Marginal Zone B (MZB) Cells: Comparison of the Initial Identification of Immune Activity Leading to Dacryoadenitis and Sialadenitis in Experimental Sjögren's Syndrome.

Although multiple mouse strains have been advanced as models for Sjögren's syndrome (SS), which is a human systemic autoimmune disease characterized primarily as the loss of lacrimal and salivary gland functions, the C57BL/6.NOD-Aec1Aec2 recombinant inbred (RI) mouse derived from the NOD/ShiLtJ line is considered one of the more appropriate models exhibiting virtually all the characteristics of the human disease. This mouse model, as well as other mouse models of SS, have shown that B lymphocytes are essential for the onset and development of observed clinical manifestations. Recently, studies carried out in the C57BL/6.IL14α transgenic mouse have provided clear evidence that the marginal zone B (MZB) cell population is directly involved in the early pathological events initiating the development of the clinical SS disease, as well as late-stage lymphomagenesis resulting in B-cell lymphomas. Since MZB cells are difficult to study in vivo and in vitro, we carried out a series of ex vivo investigations that utilize temporal global RNA transcriptomic analyses to profile differentially expressed genes exhibiting temporal upregulation during the initial onset and subsequent development of pathophysiological events within the lacrimal and salivary gland tissues per se or associated with the leukocyte cell migrations into these glands. The initial transcriptomic analyses revealed that while the upregulated gene expression profiles obtained from lacrimal and salivary glands overlap, multiple genetic differences exist between the defined activated pathways. In the current study, we present a concept suggesting that the initial pathological events differ between the two glands, yet the subsequent upregulated TLR4/TLR3 signal transduction pathway that activates the type-1 interferon signature appears to be identical in the two glands and indicates an autoimmune response against dsRNA, possibly a virus. Here, we attempt to put these findings into perspective and determine how they can impact the design of future therapeutic protocols.

A Temporal Comparative RNA Transcriptome Profile of the Annexin Gene Family in the Salivary versus Lacrimal Glands of the Sjögren's Syndrome-Susceptible C57BL/6.NOD-Aec1Aec2 Mouse.

A generally accepted hypothesis for the initial activation of an immune or autoimmune response argues that alarmins are released from injured, dying and/or activated immune cells, and these products complex with receptors that activate signal transduction pathways and recruit immune cells to the site of injury where the recruited cells are stimulated to initiate immune and/or cellular repair responses. While there are multiple diverse families of alarmins such as interleukins (IL), heat-shock proteins (HSP), Toll-like receptors (TLR), plus individual molecular entities such as Galectin-3, Calreticulin, Thymosin, alpha-Defensin-1, RAGE, and Interferon-1, one phylogenetically conserved family are the Annexin proteins known to promote an extensive range of biomolecular and cellular products that can directly and indirectly regulate inflammation and immune activities. For the present report, we examined the temporal expression profiles of the 12 mammalian annexin genes (Anxa1-11 and Anxa13), applying our temporal genome-wide transcriptome analyses of ex vivo salivary and lacrimal glands from our C57BL/6.NOD-Aec1Aec2 mouse model of Sjögren's Syndrome (SS), a human autoimmune disease characterized primarily by severe dry mouth and dry eye symptoms. Results indicate that annexin genes Anax1-7 and -11 exhibited upregulated expressions and the initial timing for these upregulations occurred as early as 8 weeks of age and prior to any covert signs of a SS-like disease. While the profiles of the two glands were similar, they were not identical, suggesting the possibility that the SS-like disease may not be uniform in the two glands. Nevertheless, this early pre-clinical and concomitant upregulated expression of this specific set of alarmins within the immune-targeted organs represents a potential target for identifying the pre-clinical stage in human SS as well, a fact that would clearly impact future interventions and therapeutic strategies.

A MZB Cell Activation Profile Present in the Lacrimal Glands of Sjögren's Syndrome-Susceptible C57BL/6.NOD-Aec1Aec2 Mice Defined by Global RNA Transcriptomic Analyses.

