Short-chain fatty acid mitigates adenine-induced chronic kidney disease via FFA2 and FFA3 pathways.

Short-chain fatty acids (SCFAs), including acetate, butyrate, and propionate, are produced when colonic bacteria in the human gastrointestinal tract ferment undigested fibers. Free fatty acid receptor 2 (FFA2) and FFA3 are G-protein-coupled receptors recently identified as SCFA receptors that may modulate inflammation. We previously showed through in vitro experiments that SCFAs activate FFA2 and FFA3, thereby mitigating inflammation in human renal cortical epithelial cells. This study used a murine model of adenine-induced renal failure to investigate whether or not SCFAs can prevent the progression of renal damage. We also examined whether or not these FFA2 and FFA3 proteins have some roles in this protective mechanism in vivo. Immunohistochemical analyses of mouse kidneys showed that FFA2 and FFA3 proteins were expressed mainly in the distal renal tubules and collecting tubules. First, we observed that the administration of propionate mitigated the renal dysfunction and pathological deterioration caused by adenine. Consistent with this, the expression of inflammatory cytokines and fibrosis-related genes was reduced. Furthermore, the mitigation of adenine-induced renal damage by the administration of propionate was significantly attenuated in FFA2-/- and FFA3-/- mice. Therefore, the administration of propionate significantly protects against adenine-induced renal failure, at least in part, via the FFA2 and FFA3 pathways. Our data suggest that FFA2 and FFA3 are potential new therapeutic targets for preventing or delaying the progression of chronic kidney disease.

Comparison of the renal cortex and the medulla for antibody mediated rejection.

OBJECTIVES: The presence of the peritubular capillaritis and its extent are important for diagnosis of the antibody-mediated rejection in kidneys. However, it is recommended that peritubular capillaritis should only be scored in the cortex. This study aims to focus on peritubular capillaritis scoring both in the cortex and the medulla to understand the value of the medulla in the diagnosis of antibody-mediated rejection. METHODS: Fifty-one allograft renal biopsy were re-evaluated for peritubular capillaritis, C4d and acute tubular injury, separately for the cortex and the medulla according to the Banff. RESULTS: Seventeen cases (33.3%) had peritubular capillaritis both in the cortex and the medulla and three (5.9%) cases had peritubular capillaritis only in the cortex while five (9.8%) cases had only in the medulla. Eighteen (35%) of the cases had C4d staining both in the cortex and the medulla and 14 (27.5%) cases had C4d positivity only in the cortex and 18 (35.3%) cases only in the medulla. Twenty-three (45%) cases had acute tubular injury both in the cortex and the medulla and 31 (60.7%) cases had acute tubular injury only in the cortex and 23 (45.1%) cases had only in the medulla. The sensitivity, specificity, positive and negative predictive values of medullar peritubular capillaritis predicting cortical peritubular capillaritis were 85.7%, 86.7%, 81.8% and 89.7%, respectively. CONCLUSION: In case of absence of the cortical tissue, medulla can be used as a reference for antibody-mediated rejection considering the morphological features, results of donor-specific antibody and renal function tests.

The transcription factor Twist1 in the distal nephron but not in macrophages propagates aristolochic acid nephropathy.

Tubulointerstitial disease in the kidney culminates in renal fibrosis that portents organ failure. Twist1, a basic helix-loop-helix protein 38 transcription factor, regulates several essential biological functions, but inappropriate Twist1 activity in the kidney epithelium can trigger kidney fibrogenesis and chronic kidney disease. By contrast, Twist1 in circulating myeloid cells may constrain inflammatory injury by attenuating cytokine generation. To dissect the effects of Twist1 in kidney tubular versus immune cells on renal inflammation following toxin-induced renal injury, we subjected mice with selective deletion of Twist1 in renal epithelial cells or macrophages to aristolochic acid-induced chronic kidney disease. Ablation of Twist1 in the distal nephron attenuated kidney damage, interstitial fibrosis, and renal inflammation after aristolochic acid exposure. However, macrophage-specific deletion of Twist1 did not impact the development of aristolochic acid-induced nephropathy. In vitro studies confirmed that Twist1 in renal tubular cells underpins their susceptibility to apoptosis and propensity to generate pro-fibrotic mediators in response to aristolochic acid. Moreover, co-culture studies revealed that Twist1 in renal epithelia augmented the recruitment and activation of pro-inflammatory CD64+ macrophages. Thus, Twist1 in the distal nephron rather than in infiltrating macrophages propagates chronic inflammation and fibrogenesis during aristolochic acid-induced nephropathy.

