Protective effect of the tunneling nanotube-TNFAIP2/M-sec system on podocyte autophagy in diabetic nephropathy

Podocyte injury leading to albuminuria is a characteristic feature of diabetic nephropathy (DN). Hyperglycemia and advanced glycation end products (AGEs) are major determinants of DN. However, the underlying mechanisms of podocyte injury remain poorly understood. The cytosolic protein TNFAIP2/M-Sec is required for tunneling nanotubes (TNTs) formation, which are membrane channels that transiently connect cells, allowing organelle transfer. Podocytes express TNFAIP2 and form TNTs, but the potential relevance of the TNFAIP2-TNT system in DN is unknown. We studied TNFAIP2 expression in both human and experimental DN and the renal effect of tnfaip2 deletion in streptozotocin-induced DN. Moreover, we explored the role of the TNFAIP2-TNT system in podocytes exposed to diabetes-related insults. TNFAIP2 was overexpressed by podocytes in both human and experimental DN and exposre of podocytes to high glucose and AGEs induced the TNFAIP2-TNT system. In diabetic mice, tnfaip2 deletion exacerbated albuminuria, renal function loss, podocyte injury, and mesangial expansion. Moreover, blockade of the autophagic flux due to lysosomal dysfunction was observed in diabetes-injured podocytes both in vitro and in vivo and exacerbated by tnfaip2 deletion. TNTs allowed autophagosome and lysosome exchange between podocytes, thereby ameliorating AGE-induced lysosomal dysfunction and apoptosis. This protective effect was abolished by tnfaip2 deletion, TNT inhibition, and donor cell lysosome damage. By contrast, Tnfaip2 overexpression enhanced TNT-mediated transfer and prevented AGE-induced autophagy and lysosome dysfunction and apoptosis. In conclusion, TNFAIP2 plays an important protective role in podocytes in the context of DN by allowing TNT-mediated autophagosome and lysosome exchange and may represent a novel druggable target.Abbreviations: AGEs: advanced glycation end products; AKT1: AKT serine/threonine kinase 1; AO: acridine orange; ALs: autolysosomes; APs: autophagosomes; BM: bone marrow; BSA: bovine serum albumin; CTSD: cathepsin D; DIC: differential interference contrast; DN: diabetic nephropathy; FSGS: focal segmental glomerulosclerosis; HG: high glucose; KO: knockout; LAMP1: lysosomal-associated membrane protein 1; LMP: lysosomal membrane permeabilization; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; PI3K: phosphoinositide 3-kinase; STZ: streptozotocin; TNF: tumor necrosis factor; TNFAIP2: tumor necrosis factor, alpha-induced protein 2; TNTs: tunneling nanotubes; WT: wild type.

Reversal of albuminuria by combined AM6545 and perindopril therapy in experimental diabetic nephropathy

BACKGROUND AND PURPOSE

The endocannabinoid (EC) system has been implicated in the pathogenesis of diabetic nephropathy (DN). We investigated the effects of peripheral blockade of the cannabinoid CB₁ receptor as an add-on treatment to ACE-inhibition in type 1 diabetic mice (DM) with established albuminuria.

EXPERIMENTAL APPROACH

Renal functional parameters (albumin excretion rate, creatinine clearance), tubular injury, renal structure, both EC and CB receptor levels and markers of podocyte dysfunction, fibrosis and inflammation were studied in streptozotocin-induced DM treated for 14 weeks with vehicle, the ACE-inhibitor perindopril (2 mg·kg^-1 ·day^-1 ), peripherally-restricted CB₁ receptor antagonist AM6545 (10 mg·kg^-1 ·day^-1 ) or both. Treatments began at 8 weeks after diabetes onset, when early DN is established.

KEY RESULTS

CB₁ receptors were overexpressed in DM and neither perindopril nor AM6545 altered this effect, while both drugs abolished diabetes-induced overexpression of angiotensin AT₁ receptors. Single treatment with either AM6545 or perindopril significantly reduced progression of albuminuria, down-regulation of nephrin and podocin, inflammation and expression of markers of fibrosis. However, reversal of albuminuria was only observed in mice administered both treatments. The ability of the combination therapy to completely abolish slit diaphragm protein loss, monocyte infiltration, overexpression of inflammatory markers and favour macrophage polarization towards an M2 phenotype may explain this greater efficacy. In vitro experiments confirmed that CB₁ receptor activation directly inhibits retinoic acid-induced nephrin expression in podocytes and IL-4-induced M2 polarization in macrophages.