The C57BL/6.NOD-Aec1Aec2 mouse has been extensively studied to define the underlying cellular and molecular basis for the onset and development of Sjögren's syndrome (SS), a human systemic autoimmune disease characterized clinically as the loss of normal lacrimal and salivary gland functions leading respectively to dry eye and dry mouth pathologies. While an overwhelming majority of SS studies in both humans and rodent models have long focused primarily on pathophysiological events and the potential role of T lymphocytes in these events, recent studies in our murine models have indicated that marginal zone B (MZB) lymphocytes are critical for both development and onset of SS disease. Although migration and function of MZB cells are difficult to study in vivo and in vitro, we have carried out ex vivo investigations that use temporal global RNA transcriptomic analyses to track early cellular and molecular events in these exocrine glands of C57BL/6.NOD-Aec1Aec2 mice. In the present report, genome-wide transcriptome analyses of lacrimal glands indicate that genes and gene-sets temporally upregulated during early onset of disease define the Notch2/NF-kß14 and Type1 interferon signal transduction pathways, as well as identify chemokines, especially Cxcl13, and Rho-GTPases, including DOCK molecules, in the cellular migration of immune cells to the lacrimal glands. We discuss how the current results compare with our recently published salivary gland data obtained from similar studies carried out in our C57BL/6.NOD-Aec1Aec2 mice, pointing out both similarities and differences in the etiopathogeneses underlying the autoimmune response within the two glands. Overall, this study uses the power of transcriptomic analyses to identify temporal molecular bioprocesses activated during the preclinical covert pathogenic stage(s) of SS disease and how these findings may impact future intervention therapies as the disease within the two exocrine glands may not be identical.

Upregulated Chemokine and Rho-GTPase Genes Define Immune Cell Emigration into Salivary Glands of Sjögren's Syndrome-Susceptible C57BL/6.NOD-Aec1Aec2 Mice.

The C57BL/6.NOD-Aec1Aec2 mouse is considered a highly appropriate model of Sjögren's Syndrome (SS), a human systemic autoimmune disease characterized primarily as the loss of lacrimal and salivary gland functions. This mouse model, as well as other mouse models of SS, have shown that B lymphocytes are essential for the development and onset of observed clinical manifestations. More recently, studies carried out in the C57BL/6.IL14α transgenic mouse have indicated that the marginal zone B (MZB) cell population is responsible for development of SS disease, reflecting recent observations that MZB cells are present in the salivary glands of SS patients and most likely initiate the subsequent loss of exocrine functions. Although MZB cells are difficult to study in vivo and in vitro, we have carried out an ex vivo investigation that uses temporal global RNA transcriptomic analyses to profile differentially expressed genes known to be associated with cell migration. Results indicate a temporal upregulation of specific chemokine, chemokine receptor, and Rho-GTPase genes in the salivary glands of C57BL/6.NOD-Aec1Aec2 mice that correlate with the early appearance of periductal lymphocyte infiltrations. Using the power of transcriptomic analyses to better define the genetic profile of lymphocytic emigration into the salivary glands of SS mice, new insights into the underlying mechanisms of SS disease development and onset begin to come into focus, thereby establishing a foundation for further in-depth and novel investigations of the covert and early overt phases of SS disease at the cellular level.

Early Covert Appearance of Marginal Zone B Cells in Salivary Glands of Sjögren's Syndrome-Susceptible Mice: Initiators of Subsequent Overt Clinical Disease.

