences in the pathogenesis. For this, we focussed on intercellular junction-associated gene expression, which are important for the communication and homeostasis within the neurovascular unit. Streptozotocin-injected diabetic Wistar rats, methylglyoxal supplemented Wistar rats and polycystin-2 transgenic (PKD) rats were analysed for neuroretinal function, vasoregression and retinal expression of junction-associated proteins. In all three models, neuroretinal impairment and vasoregression were observed, but gene expression profiling of junction-associated proteins demonstrated nearly no overlap between the three models. However, the differently expressed genes were from the main classes of claudins, connexins and integrins in all models. Changes in Rcor1 expression in diabetic rats and Egr1 expression in PKD rats confirmed the differences in upstream transcription factor level between the models. In PKD rats, a possible role for miRNA regulation was observed, indicated by an upregulation of miR-26b-5p, miR-122-5p and miR-300-3p, which was not observed in the other models. In silico allocation of connexins revealed not only differences in regulated subtypes, but also in affected retinal cell types, as well as connexin specific upstream regulators Sox7 and miR-92a-3p. In this study, we demonstrate that, despite their similar phenotype, models for diabetic retinopathy exhibit significant differences in their pathogenic pathways and primarily affected cell types. These results underline the importance for more sensitive diagnostic tools to identify pathogenic clusters in patients as the next step towards a desperately needed personalized therapy.

Glucosamine inhibits extracellular matrix accumulation in experimental diabetic nephropathy.

Introduction: Glucosamine, the intermediate metabolite of the hexosamine biosynthesis pathway (HBP), is widely used as a supplementary drug in patients with osteoarthritis. However, its consequences in such patients concomitantly suffering from diabetic nephropathy is unknown. Methods: The aim of the study was to investigate the effect of exogenous administration of glucosamine in the diabetic kidney. A mouse model of streptozotocin-induced diabetic nephropathy in vivo and cultured endothelial cells in vitro were used in the study. The mice were treated with glucosamine for 6 months. Renal function was evaluated by metabolic cage, and histology of the kidney was estimated by periodic acid-schiff (PAS) staining. The expression of related genes was assessed by real-time PCR, immunofluorescence staining, immunoblotting and ELISA. Results: There was no significant difference in urinary albumin secretion, relative kidney weight, or creatinine clearance between the groups treated with glucosamine and controls. Assessment of the kidney demonstrated reduction in mesangial expansion and fibronectin expression in the diabetic glomeruli treated with glucosamine. Glucosamine treatment significantly decreased α-smooth muscle actin (α-SMA) protein expression in both diabetic and control kidneys, whereas the expression of other fibrosis-related genes and inflammatory factors was unaltered. Moreover, α-SMA colocalized with the endothelial marker CD31 in the diabetic and control kidneys, and glucosamine reduced α-SMA+ ECs in the diabetic glomeruli. In addition, glucosamine suppressed α-SMA expression in endothelial cells treated with or without high glucose. Discussion: In summary, this is the first report to show that glucosamine reduces mesangial expansion and inhibits endothelial-mesenchymal transition in diabetic nephropathy. The underlying mechanisms need to be further investigated.

Cellular phenotypic transitions in diabetic nephropathy: An update.

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in diabetes and is the most common cause of end stage renal disease (ESRD). Renal fibrosis is the final pathological change in DN. It is widely believed that cellular phenotypic switching is the cause of renal fibrosis in diabetic nephropathy. Several types of kidney cells undergo activation and differentiation and become reprogrammed to express markers of mesenchymal cells or podocyte-like cells. However, the development of targeted therapy for DN has not yet been identified. Here, we discussed the pathophysiologic changes of DN and delineated the possible origins that contribute to myofibroblasts and podocytes through phenotypic transitions. We also highlight the molecular signaling pathways involved in the phenotypic transition, which would provide valuable information for the activation of phenotypic switching and designing effective therapies for DN.

Regulation of Podocyte Injury by CircHIPK3/FUS Complex in Diabetic Kidney Disease.

