Proteolysis of insulin-like growth factor-binding protein-3 is increased in urine from patients with diabetic nephropathy

Impaired kidney structure and function in spinal muscular atrophy

Objective

To determine changes in serum profiles and kidney tissues from patients with spinal muscular atrophy (SMA) type 1 compared with age- and sex-matched controls.

Methods

In this cohort study, we investigated renal structure and function in infants and children with SMA type 1 in comparison with age- and sex-matched controls.

Results

Patients with SMA had alterations in serum creatinine, cystatin C, sodium, glucose, and calcium concentrations, granular casts and crystals in urine, and nephrocalcinosis and fibrosis. Nephrotoxicity and polycystic kidney disease PCR arrays revealed multiple differentially expressed genes, and immunoblot analysis showed decreased calcium-sensing receptors and calbindin and increased insulin-like growth factor-binding proteins in kidneys from patients with SMA.

Conclusions

These findings demonstrate that patients with SMA type 1, in the absence of disease-modifying therapies, frequently manifest impaired renal function as a primary or secondary consequence of their disease. This study provides new insights into systemic contributions to SMA disease pathogenesis and the need to identify coadjuvant therapies.

Role of Receptor Tyrosine Kinase Signaling in Renal Fibrosis

Renal fibrosis can be induced in different renal diseases, but ultimately progresses to end stage renal disease. Although the pathophysiologic process of renal fibrosis have not been fully elucidated, it is characterized by glomerulosclerosis and/or tubular interstitial fibrosis, and is believed to be caused by the proliferation of renal inherent cells, including glomerular epithelial cells, mesangial cells, and endothelial cells, along with defective kidney repair, renal interstitial fibroblasts activation, and extracellular matrix deposition. Receptor tyrosine kinases (RTKs) regulate a variety of cell physiological processes, including metabolism, growth, differentiation, and survival. Many studies from in vitro and animal models have provided evidence that RTKs play important roles in the pathogenic process of renal fibrosis. It is also showed that tyrosine kinases inhibitors (TKIs) have anti-fibrotic effects in basic research and clinical trials. In this review, we summarize the evidence for involvement of specific RTKs in renal fibrosis process and the employment of TKIs as a therapeutic approach for renal fibrosis.

The Application of SILAC Mouse in Human Body Fluid Proteomics Analysis Reveals Protein Patterns Associated with IgA Nephropathy

Body fluid proteome is the most informative proteome from a medical viewpoint. But the lack of accurate quantitation method for complicated body fluid limited its application in disease research and biomarker discovery. To address this problem, we introduced a novel strategy, in which SILAC-labeled mouse serum was used as internal standard for human serum and urine proteome analysis. The SILAC-labeled mouse serum was mixed with human serum and urine, and multidimensional separation coupled with tandem mass spectrometry (IEF-LC-MS/MS) analysis was performed. The shared peptides between two species were quantified by their SILAC pairs, and the human-only peptides were quantified by mouse peptides with coelution. The comparison for the results from two replicate experiments indicated the high repeatability of our strategy. Then the urine from Immunoglobulin A nephropathy patients treated and untreated was compared by this quantitation strategy. Fifty-three peptides were found to be significantly changed between two groups, including both known diagnostic markers for IgAN and novel candidates, such as Complement C3, Albumin, VDBP, ApoA,1 and IGFBP7. In conclusion, we have developed a practical and accurate quantitation strategy for comparison of complicated human body fluid proteome. The results from such strategy could provide potential disease-related biomarkers for evaluation of treatment.

The insulin-like growth factor system in chronic kidney disease: Pathophysiology and therapeutic opportunities

The growth hormone-insulin-like growth factor-insulin-like growth factor binding protein (GH-IGF-IGFBP) axis plays a critical role in the maintenance of normal renal function and the pathogenesis and progression of chronic kidney disease (CKD). Serum IGF-I and IGFBPs are altered with different stages of CKD, the speed of onset, the amount of proteinuria, and the potential of remission. Recent studies demonstrate that growth failure in children with CKD is due to a relative GH insensitivity and functional IGF deficiency. The functional IGF deficiency in CKD results from either IGF resistance due to increased circulating levels of IGFBPs or IGF deficiency due to increased urinary excretion of serum IGF-IGFBP complexes. In addition, not only GH and IGFs in circulation, but locally produced IGFs, the high-affinity IGFBPs, and low-affinity insulin-like growth factor binding protein-related proteins (IGFBP-rPs) may also affect the kidney. With respect to diabetic kidney disease, there is growing evidence suggesting that GH, IGF-I, and IGFBPs are involved in the pathogenesis of diabetic nephropathy (DN). Thus, prevention of GH action by blockade either at the receptor level or along its signal transduction pathway offers the potential for effective therapeutic opportunities. Similarly, interrupting IGF-I and IGFBP actions also may offer a way to inhibit the development or progression of DN. Furthermore, it is well accepted that the systemic inflammatory response is a key player for progression of CKD, and how to prevent and treat this response is currently of great interest. Recent studies demonstrate existence of IGF-independent actions of high-affinity and low-affinity-IGFBPs, in particular, antiinflammatory action of IGFBP-3 and profibrotic action of IGFBP-rP2/CTGF. These findings reinforce the concept in support of the clinical significance of the IGF-independent action of IGFBPs in the assessment of pathophysiology of kidney disease and its therapeutic potential for CKD. Further understanding of GH-IGF-IGFBP etiopathophysiology in CKD may lead to the development of therapeutic strategies for this devastating disease. It would hold promise to use of GH, somatostatin analogs, IGFs, IGF agonists, GHR and insulin-like growth factor-I receptor (IGF-IR) antagonists, IGFBP displacer, and IGFBP antagonists as well as a combination treatment as therapeutic agents for CKD.