The C57BL/6.NOD-Aec1Aec2 mouse model has been extensively studied to define the underlying cellular and molecular bioprocesses critical in the onset of primary Sjögren's Syndrome (pSS), a human systemic autoimmune disease characterized clinically as the loss of lacrimal and salivary gland functions leading to dry eye and dry mouth pathologies. This mouse model, together with several gene knockout mouse models of SS, has indicated that B lymphocytes, especially marginal zone B (MZB) cells, are necessary for development and onset of clinical manifestations despite the fact that destruction of the lacrimal and salivary gland cells involves a classical T cell-mediated autoimmune response. Because migrations and functions of MZB cells are difficult to study in vivo, we have carried out ex vivo investigations that use temporal global RNA transcriptomic analyses to profile autoimmunity as it develops within the salivary glands of C57BL/6.NOD-Aec1Aec2 mice. Temporal profiles indicate the appearance of Notch2-positive cells within the salivary glands of these SS-susceptible mice concomitant with the early-phase appearance of lymphocytic foci (LF). Data presented here identify cellular bioprocesses occurring during early immune cell migrations into the salivary glands and suggest MZB cells are recruited to the exocrine glands by the upregulated Cxcl13 chemokine where they recognize complement (C')-decorated antigens via their sphingosine-1-phosphate (S1P) and B cell (BC) receptors. Based on known MZB cell behavior and mobility, we propose that MZB cells activated in the salivary glands migrate to splenic follicular zones to present antigens to follicular macrophages and dendritic cells that, in turn, promote a subsequent systemic cell-mediated and autoantibody-mediated autoimmune T cell response that targets exocrine gland cells and functions. Overall, this study uses the power of transcriptomic analyses to provide greater insight into several molecular events defining cellular bioprocesses underlying SS that can be modelled and more thoroughly studied at the cellular level.

Sjogren's Syndrome and TAM Receptors: A Possible Contribution to Disease Onset.

Sjogren's syndrome (SS) is a chronic, progressive autoimmune disease featuring both organ-specific and systemic manifestations, the most frequent being dry mouth and dry eyes resulting from lymphocytic infiltration into the salivary and lacrimal glands. Like the related autoimmune disease systemic lupus erythematosus (SLE), SS patients and mouse models display accumulation of apoptotic cells and a Type I interferon (IFN) signature. Receptor tyrosine kinases (RTKs) of the Tyro3, Axl, and Mer (TAM) family are present on the surface of macrophages and dendritic cells and participate in phagocytosis of apoptotic cells (efferocytosis) and inhibition of Type I IFN signaling. This review examines the relationship between TAM receptor dysfunction and SS and explores the potential contributions of TAM defects on macrophages to SS development.

What can Sjögren's syndrome-like disease in mice contribute to human Sjögren's syndrome?

For decades, Sjögren's syndrome (SS) and Sjögren's syndrome-like (SS-like) disease in patients and mouse models, respectively, have been intensely investigated in attempts to identify the underlying etiologies, the pathophysiological changes defining disease phenotypes, the nature of the autoimmune responses, and the propensity for developing B cell lymphomas. An emerging question is whether the generation of a multitude of mouse models and the data obtained from their studies is actually important to the understanding of the human disease and potential interventional therapies. In this brief report, we comment on how and why mouse models can stimulate interest in specific lines of research that apparently parallel aspects of human SS. Focusing on two mouse models, NOD and B6·Il14α, we present the possible relevance of mouse models to human SS, highlighting a few selected disease-associated biological processes that have baffled both SS and SS-like investigations for decades.

Multiple Roles for B-Lymphocytes in Sjogren's Syndrome.

Sjogren's syndrome (SS) is a complex heterogeneous autoimmune disease resulting in loss of salivary gland and lacrimal gland function that may include multiple systemic manifestations including lymphoma. Multiple cell types participate in disease pathogenesis. This review discusses evidence for abnormal B cell subpopulations in patients with SS, critical roles of B cells in SS and the status of B cell-directed therapies in the management of patients with SS.

Oxalate-degrading microorganisms or oxalate-degrading enzymes: which is the future therapy for enzymatic dissolution of calcium-oxalate uroliths in recurrent stone disease?