CONCLUSION AND IMPLICATIONS

Peripheral CB₁ receptor blockade used as add-on treatment to ACE-inhibition reverses albuminuria, nephrin loss and inflammation in DM.

Cannabinoid Receptors in Diabetic Kidney Disease

PURPOSE OF REVIEW

The purpose of this review is to examine and summarize studies assessing the relevance of the endocannabinoid system (ECS) in diabetic kidney disease (DKD).

RECENT FINDINGS

Endocannabinoids and endocannabinoid receptors of type 1 (CB1R) and of type 2 (CB2R) are present in the normal kidney. Expression of CB1R and CB2R is altered in experimental DKD. Studies in experimental animals and cultured kidney cells show a beneficial effect of peripheral CB1R blockade and CB2R activation in DKD and an even greater efficacy of a combined treatment. Preclinical studies confirm that both CB1R and CB2R are implicated in the pathogenesis of DKD and may represent novel targets for treatment. However, we need to gain a better understanding of the ECS prior to move to human clinical trial.

MicroRNA and Microvascular Complications of Diabetes

In the last decade, miRNAs have received substantial attention as potential players of diabetes microvascular complications, affecting the kidney, the retina, and the peripheral neurons. Compelling evidence indicates that abnormally expressed miRNAs have pivotal roles in key pathogenic processes of microvascular complications, such as fibrosis, apoptosis, inflammation, and angiogenesis. Moreover, clinical research into innovative both diagnostic and prognostic tools suggests circulating miRNAs as possible novel noninvasive markers of diabetes microvascular complications. In this review, we summarize current knowledge and understanding of the role of miRNAs in the injury to the microvascular bed in diabetes and discuss the potential of miRNAs as clinical biomarkers of diabetes microvascular complications.

Role of the endocannabinoid system in diabetes and diabetic complications

Increasing evidence suggests that an overactive endocannabinoid system (ECS) may contribute to the development of diabetes by promoting energy intake and storage, impairing both glucose and lipid metabolism, by exerting pro-apoptotic effects in pancreatic beta cells and by facilitating inflammation in pancreatic islets. Furthermore, hyperglycaemia associated with diabetes has also been implicated in triggering perturbations of the ECS amplifying the pathological processes mentioned above, eventually culminating in a vicious circle. Compelling evidence from preclinical studies indicates that the ECS also influences diabetes-induced oxidative stress, inflammation, fibrosis and subsequent tissue injury in target organs for diabetic complications. In this review, we provide an update on the contribution of the ECS to the pathogenesis of diabetes and diabetic microvascular (retinopathy, nephropathy and neuropathy) and cardiovascular complications. The therapeutic potential of targeting the ECS is also discussed.

LINKED ARTICLES

This article is part of a themed section on Endocannabinoids. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.7/issuetoc.

Diabetes-specific variables associated with quality of life changes in young diabetic people: the type 1 diabetes Registry of Turin (Italy)

BACKGROUND AND AIMS

Type 1 diabetes (T1DM) affects young people during the most active years of their life. Our aim was to assess quality of life (QoL) and associated variables in a large cohort of adults with childhood-onset and adult-onset T1DM.

METHODS

A cohort of adult patients (18 years and older) from the T1DM Registry of Turin, Italy, was recruited. Clinical characteristics and Diabetes QoL (DQOL) questionnaire were assessed by standardized procedures.

