Podocyte-Specific Deletion of MCP-1 Fails to Protect against Angiotensin II- or Adriamycin-Induced Glomerular Disease

Investigating the role of podocytes in proteinuric disease is imperative to address the increasing global burden of chronic kidney disease (CKD). Studies strongly implicate increased levels of monocyte chemoattractant protein-1 (MCP-1/CCL2) in proteinuric CKD. Since podocytes express the receptor for MCP-1 (i.e., CCR2), we hypothesized that podocyte-specific MCP-1 production in response to stimuli could activate its receptor in an autocrine manner, leading to further podocyte injury. To test this hypothesis, we generated podocyte-specific MCP-1 knockout mice (Podo-Mcp-1fl/fl) and exposed them to proteinuric injury induced by either angiotensin II (Ang II; 1.5 mg/kg/d, osmotic minipump) or Adriamycin (Adr; 18 mg/kg, intravenous bolus). At baseline, there were no between-group differences in body weight, histology, albuminuria, and podocyte markers. After 28 days, there were no between-group differences in survival, change in body weight, albuminuria, kidney function, glomerular injury, and tubulointerstitial fibrosis. The lack of protection in the knockout mice suggests that podocyte-specific MCP-1 production is not a major contributor to either Ang II- or Adr-induced glomerular disease, implicating that another cell type is the source of pathogenic MCP-1 production in CKD.

Persistent DNA damage underlies tubular cell polyploidization and progression to chronic kidney disease in kidneys deficient in the DNA repair protein FAN1

Defective DNA repair pathways contribute to the development of chronic kidney disease (CKD) in humans. However, the molecular mechanisms underlying DNA damage-induced CKD pathogenesis are not well understood. Here, we investigated the role of tubular cell DNA damage in the pathogenesis of CKD using mice in which the DNA repair protein Fan1 was knocked out. The phenotype of these mice is orthologous to the human DNA damage syndrome, karyomegalic interstitial nephritis (KIN). Inactivation of Fan1 in kidney proximal tubule cells sensitized the kidneys to genotoxic and obstructive injury characterized by replication stress and persistent DNA damage response activity. Accumulation of DNA damage in Fan1 tubular cells induced epithelial dedifferentiation and tubular injury. Characteristic to KIN, cells with chronic DNA damage failed to complete mitosis and underwent polyploidization. In vitro and in vivo studies showed that polyploidization was caused by the overexpression of DNA replication factors CDT1 and CDC6 in FAN1 deficient cells. Mechanistically, inhibiting DNA replication with Roscovitine reduced tubular injury, blocked the development of KIN and mitigated kidney function in these Fan1 knockout mice. Thus, our data delineate a mechanistic pathway by which persistent DNA damage in the kidney tubular cells leads to kidney injury and development of CKD. Furthermore, therapeutic modulation of cell cycle activity may provide an opportunity to mitigate the DNA damage response induced CKD progression.

Suppression of NRF2 Activity by HIF-1α Promotes Fibrosis after Ischemic Acute Kidney Injury

Acute kidney injury (AKI) is a rapid decline in renal function and can occur after ischemia/reperfusion injury (IRI) to the tubular epithelia. The nuclear factor erythroid-2-related factor 2 (NRF2) pathway protects against AKI and AKI-to-chronic kidney disease (CKD) progression, but we previously demonstrated that severe IRI maladaptively reduced NRF2 activity in mice. To understand the mechanism of this response, we subjected C57BL/6J mice to unilateral kidney IRI with ischemia times that were titrated to induce mild to severe injury. Mild IRI increased NRF2 activity and was associated with renal recovery, whereas severe IRI decreased NRF2 activity and led to progressive CKD. Due to these effects of ischemia, we tested the hypothesis that hypoxia-inducible factor-1α (HIF-1α) mediates NRF2 activity. To mimic mild and severe ischemia, we activated HIF-1α in HK-2 cells in nutrient-replete or nutrient-deficient conditions. HIF-1α activation in nutrient-replete conditions enhanced NRF2 nuclear localization and activity. However, in nutrient-deficient conditions, HIF-1α activation suppressed NRF2 nuclear localization and activity. Nuclear localization was rescued with HIF-1α siRNA knockdown. Our results suggest that severe ischemic AKI leads to HIF-1α-mediated suppression of NRF2, leading to AKI-to-CKD progression.