Renal urolithiasis is a pathological condition common to a multitude of genetic, physiological and nutritional disorders, ranging from general hyperoxaluria to obesity. The concept of quickly dissolving renal uroliths via chemolysis, especially calcium-oxalate kidney stones, has long been a clinical goal, but yet to be achieved. Over the past 25 years, there has been a serious effort to examine the prospects of using plant and microbial oxalate-degrading enzymes known to catabolize oxalic acid and oxalate salts. While evidence is emerging that bacterial probiotics can reduce recurrent calcium-oxalate kidney stone disease by lowering systemic hyperoxaluria, the possible use of free oxalate-degrading enzyme therapy remains a challenge with several hurdles to overcome before reaching clinical practice.

Involvement of renin-angiotensin-aldosterone system in calcium oxalate crystal induced activation of NADPH oxidase and renal cell injury.

INTRODUCTION AND OBJECTIVES: Reactive oxygen species (ROS) are produced during the interaction between oxalate/calcium oxalate monohydrate (COM) crystals and renal epithelial cells and are responsible for the various cellular responses through the activation of NADPH oxidase (Nox). Ox and COM also activate the renin-angiotensin-aldosterone system (RAAS). Aldosterone stimulates ROS production through activation of Nox with the involvement of mineralocorticoid receptor (MR), Rac1 and mitogen-activated protein kinases (MAPK). We investigated RAAS pathways in vivo in an animal model of hyperoxaluria and in vitro by exposing renal epithelial cells to COM crystals. METHODS: Hyperoxaluria was induced in male SD rats by administering ethylene glycol. One group of rats was additionally given spironolactone. Total RNA was extracted and subjected to genomic microarrays to obtain global transcriptome data. Normal rat kidney cell line (NRK-52E) was incubated with aldosterone(10(-7) M) and COM(67 µg/cm(2)) with or without spironolactone(10(-5) M), a selective inhibitor of SRC family of kinases; protein phosphatase 2(pp2) (10(-5) M) and Nox inhibitor; diphenylene iodonium (DPI) (10(-5) M). RESULTS: Relative expression of genes encoding for AGT, angiotensin receptors 1b and 2, Renin 1, Cyp11b, HSD11B2, Nr3c2, NOx4 and Rac1 was upregulated in the kidneys of rats with hyperoxaluria. Treatment with spironolactone reversed the effect of hyperoxaluria. Both aldosterone and COM crystals activated Nox and Rac1 expression in NRK52E, while spironolactone inhibited Nox and Rac1 expression. Increased Rac1 expression was significantly attenuated by treatment with PP2 and spironolactone. CONCLUSIONS: Results indicate that hyperoxaluria-induced production of ROS, injury and inflammation are in part associated with the activation of Nox through renin-angiotensin-aldosterone pathway.

Csf2 and Ptgs2 Epigenetic Dysregulation in Diabetes-prone Bicongenic B6.NODC11bxC1tb Mice.

In Type 1 diabetic (T1D) human monocytes, STAT5 aberrantly binds to epigenetic regulatory sites of two proinflammatory genes, CSF2 (encoding granulocyte-macrophage colony-stimulating factor) and PTGS2 (encoding prostaglandin synthase 2/cyclooxygenase 2). Bicongenic B6.NOD C11bxC1tb mice re-create this phenotype of T1D monocytes with only two nonobese diabetic (NOD) Idd subloci (130.8 Mb-149.7 Mb, of Idd5 on Chr 1 and 32.08-53.85 Mb of Idd4.3 on Chr11) on C57BL/6 genetic background. These two Idd loci interact through STAT5 binding at upstream regulatory regions affecting Csf2 (Chr 11) and Ptgs2 (Chr 1) expression. B6.NODC11bxC1tb mice exhibited hyperglycemia and immune destruction of pancreatic islets between 8 and 30 weeks of age, with 12%-22% penetrance. Thus, B6.NODC11bxC1tb mice embody NOD epigenetic dysregulation of gene expression in myeloid cells, and this defect appears to be sufficient to impart genetic susceptibility to diabetes in an otherwise genetically nonautoimmune mouse.

Activation of the NLRP3 inflammasome in association with calcium oxalate crystal induced reactive oxygen species in kidneys.