Distal renal tubular acidosis in Sjögren's syndrome.

Interstitial nephritis and immune complex-mediated glomerulonephritis are the two common renal manifestations of primary Sjögren's syndrome (SS). Here, we discuss three cases of primary SS where presenting manifestation was distal renal tubular acidosis. The possibility of an underlying autoimmune disorder should be considered in a patient presenting with distal tubular acidosis or recurrent hypokalemic periodic paralysis as treatment of primary disease improves the outcome of illness.

CD8+ T cells stimulate Na-Cl co-transporter NCC in distal convoluted tubules leading to salt-sensitive hypertension.

Recent studies suggest a role for T lymphocytes in hypertension. However, whether T cells contribute to renal sodium retention and salt-sensitive hypertension is unknown. Here we demonstrate that T cells infiltrate into the kidney of salt-sensitive hypertensive animals. In particular, CD8+ T cells directly contact the distal convoluted tubule (DCT) in the kidneys of DOCA-salt mice and CD8+ T cell-injected mice, leading to up-regulation of the Na-Cl co-transporter NCC, p-NCC and the development of salt-sensitive hypertension. Co-culture with CD8+ T cells upregulates NCC in mouse DCT cells via ROS-induced activation of Src kinase, up-regulation of the K+ channel Kir4.1, and stimulation of the Cl- channel ClC-K. The last event increases chloride efflux, leading to compensatory chloride influx via NCC activation at the cost of increasing sodium retention. Collectively, these findings provide a mechanism for adaptive immunity involvement in the kidney defect in sodium handling and the pathogenesis of salt-sensitive hypertension.

Activation of endogenous anti-inflammatory mediator cyclic AMP attenuates acute pyelonephritis in mice induced by uropathogenic Escherichia coli.

The pathogenesis of pyelonephritis caused by uropathogenic Escherichia coli (UPEC) is not well understood. Here, we show that besides UPEC virulence, the severity of the host innate immune response and invasion of renal epithelial cells are important pathogenic factors. Activation of endogenous anti-inflammatory mediator cAMP significantly attenuated acute pyelonephritis in mice induced by UPEC. Administration of forskolin (a potent elevator of intracellular cAMP) reduced kidney infection (ie, bacterial load, tissue destruction); this was associated with attenuated local inflammation, as evidenced by the reduction of renal production of proinflammatory mediators, renal infiltration of inflammatory cells, and renal myeloperoxidase activity. In primary cell culture systems, forskolin not only down-regulated UPEC-stimulated production of proinflammatory mediators by renal tubular epithelial cells and inflammatory cells (eg, monocyte/macrophages) but also reduced bacterial internalization by renal tubular epithelial cells. Our findings clearly indicate that activation of endogenous anti-inflammatory mediator cAMP is beneficial for controlling UPEC-mediated acute pyelonephritis in mice. The beneficial effect can be explained at least in part by limiting excessive inflammatory responses through acting on both renal tubular epithelial cells and inflammatory cells and by inhibiting bacteria invasion of renal tubular epithelial cells.

Distal renal tubules are deficient in aggresome formation and autophagy upon aldosterone administration.

Prolonged elevations of plasma aldosterone levels are associated with renal pathogenesis. We hypothesized that renal distress could be imposed by an augmented aldosterone-induced protein turnover challenging cellular protein degradation systems of the renal tubular cells. Cellular accumulation of specific protein aggregates in rat kidneys was assessed after 7 days of aldosterone administration. Aldosterone induced intracellular accumulation of 60 s ribosomal protein L22 in protein aggregates, specifically in the distal convoluted tubules. The mineralocorticoid receptor inhibitor spironolactone abolished aldosterone-induced accumulation of these aggregates. The aldosterone-induced protein aggregates also contained proteasome 20 s subunits. The partial de-ubiquitinase ataxin-3 was not localized to the distal renal tubule protein aggregates, and the aggregates only modestly colocalized with aggresome transfer proteins dynactin p62 and histone deacetylase 6. Intracellular protein aggregation in distal renal tubules did not lead to development of classical juxta-nuclear aggresomes or to autophagosome formation. Finally, aldosterone treatment induced foci in renal cortex of epithelial vimentin expression and a loss of E-cadherin expression, as signs of cellular stress. The cellular changes occurred within high, but physiological aldosterone concentrations. We conclude that aldosterone induces protein accumulation in distal renal tubules; these aggregates are not cleared by autophagy that may lead to early renal tubular damage.

