Localization of glutamic acid decarboxylase in the kidneys of nonobese diabetic mice

In silico design, synthesis, characterization and pharmacological evaluation of captopril conjugates in the treatment of renal fibrosis

Application of glutamic acid and taurine conjugates of captopril for kidney targeting.

Expression and localization of VIAAT in distal uriniferous tubular epithelium of mouse

Vesicular inhibitory amino acid transporter (VIAAT) is a transmembrane transporter which is responsible for the storage of gamma-aminobutyric acid (GABA) or glycine in synaptic vesicles. According to recent studies, GABA is known to be expressed in the kidney. For clear understanding of the intra-renal GABA signaling, the localization of VIAAT was examined in the present study. Intense immunoreactivity was found largely confined to the distal tubule epithelia, especially distinct in the inner medulla, although the immunoreactivity was discerned more or less in all tubules and glomeruli. No distinct immunoreactivity was seen in capillary endothelia or interstitial fibroblasts. In immuno-DAB and immuno-gold electron microscopy, the immunoreaction was found at the basal infoldings of plasma membranes and basal portions of the lateral plasma membranes, but not in any vesicles or vacuoles within the distal tubular cells. The significance of the enigmatic finding, localization of a vesicular molecule on selected portions of the plasma membrane of distal tubular cells, was discussed in view of the possibility of paracrine or autocrine effects of GABA on some other uriniferous tubular cells or interstitial cells.

Characteristic expressions of GABA receptors and GABA producing/transporting molecules in rat kidney

Gamma-aminobutyric acid (GABA) is an important neurotransmitter, but recent reports have revealed the expression of GABAergic components in peripheral, non-neural tissues. GABA administration induces natriuresis and lowers blood pressure, suggesting renal GABA targets. However, systematic evaluation of renal GABAergic components has not been reported. In this study, kidney cortices of Wistar-Kyoto rats (WKY) were used to assay for messenger RNAs of GABA-related molecules using RT-PCR. In WKY kidney cortex, GABA_A receptor subunits, α1, β3, δ, ε and π, in addition to both types of GABA_B receptors, R1 and R2, and GABA_C receptor ρ1 and ρ2 subunit mRNAs were detected. Kidney cortex also expressed mRNAs of glutamate decarboxylase (GAD) 65, GAD67, 4-aminobutyrate aminotransferase and GABA transporter, GAT2. Western blot and/or immunohistochemistry were performed for those molecules detected by RT-PCR. By immunofluorescent observation, co-staining of α1, β3, and π subunits was observed mainly on the apical side of cortical tubules, and immunoblot of kidney protein precipitated with π subunit antibody revealed α1 and β3 subunit co-assembly. This is the first report of GABA_A receptor π subunit in the kidney. In summary, unique set of GABA receptor subunits and subtypes were found in rat kidney cortex. As GABA producing enzymes, transporters and degrading enzyme were also detected, a possible existence of local renal GABAergic system with an autocrine/paracrine mechanism is suggested.

T Cell Epitope Mimicry in Antiglomerular Basement Membrane Disease

Antiglomerular basement membrane (GBM) disease or Goodpasture's syndrome is among the earliest recognized human autoimmune diseases. Although collagen 4alpha3 NC1 (Col4alpha3NC1) has been identified as the responsible autoantigen, it remains unknown how autoimmunity to this autoantigen is provoked. We have demonstrated in our rat model that a single nephritogenic T cell epitope pCol28-40 of Col4alpha3NC1 induces glomerulonephritis. We hypothesized that microbial peptides that mimic this T cell epitope could induce the disease. Based on the critical residue motif (xxtTxNPsxx) of pCol28-40, seven peptides derived from human infection-related microbes were chosen through GenBank search and synthesized. All peptides showed cross-reactivity with pCol28-40-specific T cells at various levels. Only four peptides induced transient proteinuria and minor glomerular injury. However, the other three peptides induced severe proteinuria and modest to severe glomerulonephritis in 16-25% of the immunized rats. Unexpectedly, the most nephritogenic peptide, pCB, derived from Clostridium botulinum, also induced modest (25%) to severe (25%) pulmonary hemorrhage, another important feature of anti-GBM disease; this was not correlated with the severity of glomerulonephritis. This finding suggests that subtle variations in T cell epitope specificity may lead to different clinical manifestations of anti-GBM disease. In summary, our study raises the possibility that a single T cell epitope mimicry by microbial Ag may be sufficient to induce the anti-GBM disease.

