STK35 Gene Therapy Attenuates Endothelial Dysfunction and Improves Cardiac Function in Diabetes

Diabetic cardiomyopathy (DCM) is characterized by microvascular pathology and interstitial fibrosis that leads to progressive heart failure. The mechanisms underlying DCM pathogenesis remain obscure, and no effective treatments for the disease have been available. In the present study, we observed that STK35, a novel kinase, is decreased in the diabetic human heart. High glucose treatment, mimicking hyperglycemia in diabetes, downregulated STK35 expression in mouse cardiac endothelial cells (MCEC). Knockdown of STK35 attenuated MCEC proliferation, migration, and tube formation, whereas STK35 overexpression restored the high glucose-suppressed MCEC migration and tube formation. Angiogenesis gene PCR array analysis revealed that HG downregulated the expression of several angiogenic genes, and this suppression was fully restored by STK35 overexpression. Intravenous injection of AAV9-STK35 viral particles successfully overexpressed STK35 in diabetic mouse hearts, leading to increased vascular density, suppression of fibrosis in the heart, and amelioration of left ventricular function. Altogether, our results suggest that hyperglycemia downregulates endothelial STK35 expression, leading to microvascular dysfunction in diabetic hearts, representing a novel mechanism underlying DCM pathogenesis. Our study also emerges STK35 is a novel gene therapeutic target for preventing and treating DCM.

Loss of PDK1 Induces Meiotic Defects in Oocytes From Diabetic Mice

Maternal diabetes has been shown to impair oocyte quality; however, the underlying mechanisms remain unclear. Here, using a streptozotocin (STZ)-induced diabetic mouse model, we first detected and reduced expression of pyruvate dehydrogenase kinase 1 (PDK1) in diabetic oocytes, accompanying with the lowered phosphorylation of serine residue 232 on α subunit of the pyruvate dehydrogenase (PDH) complex (Ser232-PDHE1α). Importantly, forced expression of PDK1 not only elevated the phosphorylation level of Ser232-PDHE1α, but also partly prevented the spindle disorganization and chromosome misalignment in oocytes from diabetic mice, with no beneficial effects on metabolic dysfunction. Moreover, a phospho-mimetic S232D-PDHE1α mutant is also capable of ameliorating the maternal diabetes-associated meiotic defects. In sum, our data indicate that PDK1-controlled Ser232-PDHE1α phosphorylation pathway mediates the effects of diabetic environment on oocyte competence.

Diabetic mice have retinal and choroidal blood flow deficits and electroretinogram deficits with impaired responses to hypercapnia

Purpose The purpose of this study was to investigate neuronal and vascular functional deficits in the retina and their association in a diabetic mouse model. We measured electroretinography (ERG) responses and choroidal and retinal blood flow (ChBF, RBF) with magnetic resonance imaging (MRI) in healthy and diabetic mice under basal conditions and under hypercapnic challenge. Methods Ins2Akita diabetic (Diab, n = 8) and age-matched, wild-type C57BL/6J mice (Ctrl, n = 8) were studied under room air and moderate hypercapnia (5% CO2). Dark-adapted ERG a-wave, b-wave, and oscillatory potentials (OPs) were measured for a series of flashes. Regional ChBF and RBF under air and hypercapnia were measured using MRI in the same mice. Results Under room air, Diab mice had compromised ERG b-wave and OPs (e.g., b-wave amplitude was 422.2±10.7 μV in Diab vs. 600.1±13.9 μV in Ctrl, p < 0.001). Under hypercapnia, OPs and b-wave amplitudes were significantly reduced in Diab (OPs by 30.3±3.0% in Diab vs. -3.0±3.6% in Ctrl, b-wave by 17.9±1.4% in Diab vs. 1.3±0.5% in Ctrl). Both ChBF and RBF had significant differences in regional blood flow, with Diab mice having substantially lower blood flow in the nasal region (ChBF was 5.4±1.0 ml/g/min in Diab vs. 8.6±1.0 ml/g/min in Ctrl, RBF was 0.91±0.10 ml/g/min in Diab vs. 1.52±0.24 ml/g/min in Ctrl). Under hypercapnia, ChBF increased in both Ctrl and Diab without significant group difference (31±7% in Diab vs. 17±7% in Ctrl, p > 0.05), but an increase in RBF was not detected for either group. Conclusions Inner retinal neuronal function and both retinal and choroidal blood flow were impaired in Diab mice. Hypercapnia further compromised inner retinal neuronal function in diabetes, while the blood flow response was not affected, suggesting that the diabetic retina has difficulty adapting to metabolic challenges due to factors other than impaired blood flow regulation.