Everything you need to know about distal renal tubular acidosis in autoimmune disease.

Renal acid-base homeostasis is a complex process, effectuated by bicarbonate reabsorption and acid secretion. Impairment of urinary acidification is called renal tubular acidosis (RTA). Distal renal tubular acidosis (dRTA) is the most common form of the RTA syndromes. Multiple pathophysiologic mechanisms, each associated with various etiologies, can lead to dRTA. The most important consequence of dRTA is (recurrent) nephrolithiasis. The diagnosis is based on a urinary acidification test. Potassium citrate is the treatment of choice.

Diffuse proliferative glomerulonephritis associated with dermatomyositis with nephrotic syndrome.

We described a 44-year-old man developing dermatomyositis (DM) and nephrotic syndrome (NS). Renal biopsy revealed diffuse proliferative glomerulonephritis (DPGN) with depositions of immunoglobulin and complements. A combination therapy of steroid and cyclophosphamide (CTX) was found very effective for the patient. Chronic glomerulonephritis is rare in DM. In our review of related literature, membranous glomerulonephritis (MN) is the main type of glomerular lesion, another type is mesangial proliferative glomerulonephritis (mesPGN). Here we reported a case of DM associated with DPGN developing NS, which was not found in existing literature. Although glomerulonephritis is uncommon in patients with DM, renal pathology is not as simplex as previously thought, and treatment with steroid or/and cytotoxic drugs is favorable for prognosis.

Active synthesis of mouse polymeric immunoglobulin receptor in the epithelial cells of the distal urinary tubule in kidney.

The tissue distribution of mouse polymeric immunoglobulin receptor (pIgR) has been demonstrated. By Northern blot hybridization, pIgR mRNA expression was detected in liver, intestine, stomach, lung and kidney. A weak expression was also detected in thymus by reverse transcriptase-polymerase chain reaction. The pIgR expression in kidney was further studied and confirmed that pIgR protein was actively synthesized in the epithelial cells of distal urinary tubule and of Henle's loop. Immunoelectron microscopical analysis showed the accumulation of pIgR-containing vesicles in the apical portion of distal urinary tubule epithelial cells.

Predominance of Th1 immune response in diffuse proliferative lupus nephritis.

OBJECTIVE: Lupus nephritis, which shows various histologic patterns, is a serious complication of systemic lupus erythematosus (SLE). We previously demonstrated the importance of Thl cell-mediated immune response in patients with diffuse proliferative lupus nephritis (DPLN). The aim of this study was to examine the relationship between the peripheral blood Th1/Th2 balance and the intrarenal immune response. METHODS: The Th1:Th2 ratio in peripheral blood was measured by intracellular staining for cytokines with flow cytometry. Immunohistochemical analysis of renal biopsy specimens was performed to clarify the characterization of local infiltrating cells in 3 groups of subjects: SLE patients with World Health Organization (WHO) class IV nephritis (DPLN) (group I; n = 13), SLE patients with WHO class V nephritis (group II; n = 9), and patients with minor glomerular lesions (group III; n = 7). In addition, the histologic activity index and chronicity index were evaluated and correlated with the Th1:Th2 ratio. RESULTS: Immunohistochemical studies showed higher numbers of CD68+ macrophages, CD3 + T cells, and interferon-gamma-positive cells in group I than in groups II or III. Renal tissues from patients in group I also showed up-regulation of expression of osteopontin and CD40, with a small number of infiltrating T cells expressing interleukin-4. Overall, the Thl:Th2 ratio in group I patients (SLE with DPLN) was high and correlated significantly with the histologic activity index, but not with the chronicity index. CONCLUSION: We have identified a predominance of Thl-type response in both peripheral and renal tissues of patients with DPLN, suggesting that the peripheral blood Thl:Th2 ratio directly reflects the local histopathologic findings. In patients with lupus nephritis, the peripheral blood Th1:Th2 ratio could be useful as a parameter that reflects the renal histologic activity or the strength of the local Thl response.

Tubulointerstitial nephritis antigen (TIN-ag) is expressed in distinct segments of the developing human nephron.