Use of genetic mouse models in the study of diabetic nephropathy

The study of experimental diabetic nephropathy in rodent models has led to many changes in the clinical management of human diabetic nephropathy. With the development of technology to generate knockout and transgenic animals, the mouse has become a favored species in medical research. There are several genetic mouse models of diabetes, with the majority being models of type 2 diabetes mellitus. These include the hypoinsulinemic nonobese diabetic mouse, the KKAy mouse, the New Zealand obese mouse, the hyperinsulinemic ob/ob mouse, and the different strains of obese hyperinsulinemic db/db mouse. Each of these models displays some renal changes, but by far the best model of renal disease and the one that is the most studied is the db/db mouse. The db/db mouse displays substantial glomerular pathology, including mesangial matrix expansion and modest albuminuria. It has been reported that the db/db mouse has a decline in creatinine clearance after 5 months of age, but more specific approaches are warranted to confirm these findings. A number of intervention studies show renoprotection in this model. Although mice have many advantages, such as being able to be crossbred with genetically manipulated animals, in many ways they are not very similar to humans, and in some respects the rat may be a better choice, particularly in relation to some features of end-organ injury.

Use of genetic mouse models in the study of diabetic nephropathy

The study of experimental diabetic nephropathy in rodent models has led to many changes in the clinical management of human diabetic nephropathy. With the development of technology to generate knockout and transgenic animals, the mouse has become a favored species in medical research. There are several genetic mouse models of diabetes, with the majority being models of type 2 diabetes mellitus. These include the hypoinsulinemic non-obese diabetic mouse, the Kkay mouse, the New Zealand obese mouse, the hyperinsulinemic ob/ob mouse, and the different strains of obese hyperinsulinemic db/db mouse. Each of these models displays some renal changes, but by far the best model of renal disease and the one that is the most studied is the db/db mouse. The db/db mouse displays substantial glomerular pathology, including mesangial matrix expansion and modest albuminuria. It has been reported that the db/db mouse has a decline in creatinine clearance after 5 months of age, but more specific approaches are warranted to confirm these findings. A number of intervention studies show renoprotection in this model. Although mice have many advantages, such as being able to be cross-bred with genetically manipulated animals, in many ways they are not very similar to humans, and in some respects the rat may be a better choice, particularly in relation to some features of end-organ injury.

Human fibroblasts ubiquitously express glutamic acid decarboxylase 65 (GAD 65): possible effects of connective tissue inflammation on GAD antibody titer

BACKGROUND

Type 1 diabetes is caused by a destruction of pancreatic beta cells due to autoimmunity. Autoantibody against glutamic acid decarboxylase (GAD) 65 expressed in pancreatic beta cells is widely used as a predictive marker for pancreatic destruction. In this study, we hypothesized that if certain cells in periodontal tissues could express GAD, then it may influence GAD antibody titer.

METHODS

We used: 1) reverse transcription-polymerase chain reaction (PCR) analysis to detect GAD 65 mRNA in various cells; 2) nucleotide sequencing analysis to confirm that amplified PCR product is the gene encoding GAD; and 3) Western blotting to determine the expression of GAD 65 protein in human gingival fibroblasts. Immunohistochemical staining of GAD 65 protein in normal and inflamed gingiva was performed to examine the potential influence of periodontal inflammation on GAD 65 expression. GAD antibody titer in sera of periodontal patients as well as healthy subjects was measured to determine if periodontal patients could develop autoantibody against GAD 65.

RESULTS

Cultured human gingival, periodontal, and dermal fibroblasts and mesangial cells expressed GAD mRNA. Nucleotide sequencing analyses confirmed the amplified PCR product as GAD 65. Western immunoblotting analyses and immunohistochemical staining revealed that the GAD 65 protein was expressed in vitro and in vivo. The expression of GAD 65 in inflamed tissue was higher than that in normal tissues. Two of 62 periodontal patients without diabetes showed an increased antibody titer against GAD 65, while none of the systemically healthy subjects showed an increased antibody titer against this antigen.

CONCLUSIONS

We concluded that periodontal inflammation may result in higher levels of GAD and influence GAD antibody titer, and, hence, affect diabetic diagnosis based upon GAD antibody production.

Dynamic expression of a glutamate decarboxylase gene in multiple non-neural tissues during mouse development

BACKGROUND

Glutamate decarboxylase (GAD) is the biosynthetic enzyme for the neurotransmitter gamma-aminobutyric acid (GABA). Mouse embryos lacking the 67-kDa isoform of GAD (encoded by the Gad1 gene) develop a complete cleft of the secondary palate. This phenotype suggests that this gene may be involved in the normal development of tissues outside of the CNS. Although Gad1 expression in adult non-CNS tissues has been noted previously, no systematic analysis of its embryonic expression outside of the nervous system has been performed. The objective of this study was to define additional structures outside of the central nervous system that express Gad1, indicating those structures that may require its function for normal development.

