Osteopontin in diabetic nephropathy: signpost or road?

Single-cell transcriptomic profiles in the pathophysiology within the microenvironment of early diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage kidney disease, resulting in a huge socio-economic impact. Kidney is a highly complex organ and the pathogenesis underlying kidney organization involves complex cell-to-cell interaction within the heterogeneous kidney milieu. Advanced single-cell RNA sequencing (scRNA-seq) could reveal the complex architecture and interaction with the microenvironment in early DKD. We used scRNA-seq to investigate early changes in the kidney of db/m mice and db/db mice at the 14th week. Uniform Manifold Approximation and Projection were applied to classify cells into different clusters at a proper resolution. Weighted gene co-expression network analysis was used to identify the key molecules specifically expressed in kidney tubules. Information of cell-cell communication within the kidney was obtained using receptor-ligand pairing resources. In vitro model, human subjects, and co-detection by indexing staining were used to identify the pathophysiologic role of the hub genes in DKD. Among four distinct subsets of the proximal tubule (PT), lower percentages of proliferative PT and PT containing AQP4 expression (PT^AQP4+) in db/db mice induced impaired cell repair activity and dysfunction of renin-angiotensin system modulation in early DKD. We found that ferroptosis was involved in DKD progression, and ceruloplasmin acted as a central regulator of the induction of ferroptosis in PT^AQP4+. In addition, lower percentages of thick ascending limbs and collecting ducts with impaired metabolism function were also critical pathogenic features in the kidney of db/db mice. Secreted phosphoprotein 1 (SPP1) mediated pathogenic cross-talk in the tubular microenvironment, as validated by a correlation between urinary SPP1/Cr level and tubular injury. Finally, mesangial cell-derived semaphorin 3C (SEMA3C) further promoted endothelium-mesenchymal transition in glomerular endothelial cells through NRP1 and NRP2, and urinary SEMA3C/Cr level was positively correlated with glomerular injury. These data identified the hub genes involved in pathophysiologic changes within the microenvironment of early DKD.

Association of osteopontin with kidney function and kidney failure in chronic kidney disease patients: the GCKD study

BACKGROUND

Osteopontin (OPN), synthesized in the thick ascending limb of Henle's loop and in the distal tubule, is involved in the pathogenesis of kidney fibrosis, a hallmark of kidney failure (KF). In a cohort of chronic kidney disease (CKD) patients, we evaluated OPN's association with kidney markers and KF.

METHODS

OPN was measured from baseline serum samples of German Chronic Kidney Disease study participants. Cross-sectional regression models for estimated glomerular filtration rate (eGFR) and urinary albumin-to-creatinine ratio (UACR) as well as Cox regression models for all-cause mortality and KF were evaluated to estimate the OPN effect. Additionally, predictive ability, of OPN and time-dependent population-attributable fraction were evaluated.

RESULTS

Over a median follow-up of 6.5 years, 471 KF events and 629 deaths occurred among 4,950 CKD patients. One-unit higher log(OPN) was associated with 5.5 mL/min/1.73m2 lower eGFR (95%CI: [-6.4,-4.6]) and 1% change in OPN with 0.7% higher UACR (estimated effect 0.7, 95%CI: [0.6,0.8]). Moreover, higher OPN levels were associated with a higher risk of KF (hazard ratio [HR] 1.4, 95%CI: [1.2,1.7]) and all-cause mortality (HR 1.5, 95%CI: [1.3,1.8]). After 6 years, 31% of the KF events could be attributed to higher OPN levels (95%CI: [3%,56%]).

CONCLUSIONS

In this study, higher OPN levels were associated with kidney function markers worsening, and a higher risk for adverse outcomes. A larger proportion of KF could be attributed to higher OPN levels warranting further research on OPN with regards to its role in CKD progression and possible treatment options.

Association of Salivary Osteopontin Levels with Glycaemic Status and Microalbuminuria - in Patients with Type 2 Diabetes Mellitus

INTRODUCTION

The monitoring of glycaemic status in patients with T2DM is mainly through blood tests (Fasting plasma glucose and HbA1c), which are invasive and involves painful pricks. This leads to poor patient compliance and soon could lead to various micro and macro vascular complications, which hamper the quality of life. There are no sensitive and specific markers to predict these complications at the earliest. Sialochemistry has recently gained attention for monitoring chronic diseases. Osteopontin is a phospho-glycoprotein molecule, elevated in many inflammatory conditions.