Tubulointerstitial nephritis antigen (TIN-ag) is a 58 kDa glycoprotein restricted within the kidney to basement membranes underlying the epithelium of Bowman's capsule and proximal and distal tubules. Autoantibody formation against this component has been described in association with primary immune-mediated tubulointerstital nephritis, membranous nephropathy and anti-glomerular basement membrane nephritis. In the present report, the ontogeny of this protein was studied in human fetal kidney tissue by immunohistochemical analysis of immature and developing nephrons using a panel of monoclonal and polyclonal antibodies. TIN-ag is first detected in basement membranes underlying the epithelium of Bowman's capsule of early capillary loop stage glomeruli and the primitive proximal tubule. No detectable expression is observed in the basement membranes of the branching ureteric bud, nephrogenic vesicle, or comma shape and s-shape stages of nephrogenic development. Increased staining of the proximal tubular basement membrane is associated with outgrowth of the primitive tubule from the urinary pole of the developing glomerulus. In more mature fetal tubules, TIN-ag expression closely resembles that of previously reported observations in mature tissue where it is present in high amounts in the basement membranes of proximal tubules, and to a lesser extent in Bowman's capsule and distal tubules. Our results suggest that TIN-ag expression is developmentally regulated in a precise spatial and temporal pattern throughout nephrogenesis.

Relationship between expression of epidermal growth factor and simian virus 40 T antigen in a line of transgenic mice.

The pattern of expression of the simian virus 40 (SV40) T antigen gene and resultant dysplasia were re-examined in a line of transgenic mice in which the T antigen gene was under the control of the SV40 early promoter. We found that T antigen expression in the kidney, and resulting dysplastic lesions, occurred exclusively in the distal convoluted tubules and the ascending limbs of Henle. Epidermal growth factor (EGF) expression in the kidney of normal mice was similarly immunolocalized. The correlation between high EGF immunoreactivity in normal mouse tissues and T antigen expression in the transgenic counterpart was also seen in the choroid plexus epithelium and in the submandibular glands of male mice. T antigen was not found in the submandibular gland of transgenic females. Similarly, EGF was only rarely detected in the normal female submandibular gland. In contrast to the correlation between T antigen expression in the transgenic mice and EGF expression in the corresponding tissues of the normal mice, within the dysplastic lesions of the transgenic mice EGF expression was severely diminished. Adenocarcinomas of the male submandibular gland from another line of transgenic mice that expresses the Int-1 transgene, showed similarly reduced levels of immunostaining for EGF. Thus, reduced expression of EGF might be a general feature of dysplasia and tumorigenesis in those tissues that normally express EGF.

Heterogeneity of renal carcinoma.

Monoclonal antibodies were used to study the expression of three recently characterized basement membrane components and two carbohydrate antigens in 11 renal-cell carcinomas, using immunohistological and biochemical techniques. The expression of several site-specific kidney antigens in renal-cell carcinoma were studied to determine the origin of the carcinoma and if it is possible further classify this type of carcinoma. Tubulointerstitial nephritis antigen (TIN) and two alpha-chains of type IV collagen, alpha 1 (IV) and alpha 3 (IV) were studied. In addition the expression of carbohydrate antigens Lex and SLex, which also exhibit site-specific distribution were characterized. Lex and SLex antibodies stained the majority of the tumours. TIN was expressed in 9 of 11 tumours, the alpha 1 (IV) chain was present in all 11, and the alpha 3 (IV) chain in two of the 11 tumours. Interestingly, the two alpha 3 (IV)-positive tumours were the same two that were negative for TIN. In normal tissue alpha 3 (IV) is found in distal tubules while TIN is found in proximal tubules. Our results are consistent with earlier observations that the proximal tubule is the origin of most renal-cell carcinomas, but the results also indicate that renal-cell carcinoma may originate from the distal tubule.

Laminin, fibronectin, and Goodpasture antigen detection in patients with Alport's syndrome.

Indirect immunofluorescence study with laminin and fibronectin monoclonal antibodies on paraffin sections, as well as with serum from a patient with Goodpasture's syndrome with high titer of autoantibodies that recognize the antigenic determinants in human glomerular and tubular basement membrane, was performed on 14 patients with Alport's syndrome and 5 specimens of normal renal tissue obtained from donors in cases of renal transplantation (control group). We found no binding of Goodpasture antigen to glomerular and distal tubular basement membranes in renal biopsy tissue from all 14 patients with Alport's syndrome. In contrast, there was bright linear fluorescence of Goodpasture antigen on glomerular and tubular basement membranes of normal renal material. There was no difference in laminin and fibronectin binding in patients with Alport's syndrome and controls. In all the cases binding was strongly positive. These results suggest an abnormality or absence of immunoreactive autoantigen in the glomerular and distal tubular basement membrane in patients with Alport's syndrome. Therefore, Goodpasture antigen detection could be an important diagnostic method in early stages of Alport's syndrome when characteristic morphological changes are not yet developed.