PURPOSE: We investigated the association of hyperoxaluria and calcium oxalate crystal induced production of reactive oxygen species with activation of the NLRP3 inflammasome. MATERIALS AND METHODS: Eight-week-old male rats were given hydroxy-L-proline to induce hyperoxaluria. A group of rats on the hydroxy-L-proline diet also received apocynin, an antioxidant and nonspecific inhibitor of NADPH oxidase. At 28 days the rats were sacrificed and the kidneys were extracted. Microarray analysis was done with the BeadArray™ Reader. Gene ontology and gene pathway analyses were done with the DAVID (Database for Annotation, Visualization of Integrated Discovery) enrichment analysis tool. Quantitative real-time polymerase chain reaction and immunohistochemical staining were performed to confirm microarray results. RESULTS: Analysis of 22,226 genes revealed that 20 and 24 pathways were highly significant in the cortex and medulla, respectively. In the cortex extracellular matrix-receptor interaction, complement and coagulation cascades, focal adhesion and hypertrophic cardiomyopathy were the most significant pathways. In the medulla complement and coagulation cascades, extracellular matrix-receptor interaction and dilated cardiomyopathy were the major pathways. Genes encoding for PYCARD (ASC), TXNIP, NLRP3, caspase-1, and IL-1ß and 18 were significantly up-regulated in hydroxy-L-proline fed rats but in the group that received apocynin these genes were down-regulated in the cortex and medulla. Results were verified by quantitative real-time polymerase chain reaction with SYBR® Green assay and immunohistochemical staining. CONCLUSIONS: Results indicate a role for reactive oxygen species in activation of the NLRP3 inflammasome via TXNIP. This led to a robust inflammatory response in the kidneys of rats with hyperoxaluria and calcium oxalate nephrolithiasis.

Regulation of macromolecular modulators of urinary stone formation by reactive oxygen species: transcriptional study in an animal model of hyperoxaluria.

We used an unbiased approach of gene expression profiling to determine differential gene expression of all the macromolecular modulators (MMs) considered to be involved in stone formation, in hyperoxaluric rats, with and without treatment with the NADPH oxidase inhibitor apocynin. Male rats were fed rat chow or chow supplemented with 5% wt/wt hydroxy-l-proline (HLP) with or without apocynin-supplemented water. After 28 days, rats were euthanized and their kidneys explanted. Total RNA was isolated and microarray analysis was conducted using the Illumina bead array reader. Gene ontology analysis and the pathway analyses of the genes were done using Database for Annotation, Visualization of Integrated Discovery enrichment analysis tool. Quantitative RT-PCR of selected genes was carried out to verify the microarray results. Expression of selected gene products was confirmed using immunohistochemistry. Administration of HLP led to crystal deposition. Genes encoding for fibronectin, CD 44, fetuin B, osteopontin, and matrix-gla protein were upregulated while those encoding for heavy chains of inter-alpha-inhibitor 1, 3, and 4, calgranulin B, prothrombin, and Tamm-Horsfall protein were downregulated. HLP-fed rats receiving apocynin had a significant reversal in gene expression profiles: those that were upregulated came down while those that were downregulated stepped up. Apocynin treatment resulted in near complete absence of crystals. Clearly, there are two types of MMs; one is downregulated while the other is upregulated during hyperoxaluria and crystal deposition. Apparently gene and protein expressions of known macromolecular modulators of CaOx crystallization are likely regulated by ROS produced in part through the activation of NADPH oxidase.

Transcriptional landscapes of emerging autoimmunity: transient aberrations in the targeted tissue's extracellular milieu precede immune responses in Sjögren's syndrome.