Genetic or pharmacologic Nrf2 activation increases proteinuria in chronic kidney disease in mice

The nuclear factor erythroid 2-related factor 2 (Nrf2) pathway upregulates key cellular defenses. Clinical trials are utilizing pharmacologic Nrf2 inducers such as bardoxolone methyl to treat chronic kidney disease, but Nrf2 activation has been linked to a paradoxical increase in proteinuria. To understand this effect, we examined genetically engineered mice with elevated Nrf2 signaling due to reduced expression of the Nrf2 inhibitor, Kelch-like ECH-associated protein 1 (Keap1). These Keap1^FA/FA mice lacked baseline proteinuria but exhibited increased proteinuria in experimental models evoked by adriamycin, angiotensin II, or protein overload. After injury, Keap1^FA/FA mice had increased glomerulosclerosis, nephrin disruption and shedding, podocyte injury, foot process effacement, and interstitial fibrosis. Keap1^FA/FA mice also had higher daytime blood pressures and lower heart rates measured by radiotelemetry. Conversely, Nrf2 knockout mice were protected from proteinuria. We also examined the pharmacologic Nrf2 inducer CDDO-Im. Compared to angiotensin II alone, the combination of angiotensin II and CDDO-Im significantly increased proteinuria, a phenomenon not observed in Nrf2 knockout mice. This effect was not accompanied by additional increases in blood pressure. Finally, Nrf2 was found to be upregulated in the glomeruli of patients with focal segmental glomerulosclerosis, diabetic nephropathy, fibrillary glomerulonephritis, and membranous nephropathy. Thus, our studies demonstrate that Nrf2 induction in mice may exacerbate proteinuria in chronic kidney disease.

Paraoxonase 3 functions as a chaperone to decrease functional expression of the epithelial sodium channel

The paraoxonase (PON) family comprises three highly conserved members: PON1, PON2, and PON3. They are orthologs of Caenorhabditis elegans MEC-6, an endoplasmic reticulum-resident chaperone that has a critical role in proper assembly and surface expression of the touch-sensing degenerin channel in nematodes. We have shown recently that MEC-6 and PON2 negatively regulate functional expression of the epithelial Na⁺ channel (ENaC), suggesting that the chaperone function is conserved within this family. We hypothesized that other PON family members also modulate ion channel expression. Pon3 is specifically expressed in the aldosterone-sensitive distal tubules in the mouse kidney. We found here that knocking down endogenous Pon3 in mouse cortical collecting duct cells enhanced Na⁺ transport, which was associated with increased γENaC abundance. We further examined Pon3 regulation of ENaC in two heterologous expression systems, Fisher rat thyroid cells and Xenopus oocytes. Pon3 coimmunoprecipitated with each of the three ENaC subunits in Fisher rat thyroid cells. As a result of this interaction, the whole-cell and surface abundance of ENaC α and γ subunits was reduced by Pon3. When expressed in oocytes, Pon3 inhibited ENaC-mediated amiloride-sensitive Na⁺ currents, in part by reducing the surface expression of ENaC. In contrast, Pon3 did not alter the response of ENaC to chymotrypsin-mediated proteolytic activation or [2-(trimethylammonium)ethyl]methanethiosulfonate-induced activation of αβ_S518Cγ, suggesting that Pon3 does not affect channel open probability. Together, our results suggest that PON3 regulates ENaC expression by inhibiting its biogenesis and/or trafficking.

Ultrasound super-resolution imaging provides a noninvasive assessment of renal microvasculature changes during mouse acute kidney injury

