Genetic modulation of diabetic nephropathy among mouse strains with Ins2 Akita mutation.

Diabetic nephropathy (DN) is a major complication of diabetes and the leading cause of end-stage renal disease. DN is characterized by changes in kidney structure and function but the underlying genetic and molecular factors are poorly understood. We used a mouse diversity panel to explore the genetic basis of DN traits in mice carrying the Ins2 Akita mutation. Twenty-eight Akita strains were generated by breeding this panel to DBA/2.Akita mice. Male F1 diabetic and nondiabetic littermates were evaluated for DN-related traits. Urine albumin-to-creatinine ratios (ACRs), volume and cystatin C as well as blood urea nitrogen and lipoprotein levels varied significantly among the diabetic strains. For most Akita strains, ACR values increased 2- to 6-fold over euglycemic control values. However, six strains exhibited changes in ACR exceeding 10-fold with two strains (NOD/ShiLt and CBA) showing 50- to 83- fold increases. These increases are larger than previously reported among available DN mouse models establishing these strains as useful for additional studies of renal function. ACRs correlated with cystatin C (P = 0.0286), a measure of hyperfiltration and an interstitial tubular marker associated with DN onset in humans suggesting that tubule damage as well as podocyte-stress contributed to reduced kidney function assessed by ACR. Although large changes were seen for ACRs, severe nephropathology was absent. However, glomerular hypertrophy and collagen IV content were found to vary significantly among strains suggesting a genetic basis for early onset features of DN. Our results define the range of DN phenotypes that occur among common inbred strains of mice.

RNA-binding protein IGF2BP2/IMP2 is required for laminin-ß2 mRNA translation and is modulated by glucose concentration.

Laminin-ß2 (LAMB2) is a critical component of the glomerular basement membrane as content of LAMB2 in part determines glomerular barrier permeability. Previously, we reported that high concentrations of glucose reduce expression of this laminin subunit at the translational level. The present studies were undertaken to further define systems that control Lamb2 translation and the effect of high glucose on those systems. Complementary studies were performed using in vitro differentiation of cultured podocytes and mesangial cells exposed to normal and elevated concentrations of glucose, and tissues from control and diabetic rats. Together, these studies provide evidence for regulation of Lamb2 translation by IMP2, an RNA binding protein that targets Lamb2 mRNA to the actin cytoskeleton. Expression of Imp2 itself is regulated by the transcription factor HMGA2, which in turn is regulated by the microRNA let-7b. Elevated concentrations of glucose increase let-7b, which reduces HMGA2 expression, in turn reducing IMP2 and LAMB2. Correlative changes in kidney tissues from control and streptozotocin-induced diabetic rats suggest these control mechanisms are operative in vivo and may contribute to proteinuria in diabetic nephropathy. To our knowledge, this is the first time that translation of Lamb2 mRNA has been linked to the actin cytoskeleton, as well as to specific RNA-binding proteins. These translational control points may provide new targets for therapy in proteinuric disorders such as diabetic nephropathy where LAMB2 levels are reduced.

Role of the mTOR pathway in LPS-activated monocytes: influence of hypertonic saline.

BACKGROUND: As heightened protein synthesis is the hallmark of many inflammatory syndromes, we hypothesize that the mammalian target of rapamycin (mTOR) pathway, which control the cap-dependent translation initiation phase, was activated by lipopolysaccharide (LPS). In addition, we studied the effect of hypertonic saline solution (HTS) on the mTOR cascade in peripheral blood mononuclear cells (PBMCs). MATERIALS AND METHODS: PBMCs were isolated from healthy volunteers and treated with LPS. Cells were pretreated with phosphatidylinositol 3-kinase (PI3K) and mTOR inhibitors, or with HTS. Supernatants were harvested 20 h following LPS treatment, and interleukin-10 (IL-10), interleukin-6 (IL-6) and tumor necrosis alpha (TNFα) were analyzed by ELISA. Immunoblot experiments were performed for components of the PI3K/Akt/mTOR pathway at various time points. RNA was extracted after 90 min for real-time RT-PCR quantification. RESULTS: The mTOR pathway is activated in PBMCs within 1 h of LPS stimulation. Pretreatment with rapamycin, a specific inhibitor of mTOR, resulted in a significant decrease of IL-10 and IL-6 translation and expression but did not affect the LPS-induced TNFα production. Both the mTOR pathway and the LPS-induced IL-6 production were down-regulated by HTS pretreatment. CONCLUSIONS: The PI3k/Akt/mTOR cascade modulates LPS-induced cytokines production differentially. IL-10 and IL-6 expression are both up-regulated by activation of the mTOR pathway in response to LPS in PBMCs, while TNFα is not controlled by the mTOR cascade. Meanwhile, pretreatment of PBMCs with a HTS solution suppresses mTOR activity as well as LPS-induced IL-6, suggesting a more central role for mTOR as a regulator of the immuno-inflammatory response.