INTRODUCTION: Our understanding of autoimmunity is skewed considerably towards the late stages of overt disease and chronic inflammation. Defining the targeted organ's role during emergence of autoimmune diseases is, however, critical in order to define their etiology, early and covert disease phases and delineate their molecular basis. METHODS: Using Sjögren's syndrome (SS) as an exemplary rheumatic autoimmune disease and temporal global gene-expression profiling, we systematically mapped the transcriptional landscapes and chronological interrelationships between biological themes involving the salivary glands' extracellular milieu. The time period studied spans from pre- to subclinical and ultimately to onset of overt disease in a well-defined model of spontaneous SS, the C57BL/6.NOD-Aec1Aec2 strain. In order to answer this aim of great generality, we developed a novel bioinformatics-based approach, which integrates comprehensive data analysis and visualization within interactive networks. The latter are computed by projecting the datasets as a whole on a priori-defined consensus-based knowledge. RESULTS: Applying these methodologies revealed extensive susceptibility loci-dependent aberrations in salivary gland homeostasis and integrity preceding onset of overt disease by a considerable amount of time. These alterations coincided with innate immune responses depending predominantly on genes located outside of the SS-predisposing loci Aec1 and Aec2. Following a period of transcriptional stability, networks mapping the onset of overt SS displayed, in addition to natural killer, T- and B-cell-specific gene patterns, significant reversals of focal adhesion, cell-cell junctions and neurotransmitter receptor-associated alterations that had prior characterized progression from pre- to subclinical disease. CONCLUSIONS: This data-driven methodology advances unbiased assessment of global datasets an allowed comprehensive interpretation of complex alterations in biological states. Its application delineated a major involvement of the targeted organ during the emergence of experimental SS.

The Interferon-Signature of Sjögren's Syndrome: How Unique Biomarkers Can Identify Underlying Inflammatory and Immunopathological Mechanisms of Specific Diseases.

Innate immune responses direct the nature and specificity of downstream adaptive responses in autoimmune diseases. One of the strongest markers of innate immunity is the up-regulated expression of interferon (IFN) and IFN-responsive/stimulated genes (IRGs/ISGs). While multiple IRGs are induced during the innate phase of host responses, transcriptome data suggest unique IRG-signatures for different diseases. Sjögren's syndrome (SjS) is characterized by chronic immune attacks against exocrine glands leading to exocrine dysfunction, plus strong up-regulated expressions of IFN IRG transcripts. Genome-wide transcriptome analyses indicate that differentially expressed IRGs are restricted during disease development and therefore define underlying etiopathological mechanisms. Here we review the innate immune-associated IFN-signature of SjS and show how differential gene expressions of IRG/ISG sets interact molecularly and biologically to identify critical details of SjS etiopathogenesis.

NADPH oxidase as a therapeutic target for oxalate induced injury in kidneys.

A major role of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family of enzymes is to catalyze the production of superoxides and other reactive oxygen species (ROS). These ROS, in turn, play a key role as messengers in cell signal transduction and cell cycling, but when they are produced in excess they can lead to oxidative stress (OS). Oxidative stress in the kidneys is now considered a major cause of renal injury and inflammation, giving rise to a variety of pathological disorders. In this review, we discuss the putative role of oxalate in producing oxidative stress via the production of reactive oxygen species by isoforms of NADPH oxidases expressed in different cellular locations of the kidneys. Most renal cells produce ROS, and recent data indicate a direct correlation between upregulated gene expressions of NADPH oxidase, ROS, and inflammation. Renal tissue expression of multiple NADPH oxidase isoforms most likely will impact the future use of different antioxidants and NADPH oxidase inhibitors to minimize OS and renal tissue injury in hyperoxaluria-induced kidney stone disease.

Rapid oxalate determination in blood and synthetic urine using a newly developed oxometer.

Blood and urine oxalate determinations have been limited to the laboratory setting because of complex sample storage and processing methods as well as the need for color spectrophotometry and ion chromatography. We hypothesized that glucometer test strips, impregnated with glucose oxidase and dyes that measure secondary hydrogen peroxide production, could be infused with oxalate oxidase and produce enhanced color changes in the presence of oxalate. By increasing the amount of sodium oxalate in fresh blood, we found that glucometer-measured oxalate increased on a linear scale. In addition, oxalate levels in synthetic urine could be measured using a visual scale, suggesting that strip dwell time or oxalate/oxalate oxidase concentrations could be manipulated to enhance optimal sensitivity. Although further testing is necessary, this simple, first-generation oxometer may eventually allow point of care testing in the home or office, empowering patients with oxalate-based medical conditions and giving healthcare providers real-time oxalate feedback.