Acute kidney injury (AKI) is a risk factor for the development of chronic kidney disease (CKD). One mechanism for this phenomenon is renal microvascular rarefaction and subsequent chronic impairment in perfusion. However, diagnostic tools to monitor the renal microvasculature in a noninvasive and quantitative manner are still lacking. Ultrasound super-resolution imaging is an emerging technology that can identify microvessels with unprecedented resolution. Here, we applied this imaging technique to identify microvessels in the unilateral ischemia-reperfusion injury mouse model of AKI-to-CKD progression in vivo. Kidneys from 21 and 42 day post- ischemia-reperfusion injury, the contralateral uninjured kidneys, and kidneys from sham-operated mice were examined by ultrasound super-resolution and histology. Renal microvessels were successfully identified by this imaging modality with a resolution down to 32 μm. Renal fibrosis was observed in all kidneys with ischemia-reperfusion injury and was associated with a significant reduction in kidney size, cortical thickness, relative blood volume, and microvascular density as assessed by this imaging. Tortuosity of the cortical microvasculature was also significantly increased at 42 days compared to sham. These vessel density measurements correlated significantly with CD31 immunohistochemistry (R²=0.77). Thus, ultrasound super-resolution imaging provides unprecedented resolution and is capable of noninvasive quantification of renal vasculature changes associated with AKI-to-CKD progression in mice. Hence, this technique could be a promising diagnostic tool for monitoring progressive kidney disease.

Tubular injury triggers podocyte dysfunction by β-catenin-driven release of MMP-7

Proteinuric chronic kidney disease (CKD) remains a major health problem worldwide. While it is well established that the progression of primary glomerular disease induces tubulointerstitial lesions, how tubular injury triggers glomerular damage is poorly understood. We hypothesized that injured tubules secrete mediators that adversely affect glomerular health. To test this, we used conditional knockout mice with tubule-specific ablation of β-catenin (Ksp-β-cat-/-) and subjected them to chronic angiotensin II (Ang II) infusion or Adriamycin. Compared with control mice, Ksp-β-cat-/- mice were dramatically protected from proteinuria and glomerular damage. MMP-7, a downstream target of β-catenin, was upregulated in treated control mice, but this induction was blunted in the Ksp-β-cat-/- littermates. Incubation of isolated glomeruli with MMP-7 ex vivo led to nephrin depletion and impaired glomerular permeability. Furthermore, MMP-7 specifically and directly degraded nephrin in cultured glomeruli or cell-free systems, and this effect was dependent on its proteolytic activity. In vivo, expression or infusion of exogenous MMP-7 caused proteinuria, and genetic ablation of MMP-7 protected mice from Ang II-induced proteinuria and glomerular injury. Collectively, these results demonstrate that β-catenin-driven MMP-7 release from renal tubules promotes glomerular injury via direct degradation of the key slit diaphragm protein nephrin.

Renal sensory nerves increase sympathetic nerve activity and blood pressure in 2-kidney 1-clip hypertensive mice

Renal denervation lowers arterial blood pressure (ABP) in multiple clinical trials and some experimental models of hypertension. These antihypertensive effects have been attributed to the removal of renal afferent nerves. The purpose of the present study was to define the function, anatomy, and contribution of mouse renal sensory neurons to a renal nerve-dependent model of hypertension. First, electrical stimulation of mouse renal afferent nerves produced frequency-dependent increases in ABP that were eliminated by ganglionic blockade. Stimulus-triggered averaging revealed renal afferent stimulation significantly increased splanchnic, renal, and lumbar sympathetic nerve activity (SNA). Second, kidney injection of wheat germ agglutinin into male C57Bl6 mice (12-14 wk; Jackson Laboratories) produced ipsilateral labeling in the T11-L2 dorsal root ganglia. Next, 2-kidney 1-clip (2K1C) hypertension was produced in male C57Bl6 mice (12-14 wk; Jackson Laboratories) by placement of a 0.5-mm length of polytetrafluoroethylene tubing around the left renal artery. 2K1C mice displayed an elevated ABP measured via telemetry and a greater fall in mean ABP to ganglionic blockade at day 14 or 21 vs. day 0. Renal afferent discharge was significantly higher in 2K1C-clipped vs. 2K1C-unclipped or sham kidneys. In addition, 2K1C-clipped vs. 2K1C-unclipped or sham kidneys had lower renal mass and higher mRNA levels of several proinflammatory cytokines. Finally, both ipsilateral renal denervation (10% phenol) or selective denervation of renal afferent nerves (periaxonal application of 33 mM capsaicin) at time of clipping resulted in lower ABP of 2K1C mice at day 14 or 21. These findings suggest mouse renal sensory neurons are activated to increase SNA and ABP in 2K1C hypertension. NEW & NOTEWORTHY This study documents the function, anatomy, and contribution of mouse renal sensory nerves to neurogenic hypertension produced by renal stenosis. Activation of renal afferents increased sympathetic nerve activity and blood pressure. Renal afferent activity was elevated in hypertensive mice, and renal afferent denervation lowered blood pressure. Clinically, patients with renal stenosis have been excluded from clinical trials for renal denervation, but this study highlights the potential therapeutic efficacy to target renal nerves in these patients.