Peripheral Neuropathy Presents Similar Symptoms and Pathological Changes in Both High-Fat Diet and Pharmacologically Induced Pre- and Diabetic Mouse Models

The objective of the study was to compare the effects of experimentally induced type 1 or type 2 diabetes (T1D or T2D) on the functional, structural and biochemical properties of mouse peripheral nerves. Eight-week-old C57BL/6 mice were randomly assigned into three groups, including the control (CTRL, chow-fed), STZ (streptozotocin (STZ)-injected), and HFD (high-fat diet (HFD)-fed) group. After 18-weeks of experimental treatment, HFD mice had higher body weights and elevated levels of plasma lipids, while STZ mice developed hyperglycemia. STZ-treated mice, after an extended period of untreated diabetes, developed motor and sensory nerve conduction-velocity deficits. Moreover, relative to control fibers, pre- and diabetic axons were lower in number and irregular in shape. Animals from both treatment groups manifested a pronounced overexpression of nNOS and a reduced expression of SOD1 proteins in the sciatic nerve, indicating oxidative–nitrosative stress and ineffective antioxidant protection in the peripheral nervous system of these mice. Collectively, STZ- and HFD-treated mice revealed similar characteristics of peripheral nerve damage, including a number of morphological and electrophysiological pathologies in the sciatic nerve. While hyperglycemia is a large component of diabetic neuropathy pathogenesis, the non-hyperglycemic effects of diabetes, including dyslipidemia, may also be of importance in the development of this condition.

Adiponectin Accumulation in the Tetinal Vascular Endothelium and its Possible Role in Preventing Early Diabetic Microvascular Damage

Adiponectin (APN), a protein abundantly secreted from adipocytes, has been reported to possess beneficial effects on cardiovascular diseases in association with its accumulation on target organs and cells by binding to T-cadherin. However, little is known about the role of APN in the development of diabetic microvascular complications, such as diabetic retinopathy (DR). Here we investigated the impact of APN on the progression of early retinal vascular damage using a streptozotocin (STZ)-induced diabetic mouse model. Our immunofluorescence results clearly showed T-cadherin-dependent localization of APN in the vascular endothelium of retinal arterioles, which was progressively decreased during the course of diabetes. Such reduction of retinal APN accompanied the early features of DR, represented by increased vascular permeability, and was prevented by glucose-lowering therapy with dapagliflozin, a selective sodium-glucose co-transporter 2 inhibitor. In addition, APN deficiency resulted in severe vascular permeability under relatively short-term hyperglycemia, together with a significant increase in vascular cellular adhesion molecule-1 (VCAM-1) and a reduction in claudin-5 in the retinal endothelium. The present study demonstrated a possible protective role of APN against the development of DR.

Consequences of Both Coxsackievirus B4 and Type 1 Diabetes on Female Non-Obese Diabetic Mouse Kidneys

Despite the 2019 Executive Order on Advancing American Kidney Health Initiative, kidney disease has moved up in rank from the 9th to the 8th leading cause of death in the United States. A recent push in the field of nephrology has been to identify molecular markers and/or molecular profiles involved in kidney disease process or injury that can help identify the cause of injury and predict patient outcomes. While these studies have had moderate success, they have not yet considered that many of the health conditions that cause kidney disease (diabetes, hypertension, etc.) can also be caused by environmental factors (such as viruses), which in and of themselves can cause kidney disease. Thus, the goal of this study was to identify molecular and phenotypic profiles that can differentiate kidney injury caused by diabetes (a health condition resulting in kidney disease) and coxsackievirus B4 (CVB4) exposure (which can cause diabetes and/or kidney disease), both alone and together. Non-obese diabetic (NOD) mice were used for this study due to their susceptibility to both type 1 diabetes (T1D)- and CVB4-mediated kidney injury, in order to glean a better understanding of how hyperglycemia and viral exposure, when occurring on their own and in combination, may alter the kidneys’ molecular and phenotypic profiles. While no changes in kidney function were observed, molecular biomarkers of kidney injury were significantly up- and downregulated based on T1D and CVB4 exposure, both alone and together, but not in a predictable pattern. By combining individual biomarkers with function and phenotypic measurements (i.e., urinary albumin creatinine ratio, serum creatinine, kidney weight, and body weight), we were able to perform an unbiased separation of injury group based on the type of injury. This study provides evidence that unique kidney injury profiles within a kidney disease health condition are identifiable, and will help us to identify the causes of kidney injury in the future.