Diabetic kidney disease (DKD) is a major microvascular complication of diabetes mellitus and is one of the leading causes of end-stage kidney disease. Circular RNAs (circRNAs) are a class of endogenous non-coding RNAs that play important roles in various diseases, yet their roles in DKD are poorly understood. CircRNA HIPK3 (circHIPK3), a highly conserved circRNA, is closely related to various cellular functions, including cell proliferation and apoptosis. The association between circHIPK3 and diabetic complications has been well demonstrated in multiple previous studies. However, the role of circHIPK3 in podocyte injury in DKD remains unclear. Herein, we discovered that circHIPK3 expression is markedly elevated in cultured podocytes under high-glucose (HG) conditions and glomeruli of diabetic mice, which is closely associated with podocyte injury in DKD. Functionally, lentivirus-mediated knockdown of circHIPK3 dramatically suppresses HG-induced podocyte apoptosis in vitro. Therapeutically, silencing circHIPK3 by adeno-associated virus-mediated RNA interference ameliorates podocyte injury and albuminuria in STZ-induced diabetic mice. Mechanistically, circHIPK3 facilitates the enrichment of fused in sarcoma (FUS) on the ectodysplasin A2 receptor (EDA2R) promoter, resulting in the upregulation of EDA2R expression and activation of apoptotic signaling. Taken together, these results indicate circHIPK3/FUS/EDA2R axis as a therapeutic target for podocyte injury and DKD progression.

Flavonoids in Treatment of Chronic Kidney Disease.

Chronic kidney disease (CKD) is a progressive systemic disease, which changes the function and structure of the kidneys irreversibly over months or years. The final common pathological manifestation of chronic kidney disease is renal fibrosis and is characterized by glomerulosclerosis, tubular atrophy, and interstitial fibrosis. In recent years, numerous studies have reported the therapeutic benefits of natural products against modern diseases. Substantial attention has been focused on the biological role of polyphenols, in particular flavonoids, presenting broadly in plants and diets, referring to thousands of plant compounds with a common basic structure. Evidence-based pharmacological data have shown that flavonoids play an important role in preventing and managing CKD and renal fibrosis. These compounds can prevent renal dysfunction and improve renal function by blocking or suppressing deleterious pathways such as oxidative stress and inflammation. In this review, we summarize the function and beneficial properties of common flavonoids for the treatment of CKD and the relative risk factors of CKD.

Mitochondrial Oxidative Stress and Cell Death in Podocytopathies.

Podocytopathies are kidney diseases that are driven by podocyte injury with proteinuria and proteinuria-related symptoms as the main clinical presentations. Albeit podocytopathies are the major contributors to end-stage kidney disease, the underlying molecular mechanisms of podocyte injury remain to be elucidated. Mitochondrial oxidative stress is associated with kidney diseases, and increasing evidence suggests that oxidative stress plays a vital role in the pathogenesis of podocytopathies. Accumulating evidence has placed mitochondrial oxidative stress in the focus of cell death research. Excessive generated reactive oxygen species over antioxidant defense under pathological conditions lead to oxidative damage to cellular components and regulate cell death in the podocyte. Conversely, exogenous antioxidants can protect podocyte from cell death. This review provides an overview of the role of mitochondrial oxidative stress in podocytopathies and discusses its role in the cell death of the podocyte, aiming to identify the novel targets to improve the treatment of patients with podocytopathies.

Adverse childhood experiences and late-life diurnal HPA axis activity: Associations of different childhood adversity types and interaction with timing in a sample of older East Prussian World War II refugees.

Adverse childhood experiences (ACEs) have been associated with unfavorable health outcomes throughout the life up to old age. Mechanisms through which ACEs impact later life health are still not entirely clear. There is growing evidence for the idea that alterations in the hypothalamic pituitary adrenal (HPA) axis might cause the effects of ACEs on later health consequences. Only few studies have investigated associations between ACEs and diurnal HPA axis functioning in older adults. Therefore, we investigated the impact of type and timing of ACEs linked to flight of war on diurnal HPA axis activity in a sample of East Prussian World War II refugees aged 74-91 years. We calculated a dichotomous variable according to the (minimum) age at trauma: early ACE (eACE; 0-5 years) and late ACE (lACE; 6-17 years). Multiple linear regression analysis using different ACEs linked to flight of war (war-related trauma, individual experience of violence, neglect) as well as age at trauma and the interactions of ACEs and age at trauma as predictors and three cortisol outcomes (AUCG (area under the curve with respect to the ground), decline (morning to night) and CAR (cortisol awakening response)) was performed. For AUCG, we found a negative association of individual experience of violence only in lACE participants. For decline, a positive association with neglect was observed for the whole study sample. The overall model for CAR was not statistically significant. Our findings support the hypothesis that type as well as timing of ACEs might influence diurnal HPA axis functioning into old age. These findings may contribute to a better understanding of the lifelong influence of ACEs.