RESULTS

Our analysis detected the localized expression of Gad1 transcripts in several developing tissues in the mouse embryo from E9.0-E14.5. Tissues expressing Gad1 included the tail bud mesenchyme, the pharyngeal pouches and arches, the ectodermal placodes of the developing vibrissae, and the apical ectodermal ridge (AER), mesenchyme and ectoderm of the limb buds.

CONCLUSIONS

Some of the sites of Gad1 expression are tissues that emit signals required for patterning and differentiation (AER, vibrissal placodes). Other sites correspond to proliferating stem cell populations that give rise to multiple differentiated tissues (tail bud mesenchyme, pharyngeal endoderm and mesenchyme). The dynamic expression of Gad1 in such tissues suggests a wider role for GABA signaling in development than was previously appreciated.

Localization of cells preferentially expressing GAD(67) with negligible GAD(65) transcripts in the rat hippocampus. A double in situ hybridization study

Two major forms of glutamic acid decarboxylase (GAD) are present in the mammalian brain, a 65-kDa isoform (GAD(65)) and a 67-kDa isoform (GAD(67)), and it is usually assumed that all GABAergic neurons contain both. The two forms have not yet been colocalized to the same neurons, because the GAD(65) protein is found almost exclusively in axon terminals, while GAD(67) is found predominantly in the cell body. Using double in situ hybridization (DISH) with both radioactive [35S] and non-radioactive (digoxigenin, DIG) probes, the distributions of GAD(65) and GAD(67) mRNA have been simultaneously examined in the rat hippocampus. The results suggest that [35S] radioprobes are slightly more sensitive than DIG probes, and that the reversal of labels is necessary in DISH studies to determine whether a neuronal subtype which expresses only one isoform of GAD may be present. The data indicate that the majority of cells (90%) showing labeling were labeled for both GAD(65) and GAD(67) mRNA. In sectors CA1 and CA3 approximately 5-10% of the cells positive for GAD(67) showed little or no detectable GAD(65) mRNA. In the hilus, however, GAD(65) levels were higher, and all cells seem to express both GAD(65) and GAD(67) mRNA. Taken together, these results support the view that most GABAergic neurons in the hippocampus express both GAD(65) and GAD(67). However, it appears that some interneurons in the CA subfields differ from "classic" GABAergic interneurons by preferentially expressing the 67-kDa isoform of GAD under baseline conditions, with GAD(65) mRNA levels very low or absent.

An endogenous activator of renal glutamic acid decarboxylase effects of adenosine triphosphate, phosphate and chloride on the activity of this enzyme

The renal glutamic acid decarboxylase (GAD) differs from the brain and pancreatic enzyme by its strong binding to membranes that is not influenced by detergents. After centrifugation of freshly prepared homogenate of the rat renal cortex, only 10-15% of GAD activity was found in supernatants and 15-30% in pellets. The majority of the GAD activity was lost. The bound GAD was found in the pellet. A thermolabile activator was present in the supernatant, which was not lost on dialysis. Approximately 55% of the total GAD activity was solubilized in homogenates stored for 24 h at 4 degrees C without detergent, whereas in homogenates stored with Triton X-100, the solubilized GAD increased to 80%. This solubilization was decreased by inhibitors of thioproteases such as leupeptin, antipain and trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E-64). Solubilized GAD was applied to DEAE Toyopearl resin and the GAD activator was eluted with 35 mM Pi. GAD was eluted with 250 mM Pi. The effect of ATP on the activity of renal GAD was also different to its effect on brain GAD. ATP is a strong inhibitor of the brain enzyme at physiological concentrations. ATP (and Pi), together with chlorides (another brain GAD inhibitor), stabilize the renal GAD. However, renal GAD was inhibited by ATP in the presence of leupeptin in freshly prepared homogenates. Similarly, ATP inhibits solubilized GAD from homogenates stored without Triton X-100 for 24 h at 4 degrees C, but Pi retains its stabilizing effect in this preparation. A significant finding of the work presented here is the obligatory requirement of an endogenous activator for renal GAD activity. Whether this activator is an enzyme converting the inactive GAD to active enzyme (as hypothesized for brain GAD), or whether it is a protein affecting the activity of renal GAD by binding (as observed for GAD in some plants) remains to be established.