AIM

The aim of the study was to evaluate the role of serum and salivary osteopontin in Type 2 Diabetes mellitus (T2DM).

MATERIALS AND METHODS

In this case-control study, we recruited 33 cases of T2DM and 31 age and gender matched healthy controls. Body Mass Index (BMI), Waist/Hip Ratio (WHR), Waist Circumference (WC) and blood pressure was recorded. Fasting Plasma Glucose (FPG), salivary glucose, HbA1c, microalbuminuria, systolic BP, serum and salivary osteopontin levels were estimated.

RESULTS

FPG, salivary glucose, HbA1c, microalbuminuria, systolic BP, BMI, waist / hip ratio serum and salivary osteopontin levels were significantly high in T2DM cases compared to control subjects. Serum and salivary osteopontin levels were significantly correlated with HbA1c and microalbuminuria in T2DM cases.

CONCLUSION

Serum and salivary osteopontin levels are significantly elevated in subjects with T2DM and are associated with glycaemic control and microalbuminuria.

Association between Osteopontin Promoter Gene Polymorphisms and Haplotypes with Risk of Diabetic Nephropathy

Background: Osteopontin (OPN) C-443T promoter polymorphism has been shown as a genetic risk factor for diabetic nephropathy (DN) in type 2 diabetic patients (T2D). Methods: In the present study we investigated the association of three functional promoter gene polymorphisms C-443T, delG-156G, and G-66T and their haplotypes with the risk of DN and estimated Glomerular Filtration Rate (eGFR) in Asian Indians T2D patients using Real time PCR based Taqman assay. A total of 1165 T2D patients, belonging to two independently ascertained Indian Asian cohorts, were genotyped for three OPN promoter polymorphisms C-443T (rs11730582), delG-156G (rs17524488) and G-66T (rs28357094). Results: -156G allele and GG genotypes (delG-156G) and haplotypes G-C-G and T-C-G (G-66T, C-443T, delG-156G) were associated with decreased risk of DN and higher eGFR. Haplotype G-T-delG and T-T-delG (G-66T, C-443T, delG-156G) were identified as risk haplotypes, as shown by lower eGFR. Conclusion: This is the first study to report an association of OPN promoter gene polymorphisms; G-66T and delG-156G and their haplotypes with DN in T2D. Our results suggest an association between OPN promoter gene polymorphisms and their haplotypes with DN.

Urinary OPN excretion in children with glomerular proteinuria

PURPOSE

The aim of the study was to investigate urinary levels and clinical significance of osteopontin (uOPN) in children with different glomerular diseases according to histological diagnosis and degree of proteinuria.

MATERIALS AND METHODS

The examinations were conducted in 3 groups of children: I - 20 children with minimal change disease (MCD) examined twice: A - in relapse; B - in remission, group II - 17 children with focal segmental glomerulosclerosis (FSGS), III - 12 children with IgA nephropathy (IgAN). The control group (C) contained 20 healthy children. OPN was measured in the urine using ELISA commercial available kit (R&D Quantikine) and was expressed in ng/ mg cr.

RESULTS

The median uOPN/ cr. in MCD children in relapse (IA) was median 134.98 ng/ mg cr. and was higher when compared to controls (p< 0.01). In exam IB, when proteinuria subsided, OPN/ cr. increased to median 172.96 ng/ mg cr. and was higher in comparison to healthy subjects (p< 0.01) and MCD children in relapse (p<0.05). Children from group II revealed higher uOPN/ cr. levels when compared to groups I, III and C (p< 0.01). UOPN/ cr. positively correlated with protein/ creatinine ratio in all examined groups of children (p< 0.01).

CONCLUSION

We found significantly higher uOPN/ cr. in all the groups of children with glomerulonephritis. The highest uOPN/ cr. levels were found in patients with FSGS and correlated significantly with both interstitial changes and mesangial expansion found in kidney biopsy.