An Efficient Sieving Method to Isolate Intact Glomeruli from Adult Rat Kidney

Preservation of glomerular structure and function is pivotal in the prevention of glomerulonephritis, a category of kidney disease characterized by proteinuria which can eventually lead to chronic and end-stage renal disease. The glomerulus is a complex apparatus responsible for the filtration of plasma from the body. In disease, structural integrity is lost and allows for the abnormal leakage of plasma contents into the urine. A method to isolate and examine glomeruli in culture is critical for the study of these diseases. In this protocol, an efficient method of retrieving intact glomeruli from adult rat kidneys while conserving structural and morphological characteristics is described. This process is capable of generating high yields of glomeruli per kidney with minimal contamination from other nephron segments. With these glomeruli, injury conditions can be mimicked by incubating them with a variety of chemical toxins, including protamine sulfate, which causes foot process effacement and proteinuria in animal models. Degree of injury can be assessed using transmission electron microscopy, immunofluorescence staining, and western blotting. Nephrin and Wilms Tumor 1 (WT1) levels can also be assessed from these cultures. Due to the ease and flexibility of this protocol, the isolated glomeruli can be utilized as described or in a way that best suits the needs of the researcher to help better study glomerular health and structure in diseased states.

Abstract 081: Renal Sensory Nerves Increase Blood Pressure and Sympathetic Nerve Activity in 2-Kidney 1-Clip Hypertensive Mice

Renal denervation lowers arterial blood pressure (ABP) in multiple clinical trials and some experimental models of hypertension. These antihypertensive effects have been attributed to the removal of renal afferent nerves. The purpose of the present study was to determine whether renal sensory nerves contributed to the 2-Kidney-1-Clip (2K1C) model of hypertension. 2K1C hypertension was produced in male C57Bl6 mice (12-14 weeks, Jackson Laboratories) by placement of a 0.5mm length of PTFE tubing (ID: 0.008” x OD: 0.014”) around the left renal artery. 2K1C mice (n=6) displayed an elevated ABP measured via telemetry (Day 0: 96±4mmHg vs Day 14: 115±3mmHg, P<0.05). Ganglionic blockade with hexamethonium (30mg/kg, ip) produced a greater fall in mean ABP at Day 14 vs Day 0 (Day 0: -38±4mmHg vs Day 14: -51±4mmHg, P<0.05). Ipsilateral vs contralateral kidneys of 2K1C mice had lower mass (0.072±0.01g vs 0.163±0.02g, respectively; P<0.05) and higher mRNA levels of several pro-inflammatory cytokines (IL1B, IL2, IL10, TNFa; P<0.05). Both total renal denervation (10% phenol) or selective denervation of renal afferent nerves (periaxonal application of 33mM capsaicin) at time of clipping resulted in a lower ABP than 2K1C mice at Day 14 (2K1C: 115±3mmHg, phenol: 104±2mmHg, capsaicin: 105±3mmHg; P<0.05). Direct recording of renal afferent nerve activity showed significantly greater discharge in 2K1C versus control mice (control: 2.2±1.3Hz vs 2K1C: 61±12Hz, n=3/group; P<0.05). Furthermore, electrical stimulation of renal afferent nerves in control mice produced a frequency-dependent increase in ABP (5Hz: 3±1mmHg, 10Hz: 7±1mmHg, 20Hz: 12±2mmHg, n=4/group; P<0.05). These responses were eliminated after ganglionic blockade with 5mg/kg chlorisondamine (5Hz: 1±1mmHg, 10Hz: 1±1mmHg, 20Hz: 1±1mmHg; P<0.05). Stimulus-triggered averaging of SNA during stimulation of renal afferent nerves (1 Hz, 200uA) revealed significant (P<0.05, n=4/group) increases in splanchnic (221±28%), renal (195+15%), and lumbar (234±32%) SNA. Interestingly, the latency to the peak SNA (142±10ms) suggests supraspinal pathways mediate the sympathoexcitatory response. These findings suggest 2K1C hypertension depends on renal sensory nerves and elevated SNA via supraspinal pathways.