Sirtuin 3 overexpression preserves maximal sarco(endo)plasmic reticulum calcium ATPase activity in the skeletal muscle of mice subjected to high fat-high sucrose-feeding

Sarco(endo)plasmic reticulum calcium (Ca²⁺) ATPase (SERCA) transports Ca²⁺ in muscle. Impaired SERCA activity contributes to diabetic myopathy. Sirtuin (SIRT) 3 regulates muscle metabolism and function. However, it is unknown if SIRT3 regulates muscle SERCA activity. We determined if SIRT3 overexpression enhances SERCA activity in mouse gastrocnemius muscle and if SIRT3 overexpression preserves gastrocnemius SERCA activity in a model of type 2 diabetes, induced by high fat-high sucrose (HFHS)-feeding. We also determined if the acetylation status of SERCA proteins in mouse gastrocnemius is altered by SIRT3 overexpression or HFHS-feeding. Wild-type (WT) mice and SIRT3 transgenic (SIRT3_TG) mice, overexpressing SIRT3 in skeletal muscle, were fed a standard- or HFHS-diet for 4-months. SIRT3_TG and WT mice developed obesity and glucose intolerance after 4-months of HFHS-feeding. SERCA <i>V</i>_max was higher in gastrocnemius of SIRT3TG mice, compared to WT mice. HFHS-fed mice had lower SERCA1a protein levels and lower SERCA <i>V</i>_max in their gastrocnemius than control-fed mice. The decrease in SERCA <i>V</i>_max in gastrocnemius muscle due to HFHS-feeding was attenuated by SIRT3 overexpression in HFHS-fed SIRT3_TG mice. SERCA1a and SERCA2a acetylation in mouse gastrocnemius was not altered by genotype or diet. These findings suggest SIRT3 overexpression improves SERCA function in diabetic mouse skeletal muscle.

Polyphenol Metabolite Pyrogallol-O-Sulfate Decreases Microglial Activation and VEGF in Retinal Pigment Epithelium Cells and Diabetic Mouse Retina

(Poly)phenol-derived metabolites are small molecules resulting from (poly)phenol metabolization after ingestion that can be found in circulation. In the last decade, studies on the impact of (poly)phenol properties in health and cellular metabolism accumulated evidence that (poly)phenols are beneficial against human diseases. Diabetic retinopathy (DR) is characterized by inflammation and neovascularization and targeting these is of therapeutic interest. We aimed to study the effect of pyrogallol-O-sulfate (Pyr-s) metabolite in the expression of proteins involved in retinal glial activation, neovascularization, and glucose transport. The expression of PEDF, VEGF, and GLUT-1 were analyzed upon pyrogallol-O-sulfate treatment in RPE cells under high glucose and hypoxia. To test its effect on a diabetic mouse model, Ins2Akita mice were subjected to a single intraocular injection of the metabolite and the expression of PEDF, VEGF, GLUT-1, Iba1, or GFAP measured in the neural retina and/or retinal pigment epithelium (RPE), two weeks after treatment. We observed a significant decrease in the expression of pro-angiogenic VEGF in RPE cells. Moreover, pyrogallol-O-sulfate significantly decreased the expression of microglial marker Iba1 in the diabetic retina at different stages of disease progression. These results highlight the potential pyrogallol-O-sulfate metabolite as a preventive approach towards DR progression, targeting molecules involved in both inflammation and neovascularization.