RESULTS

310 adults completed the questionnaire. Age and diabetes duration at assessment (mean ± SD) were 32.8 ± 7.3 years and 17.3 ± 6.3 years, respectively. DQOL and its subscores were in the lower quartiles of their distributions, indicating a good level of QoL. However, scores were significantly higher in females than in males, particularly for the subscale of diabetes-related worries. In multivariate analysis, lower QoL was independently associated with female sex (β = 1.07, 95% CI 1.03-1.11, p = 0.003), higher age at onset (β = 1.03, 1.00-1.05, p = 0.009), lower schooling (β = 1.05, 1.00-1.09, p = 0.02), higher fasting plasma glucose (β = 1.03, 1.01-1.05, p = 0.008), daily SMBG >4 (β = 1.06, 1.01-1.10, p = 0.01), severe hypoglycemia over the last year (β = 1.06, 1.01-1.11, p = 0.02), lower numbers of diabetologic visits (β = 1.07, 1.01-1.13, p = 0.02) and hypertension (β = 1.06, 1.02-1.10, p = 0.005). Autonomic neuropathy was associated with diabetes impact. Female sex (β = 4.36, 2.43-7.83) and daily SMBG >4 (β = 3.77, 1.72-8.30) were independently associated with worst level and CSII with better level (β = 0.22, 0.07-0.68) of diabetes-related worries.

CONCLUSIONS

The impact of T1DM on QoL may depend on demographic, metabolic control-related variables, presence of complications and insulin delivery modality.

Hippocampal heat shock protein 25 expression in streptozotocin-induced diabetic mice

Hippocampal abnormalities are believed to increase the risk of cognitive decline in diabetic patients. The underlying mechanism is unknown, but both hyperglycemia and oxidative stress have been implicated. Cellular stresses induce the expression of heat shock protein 25 (HSP25) and this results in cytoprotection. Our aim was to assess hippocampal expression of HSP25 in experimental diabetes. Mice were rendered diabetic by streptozotocin injection. Ten weeks after diabetes onset hippocampal HSP25 expression was studied by immunoblotting and immunohistochemistry (IHC). Expression of glial fibrillary acidic protein, nitrotyrosine, iNOS, HSP72, HSP90, and Cu/Zn superoxide dismutase (SOD) was assessed by either IHC or immunoblotting, Cu/Zn-SOD activity by enzymatic assay, and malondialdehyde (MDA) content by colorimetric assay. Hippocampal HSP25 was significantly increased in diabetic as compared to non-diabetic animals and localized predominantly within the pyramidal neurons layer of the CA1 area. This was paralleled by overexpression of nitrotyrosine, iNOS, SOD expression/activity, and enhanced MDA content. In experimental diabetes, HSP25 is overexpressed in the CA1 pyramidal neurons in parallel with markers of oxidative stress.

Uric acid is not an independent predictor of cardiovascular mortality in type 2 diabetes: a population-based study

OBJECTIVE

Although some studies have suggested that uric acid is a risk factor for mortality, this relationship is still uncertain in people with type 2 diabetes.

METHODS

The study base was the population-based cohort of 1540 diabetic subjects (median age 68.9 years) of the Casale Monferrato Study. The role of serum uric acid on 15-years all-cause, cardiovascular and non-cardiovascular mortality was assessed by multivariate Cox proportional hazards modeling.

RESULTS

Baseline levels of serum uric acid were negatively correlated with HbA1c, were higher in men and in the elderly and were independently associated with components of the metabolic syndrome. Out of 14,179 person-years, 1000 deaths (514 due to cardiovascular diseases) were observed. Compared to the lower quartile of uric acid, HRs (95% CI) in the upper quartile were 1.47 (1.22-1.76) for all-cause mortality; 1.40 (1.09-1.80) for cardiovascular mortality and 1.50 (1.15-1.96) for non-cardiovascular mortality. In multiple adjusted models, however, HRs were 1.30 (1.06-1.60) for all-cause mortality, 1.13 (0.85-1.50) for cardiovascular mortality and 1.50 (1.11-2.02) for non-cardiovascular mortality (men 1.87, 1.19-2.95; women 1.20, 0.80-1.80); the latter appeared to be due to neoplastic diseases (HR in all combined quartiles vs. lower quartile: both sexes 1.59, 1.05-2.40; men 1.54, 0.83-2.84, women 1.68, 0.95-2.92).

CONCLUSIONS

In diabetic people, uric acid is associated with components of the metabolic syndrome but it may not be accounted as an independent risk factor for cardiovascular mortality. The increased all-cause mortality risk with higher levels of uric acid might be due to increased neoplastic mortality and deserves future studies.

Aortopulmonary window and double aortic arch. A rare association

We report the case of a 27-year-old male patient with dyspnea on physical exertion. Clinical assessment and various tests led to the diagnosis of aortopulmonary window and double aortic arch. According to a literature search, this may be the first report on such association.