Trichotillomania resulting in a trichobezoar: a case report

This paper presents a case of a 19-year-old, 10 1/2-week-pregnant woman with trichotillomania that resulted in a trichobezoar. The case illustrates typical presentation, patient behavior, symptomatology, and physical findings of patients with trichobezoars. The hypothesized methods for trichobezoar formation, complications, and treatment are discussed. The diagnostic criteria, epidemiology, and treatment of trichotillomania are also discussed.

The outcome of intestinal fistulae: the Louisiana State University Medical Center--Shreveport experience

Fistulae arising from the intestinal tract are associated with significant morbidity and mortality rates. Most contemporary studies of fistulae report mortality rates between 6 and 20 per cent. The major causes of death in these patients are sepsis, electrolyte imbalance, and malnutrition. A total of 48 patients with either external or internal intestinal fistulae were reviewed in this study over a 5-year period at the Louisiana State University Medical Center at Shreveport. Intestinal fistulae were classified into three types, anatomic site, physiologic type, and etiology, to evaluate morbidity and mortality rates. We also attempted to evaluate the role of parenteral nutrition in this patient population, but our data were inconclusive because of the limited number of patients. There was no difference in mortality rates associated with anatomical sites. High-output fistulae were associated with a higher mortality rate compared to low-output fistulae. Fifty-six per cent of the patients achieved closure. The overall mortality rate was 21 per cent. Spontaneous closure rates were lower when compared to those in other studies. This was attributed to sepsis, malignancy, and history of previous radiation therapy. Management of intestinal fistulae includes control of sepsis, correction of electrolyte disturbances, nutritional support, and operative intervention if necessary.

Snake bite poisoning in pregnancy. A review of the literature

With our 2 cases, there are 30 reported cases in English of snake bite poisoning in pregnancy with some details presented and 20 cases without details, for a total of 50 cases. We reviewed the maternal and fetal outcomes in the 30 cases that had such information. Poisoning by members of the Crotalidae family (rattlesnakes, cotton-mouths [water moccasins] and copperheads) during pregnancy carries with it a fetal wastage rate of 43% and a maternal mortality rate of 10%. Pit viper bites cause a bleeding diathesis from the fact that the venom of these snakes contains a procoagulant that defibrinates the blood and leads to bleeding throughout the body.

Indigenous amebiasis

A case of amebic anemia in a 53-year-old Louisianian prompted us to report it, in order to create awareness of such cases occurring in the absence of foreign travel. If one is cognizant of amebiasis it will be included in the differential diagnosis when it is proper to do so.

Retroperitoneal necrotizing fasciitis

We present a case of retroperitoneal necrotizing fasciitis treated by urgent abdomino-perineal resection of the rectum with permanent colostomy. We can find no prior case in the English literature treated in this manner. Retroperitoneal occurrence of this disease is unusual. The process originated from perianal sepsis following chemotherapy for head and neck cancer.

Spontaneous biliary enteric fistulas

Biliary enteric fistulas usually occur as a complication of chronic cholelithiasis, may be difficult to document preoperatively, and often pose problems in surgical management. We reviewed 13 cases of spontaneous biliary enteric fistulas to identify methods of diagnosis, management, and complications. There was no specific set of clinical symptoms or signs that led to the diagnosis of a fistula. In six cases the diagnosis was made preoperatively by x-ray films showing pneumobilia, gallstone in the small bowel, or fistula. Initial surgical treatment included cholecystectomy in six cases, small bowel enterotomy and removal of gallstones in four, and vagotomy and antrectomy in one case. Two patients initially treated without operation were lost to follow-up. Eight complications occurred in six patients, and there were three deaths due to underlying cardiac disease. The morbidity and mortality of biliary enteric fistulas associated with chronic cholecystitis may be avoided by performing elective cholecystectomy when the patient is in optimal condition.