Asparaginyl endopeptidase protects against podocyte injury in diabetic nephropathy through cleaving cofilin-1.

Podocyte injury and loss are critical events in diabetic nephropathy (DN); however, the underlying molecular mechanisms remain unclear. Here, we demonstrate that asparaginyl endopeptidase (AEP) protects against podocyte injury through modulating the dynamics of the cytoskeleton. AEP was highly upregulated in diabetic glomeruli and hyperglycemic stimuli treated-podocytes; however, AEP gene knockout and its compound inhibitor treatment accelerated DN in streptozotocin-induced diabetic mice, whereas specific induction of AEP in glomerular cells attenuated podocyte injury and renal function deterioration. In vitro, elevated AEP was involved in actin cytoskeleton maintenance and anti-apoptosis effects. Mechanistically, we found that AEP directly cleaved the actin-binding protein cofilin-1 after the asparagine 138 (N138) site. The protein levels of endogenous cofilin-1 1-138 fragments were upregulated in diabetic podocytes, consistent with the changes in AEP levels. Importantly, we found that cofilin-1 1-138 fragments were remarkably unphosphorylated than full-length cofilin-1, indicating the enhanced cytoskeleton maintenance activity of cofilin-1 1-138. Then we validated cofilin-1 1-138 could rescue podocytes from cytoskeleton disarrangement and injury in diabetic conditions. Taken together, our data suggest a protective role of elevated AEP in podocyte injury during DN progression through cleaving cofilin-1 to maintain podocyte cytoskeleton dynamics and defend damage.

Accumulation of acetaldehyde in aldh2.1-/- zebrafish causes increased retinal angiogenesis and impaired glucose metabolism.

Reactive carbonyl species (RCS) are spontaneously formed in the metabolism and modify and impair the function of DNA, proteins and lipids leading to several organ complications. In zebrafish, knockout of the RCS detoxifying enzymes glyoxalase 1 (Glo 1), aldehyde dehydrogenase 3a1 (Aldh3a1) and aldo-ketoreductase 1a1a (Akr1a1a) showed a signature of elevated RCS which specifically regulated glucose metabolism, hyperglycemia and diabetic organ damage. aldh2.1 was compensatory upregulated in glo1-/- animals and therefore this study aimed to investigate the detoxification ability for RCS by Aldh2.1 in zebrafish independent of ethanol exposure. aldh2.1 knockout zebrafish were generated using CRISPR/Cas9 and subsequently analyzed on a histological, metabolomic and transcriptomic level. aldh2.1-/- zebrafish displayed increased endogenous acetaldehyde (AA) inducing an increased angiogenesis in retinal vasculature. Expression and pharmacological interventional studies identified an imbalance of c-Jun N-terminal kinase (JNK) and p38 MAPK induced by AA, which mediate an activation of angiogenesis. Moreover, increased AA in aldh2.1-/- zebrafish did not induce hyperglycemia, instead AA inhibited the expression of glucokinase (gck) and glucose-6-phosphatase (g6pc), which led to an impaired glucose metabolism. In conclusion, the data have identified AA as the preferred substrate for Aldh2.1's detoxification ability, which subsequently causes microvascular organ damage and impaired glucose metabolism.

Protective Effects of Transient Glucose Exposure in Adult C. elegans.