Inadequate diabetic care: global figures cry for preventive measures and personalized treatment

Diabetes mellitus (DM) is a lifelong progressive disease. Currently there are more than 285 million DM-affected people worldwide. Globally the prevalence of diabetes continues to rise and is more pronounced in countries with large populations such as China, India and USA. Driving forces behind the epidemic are obesity, aging of the population and longer life expency. Prospective, the majority of diabetic population will be in their six to eight decades of life with the implication of more females than males. Severe micro- and macrovascular complications associated with diabetes lead to a highly increased morbidity and mortality. Therefore, DM is projected to be one of the leading health problems of 21st centuary. Urgent measures are required to reduce the diabetic burden. Thus advanced predictive diagnostic tools and personalized treatment strategies in (pre)diabetic care are critical and should exert beneficial impact on public health.

Novel roles of the IGF-IGFBP axis in etiopathophysiology of diabetic nephropathy

Mechanisms contributing to development of diabetic nephropathy (DN) remain unclear. High ambient glucose level transforms intracellular pathways, promoting stable phenotypic changes in the glomerulus such as mesangial cell hypertrophy, podocyte apoptosis, and matrix expansion. Insulin-like growth factors (IGFs) and the high affinity IGF binding proteins (IGFBPs) exert major effects on cell growth and metabolism. Compared with diabetic patients without microalbuminuria (MA), MA diabetic patients display perturbed GH-IGF-IGFBP homeostasis, including increased circulating IGF-I and IGFBP-3 protease activity, increased excretion of bioactive GH, IGF-I, and IGFBP-3, but decreased circulating IGFBP-3 levels. In diabetic animal models, expression of IGF-I and IGFBP-1 to -4 increases in key renal tissues and glomerular ulrafiltrate. Epithelial, mesangial, and endothelial cells derived from the kidney respond to IGF-I binding with increased protein synthesis, migration, and proliferation. This article reviews classic and emerging concepts for the roles of the GH-IGF-IGFBP axis in the etiopathophysiology, treatment, and prevention of diabetic renal disease. We report IGF-independent actions of IGFBP-3 in the podocyte for the first time.

Identification and purification from the plasma of Type 1 diabetic subjects of a proteolytically active Grp94Evidence that Grp94 is entirely responsible for plasma proteolytic activity

AIMS/HYPOTHESIS

The overall increase in proteolytic activity in diabetes is known to be associated with the development and progression of vascular complications. Our aim was to investigate in detail the molecular nature of this activity in the plasma of Type 1 diabetic subjects.

METHODS

Plasma of both diabetic and control subjects was subjected to various purification procedures (ion exchange and affinity chromatography, HPLC, immunoprecipitation, electrophoresis, immunoblot and mass analyses) to identify the proteins of interest. Biological activities were measured on specific substrates.

RESULTS

In diabetic but not normal plasma we identified the presence of two heat shock proteins, Grp94 (Glucose-regulated protein94) and HSP70. The higher-than-normal proteolytic activity of Grp94 was: (i) directed against casein, but not against endogenous plasma proteins; (ii) fully and specifically inhibited only by anti-Grp94 polyclonal antibodies; and (iii) coupled with low-level ATPase activity. In addition, ATP binding to Grp94 was able to modulate proteolytic activity. We found that Grp94 in plasma circulates only as high molecular mass homo- and hetero-complexes, the latter mostly formed with IgG to which Grp94 is also linked by tenacious binding. Proteolytically-active Grp94 was purified by immunoprecipitation, which co-immunoprecipitated alpha(1)antitrypsin.

CONCLUSION/INTERPRETATION

Our results show the unexpected extracellular location and characteristic biological function of Grp94 even at a late stage of disease. These findings have physiopathological relevance for predicting activation of both autoimmune and inflammatory processes potentially associated with vascular complications.