Early elevation in random plasma IL-6 after severe injury is associated with development of organ failure.

Excessive proinflammatory activation after trauma plays a role in late morbidity and mortality, including the development of multiple organ dysfunction syndrome (MODS). To date, identification of patients at risk has been challenging. Results from animal and human studies suggest that circulating interleukin 6 (IL-6) may serve as a biomarker for excessive inflammation. The purpose of this analysis was to determine the association of IL-6 with outcome in a multicenter developmental cohort and in a single-center validation cohort. Severely injured patients with shock caused by hemorrhage were evaluated within a multicenter developmental cohort (n = 79). All had blood drawn within 12 h of injury. Plasma IL-6 was determined by multiplex proteomic analysis. Clinical and outcome data were prospectively obtained. Within this developmental cohort, a plasma IL-6 level was determined for the subsequent development of MODS by developing a receiver operating curve and defining the optimal IL-6 level using the Youden Index. This IL-6 level was then evaluated within a separate validation cohort (n = 56). A receiver operating curve was generated for IL-6 and MODS development, with an IL-6 level of 350 pg/mL having the highest sensitivity and specificity within the developmental cohort. IL-6 was associated with MODS after adjusting for Acute Physiology and Chronic Health Evaluation, Injury Severity Score, male sex, and blood transfusions with an odds ratio of 3.9 (95% confidence interval, 1.33 - 11.19). An IL-6 level greater than 350 pg/mL within the validation cohort was associated with an increase in MODS score, MODS development, ventilator days, intensive care unit length of stay, and hospital length of stay. However, this IL-6 level was not associated with either the development of nosocomial infection or mortality. Elevation in plasma IL-6 seems to correlate with a poor prognosis. This measurement may be useful as a biomarker for prognosis and serve to identify patients at higher risk of adverse outcome that would benefit from novel therapeutic interventions.

Mechanisms and control of protein translation in the kidney.

Translational control of protein synthesis is critical for cell division, homeostasis and survival. Recent data indicate that dysregulation of protein synthesis that leads to either increased or decreased expression of specific proteins contributes to the manifestations of various kidney diseases. Most of the control of protein synthesis occurs in the first or initiation phase, which is also the most complicated. Following the initiation phase is the elongation phase where the peptide chain is formed. RNA transcripts are released from ribosomes after the termination phase. Transcripts can be translated in a cap-dependent or cap-independent manner. The mTOR (mammalian target of rapamycin) cascade regulates translation of most cap-dependent transcripts at the level of initiation and elongation, which represents 95% of total transcripts. During specific events (e.g. mitosis, stress cell survival) control of the less-common cap-independent transcripts occurs which allows the cell to adapt to the new state. Activation of stress kinases and inactivation of the mTOR pathway are at the center of this adaptive mechanism. Recent studies have elucidated the role of micro-RNAs (miRs) in controlling translation. miRs bind directly to specific transcripts and most often directly reduce translation; however, by targeting other positive or negative regulators of the pathways regulating protein synthesis they may indirectly affect synthetic levels of other transcripts. Several examples are described below in which these mechanisms are intertwined and act together to dysregulate protein synthesis in the diseased kidney.

Reductions in laminin beta2 mRNA translation are responsible for impaired IGFBP-5-mediated mesangial cell migration in the presence of high glucose.