C. elegans are used to study molecular pathways, linking high glucose levels (HG) to diabetic complications. Persistent exposure of C. elegans to a HG environment induces the mitochondrial formation of reactive oxygen species (ROS) and advanced glycation endproducts (AGEs), leading to neuronal damage and decreased lifespan. Studies suggest that transient high glucose exposure (TGE) exerts different effects than persistent exposure. Thus, the effects of TGE on ROS, AGE-formation and life span were studied in C. elegans. Four-day TGE (400 mM) as compared to controls (0mM) showed a persistent increase of ROS (4-days 286 ± 40 RLUs vs. control 187 ± 23 RLUs) without increased formation of AGEs. TGE increased body motility (1-day 0.14 ± 0.02; 4-days 0.15 ± 0.01; 6-days 0.16 ± 0.02 vs. control 0.10 ± 0.02 in mm/s), and bending angle (1-day 17.7 ± 1.55; 3-days 18.7 ± 1.39; 6-days 20.3 ± 0.61 vs. control 15.3 ± 1.63 in degree/s) as signs of neuronal damage. Lifespan was increased by 27% (21 ± 2.4 days) after one-day TGE, 34% (22 ± 1.2 days) after four-days TGE, and 26% (21 ± 1.4 days) after six-days TGE vs. control (16 ± 1.3 days). These experiments suggest that TGE in C. elegans has positive effects on life span and neuronal function, associated with mildly increased ROS-formation. From the perspective of metabolic memory, hormetic effects outweighed the detrimental effects of a HG environment.

pdx1 Knockout Leads to a Diabetic Nephropathy- Like Phenotype in Zebrafish and Identifies Phosphatidylethanolamine as Metabolite Promoting Early Diabetic Kidney Damage.

The pdx1-/- zebrafish mutant was recently established as a novel animal model of diabetic retinopathy. In this study, we investigate whether knockout of pdx1 also leads to diabetic kidney disease (DKD). pdx1-/- larvae exhibit several signs of early DKD, such as glomerular hypertrophy, impairments in the filtration barrier corresponding to microalbuminuria, and glomerular basement membrane (GBM) thickening. Adult pdx1-/- mutants show progressive GBM thickening in comparison with the larval state. Heterozygous pdx1 knockout also leads to glomerular hypertrophy as initial establishment of DKD similar to the pdx1-/- larvae. RNA sequencing of adult pdx1+/- kidneys uncovered regulations in multiple expected diabetic pathways related to podocyte disruption and hinting at early vascular dysregulation without obvious morphological alterations. Metabolome analysis and pharmacological intervention experiments revealed the contribution of phosphatidylethanolamine in the early establishment of kidney damage. In conclusion, this study identified the pdx1 mutant as a novel model for the study of DKD, showing signs of the early disease progression already in the larval stage and several selective features of later DKD in adult mutants.

The activity of glyoxylase 1 is regulated by glucose-responsive phosphorylation on Tyr136.

OBJECTIVE: Methylglyoxal (MG) is a highly reactive α-oxoaldehyde that glycates proteins. MG has been linked to the development of diabetic complications: MG is the major precursor of advanced glycation end products (AGEs), a risk marker for diabetic complications in humans. Furthermore, flies and fish with elevated MG develop insulin resistance, obesity, and hyperglycemia. MG is detoxified in large part through the glyoxalase system, whose rate-limiting enzyme is glyoxalase I (Glo1). Hence, we aimed to study how Glo1 activity is regulated. METHODS: We studied the regulation and effect of post-translational modifications of Glo1 in tissue culture and in mouse models of diabetes. RESULTS: We show that Glo1 activity is promoted by phosphorylation on Tyrosine 136 via multiple kinases. We find that Glo1 Y136 phosphorylation responds in a bimodal fashion to glucose levels, increasing in cell culture from 0 mM to 5 mM (physiological) glucose, and then decreasing at higher glucose concentrations, both in cell culture and in mouse models of hyperglycemia. CONCLUSIONS: These data, together with published findings that elevated MG leads to hyperglycemia, suggest the existence of a deleterious positive feedback loop whereby hyperglycemia leads to reduced Glo1 activity, contributing to elevated MG levels, which in turn promote hyperglycemia. Hence, perturbations elevating either glucose or MG have the potential to start an auto-amplifying feedback loop contributing to diabetic complications.