Immunological segmentation of the rabbit distal, connecting, and collecting tubules.

To obtain monoclonal antibodies (MAB) specific for the different cell types of distal and collecting tubules, BALB/c mice were immunized with cell suspensions highly enriched in cells from the distal segments of the rabbit nephron. Nine MAB were selected and cloned. Four groups could be identified on the basis of double-labeling immunofluorescence (IF) on frozen kidney sections and on microdissected tubules. In addition, binding specificity at the cellular level was studied by immunoelectronmicroscopy (IEM) for selected MAB. A single MAB (group 1) was specific for distal bright cells and a subpopulation of cortical ascending limb cells. Six MAB (group 2) reacted with connecting and collecting tubules. Five of these (group 2A) had similar binding patterns and reacted identically with the two tubular segments. The MAB studied by IEM was specific for connecting and principal cells. One antibody (group 2B) reacted with only a fraction of the cells associated with the connecting tubule (CNT), but with all cells of the cortical collecting tubule (CCT). By IEM, this antibody was found to be specific for intercalated cells in CNT and bound both principal and intercalated cells of the CCT. Two MAB (group 3) reacted with antigen(s) expressed by the various terminal segments of renal tubule. MAB of groups 1 and 2A, which define distal bright cells and connecting-principal cells from the CNT-CCT, respectively, were used for cell fractionation experiments. Heterogeneous rabbit cortical cells were first incubated with the selected MAB. MAB-bearing renal cells were separated on plastic dishes previously coated with an affinity-purified goat anti-mouse immunoglobulin. Using these procedures it was possible to obtain highly purified subpopulations of distal, bright, or connecting-principal cells.

Secretory immune responses in human kidneys.

The secretory immune system has been well studied in the intestinal, bronchial, and biliary systems and breast. Tissue studies of secretory immunoglobulins in the kidney are scanty, mostly related to nephropathies with IgA. Renal tissues from 37 autopsies selected for any history of renal dysfunction were processed for immunohistologic studies on frozen sections with several antisera, including a purified rabbit anti-human secretory component (SC). By immunohistology, gel diffusion, and immunoblotting, the anti-SC antibody reacted appropriately with purified human SC, saliva, intestinal epithelium, and breast milk and did not cross-react with immunoglobulin heavy or light chains, lactoferrin, and other tissue proteins. IgA and SC were seen in tubular casts in 70% of patients, whereas less impressive staining with IgM, IgG, and albumin was seen, respectively, in 24%, 13%, and 22% of the patients. SC was present in the cytoplasm of distal tubule and Henle's loop cells in 78% of specimens. A control group of 10 healthy individuals who died suddenly showed minimal staining of casts and tubules in 2 specimens. Renal pathology in the group with IgA-SC+ casts included acute tubular necrosis (54%), severe chronic renal disease (61%), and mild chronic renal injury (38%). The group with negative IgA-SC casts included acute tubular necrosis (64%), infectious interstitial nephritis (36%), and negligible renal disease (36%). This study suggests that discrete distal segments of the nephron may have the capability of secreting SC, which is probably coupled with serum-derived IgA and incorporated into luminal tubular secretions. The low level of immunosecretions in kidneys which are normal or minimally damaged suggests that this system may need to be turned on by unknown, probably pathogenic stimulating factors.

Phagocytosis of E. coli by renal tubular epithelia.

Despite significant advances in our understanding or renal tubular cell function, the in vivo handling of E. coli by renal tubules has not been previously investigated. The present studies were, therefore, designed to study this aspect of nephron function. Live and dead E. coli and vehicle alone were microinjected into the proximal tubular lumen of a single nephron of rats, and the microinjected tubules were morphologically studied at one-half, two, four, and six hours after. The bacteria initially contacted the luminal cell membrane. The luminal cell membrane adjacent to the bacteria subsequently invaginated, and both live and dead E. coli eventually became internalized into the tubular epithelial cytoplasm. Since dead E. coli are unlikely to invade the cells, their intracytoplasmic localization is a result of tubular epithelial phagocytosis. Similar microinjections of dead E. coli together with rat erythrocytes revealed a preferential phagocytosis of dead E. coli. Examination of the microinjected nephron with dead E. coli 48 hours after also demonstrated a development of microscopic interstitial nephritis surrounding the microinjected tubule. In conclusion, the renal tubular epithelia of the proximal and distal segments of rat nephron have phagocytic potential for E. coli which are further capable of inducing an inflammatory reaction around the microinjected tubule.