Systems analysis of primary Sjögren's syndrome pathogenesis in salivary glands identifies shared pathways in human and a mouse model.

INTRODUCTION: Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease with complex etiopathogenesis. Despite extensive studies to understand the disease process utilizing human and mouse models, the intersection between these species remains elusive. To address this gap, we utilized a novel systems biology approach to identify disease-related gene modules and signaling pathways that overlap between humans and mice. METHODS: Parotid gland tissues were harvested from 24 pSS and 16 non-pSS sicca patients and 25 controls. For mouse studies, salivary glands were harvested from C57BL/6.NOD-Aec1Aec2 mice at various times during development of pSS-like disease. RNA was analyzed with Affymetrix HG U133+2.0 arrays for human samples and with MOE430+2.0 arrays for mouse samples. The images were processed with Affymetrix software. Weighted-gene co-expression network analysis was used to identify disease-related and functional pathways. RESULTS: Nineteen co-expression modules were identified in human parotid tissue, of which four were significantly upregulated and three were downregulated in pSS patients compared with non-pSS sicca patients and controls. Notably, one of the human disease-related modules was highly preserved in the mouse model, and was enriched with genes involved in immune and inflammatory responses. Further comparison between these two species led to the identification of genes associated with leukocyte recruitment and germinal center formation. CONCLUSION: Our systems biology analysis of genome-wide expression data from salivary gland tissue of pSS patients and from a pSS mouse model identified common dysregulated biological pathways and molecular targets underlying critical molecular alterations in pSS pathogenesis.

Apocynin-treatment reverses hyperoxaluria induced changes in NADPH oxidase system expression in rat kidneys: a transcriptional study.

PURPOSE: We have previously shown that production of reactive oxygen species (ROS) is an important contributor to renal injury and inflammation following exposure to oxalate (Ox) or calcium-oxalate (CaOx) crystals. The present study was conducted, utilizing global transcriptome analyses, to determine the effect of Apocynin on changes in the NADPH oxidase system activated in kidneys of rats fed a diet leading to hyperoxaluria and CaOx crystal deposition. APPROACH: Age-, sex- and weight-matched rats were either fed regular rat chow or regular rat chow supplemented with 5% w/w hydroxy-L-proline (HLP). Half of the rats on the HLP diet were also placed on Apocynin-supplemented H(2)O. After 28 days, each rat was euthanized, their kidneys freshly explanted and dissected to obtain both cortex and medulla tissues. Total RNA was extracted from each tissue and subjected to genomic microarrays to obtain global transcriptome data. KEGG was used to identify gene clusters with differentially expressed genes. Immunohistochemistry was used to confirm protein expressions of selected genes. RESULTS: Genes encoding both membrane- and cytosolic-NADPH oxidase complex-associated proteins, together with p21rac and Rap1a, were coordinately up-regulated significantly in both renal medulla and cortex tissues in the HLP-fed rats compared to normal healthy untreated controls. Activation of NADPH oxidase appears to occur via the angiotensin-II/angiotensin-II receptor-2 pathway, although the DAG-PKC pathway of neutrophils may also contribute. Immuno histochemical staining confirmed up-regulated gene expressions. Simultaneously, genes encoding ROS scavenger proteins were down-regulated. HLP-fed rats receiving Apocynin had a complete reversal in the differential-expression of the NADPH oxidase system genes, despite showing similar levels of hyperoxaluria. CONCLUSIONS: A strong up-regulation of an oxidative/respiratory burst involving the NADPH oxidase system, activated via the angiotensin-II and most likely the DAG-PKC pathways, occurs in kidneys of hyperoxaluric rats. Apocynin treatment reversed this activation without affecting the levels of hyperoxaluria.