Insulin-like growth factor binding protein-5 (IGFBP-5) mediates mesangial cell migration through activation of cdc42, and laminin421 binding to alpha(6)beta(1)-integrin (Berfield AK, Hansen KM, Abrass CK. Am J Physiol Cell Physiol 291: C589-C599, 2006). Because glomerular expression of laminin beta(2) is reduced in diabetic rats (Abrass CK, Spicer D, Berfield AK, St. John PL, Abrahamson DR. Am J Pathol 151: 1131-1140, 1997), we directly examined the effect of hyperglycemia on mesangial cell migration and laminin beta2 expression. Migration mediated by IGFBP-5 is impaired in the presence of 25 mM glucose. This reduction in migration was found to result from a loss in mesangial cell synthesis of laminin421, and IGFBP-5-induced migration could be restored by replacing laminin421. Additional studies showed that there was selective reduction in mRNA translation of laminin beta2 in the presence of high glucose. Preserved synthesis of laminin beta1 indicates that not all proteins are reduced by high glucose and confirms prior data showing that laminin411 cannot substitute for laminin421 in IGFBP-5-mediated migration. Given the importance of mesangial migration in the reparative response to diabetes-associated mesangiolysis, these findings provide new insights into abnormalities associated with diabetic nephropathy and the potential importance of differential control of protein translation in determination of alterations of protein expression.

The priming effect of C5a on monocytes is predominantly mediated by the p38 MAPK pathway.

The dysregulation of the inflammatory response after trauma leads to significant morbidity and mortality. Monocytes and macrophages play a central role in the orchestration of the inflammatory response after injury. Serum interleukin-6 (IL-6) concentration correlates with poor outcomes after injury. Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine that plays a crucial role in the pathogenesis of multiple organ dysfunction syndrome. Furthermore, in the presence of C5a, monocytes and macrophages have potentiated responses, but the mechanisms underlying this response remain largely unknown. Peripheral blood mononuclear cells (PBMCs) were isolated from healthy volunteers and pretreated with C5a (100 ng/mL) for 1 h before adding lipopolysaccharide (LPS) (10 ng/mL) for up to 20 h. Inhibitors for the mitogen-activated protein kinases (MAPKs) were added 1 h before adding C5a. C5a primes monocytes for LPS-induced IL-6 and TNF-alpha production. Treatment of PBMCs with C5a leads to a rapid activation of the 3 MAPK pathways. SP600125 (inhibitor of c-Jun NH2-terminal kinase MAPK) and PD98059 (inhibitor of extracellular signal-regulated kinase MAPK) did not affect the C5a priming of the LPS-induced IL-6 and TNF-alpha production, whereas SB203580, a specific inhibitor of p38 MAPK, did suppress the C5a priming effect. These results demonstrate that C5a primes adherent PBMCs and modulates LPS-induced IL-6 and TNF-alpha production. Results from extracellular signal-regulated kinase and c-Jun NH2-terminal kinase MAPK blockade suggest that these signaling pathways have minimal or no role in reprogramming LPS-mediated IL-6 and TNF-alpha production. On the contrary, in PBMCs, C5a activates the p38 cascade, and this pathway plays a major role in the C5a enhancement of LPS-induced IL-6 and TNF-alpha production.

Notch signaling through tramtrack bypasses the mitosis promoting activity of the JNK pathway in the mitotic-to-endocycle transition of Drosophila follicle cells.

BACKGROUND: The follicle cells of the Drosophila egg chamber provide an excellent model in which to study modulation of the cell cycle. During mid-oogenesis, the follicle cells undergo a variation of the cell cycle, endocycle, in which the cells replicate their DNA, but do not go through mitosis. Previously, we showed that Notch signaling is required for the mitotic-to-endocycle transition, through downregulating String/Cdc25, and Dacapo/p21 and upregulating Fizzy-related/Cdh1. RESULTS: In this paper, we show that Notch signaling is modulated by Shaggy and temporally induced by the ligand Delta, at the mitotic-to-endocycle transition. In addition, a downstream target of Notch, tramtrack, acts at the mitotic-to-endocycle transition. We also demonstrate that the JNK pathway is required to promote mitosis prior to the transition, independent of the cell cycle components acted on by the Notch pathway. CONCLUSION: This work reveals new insights into the regulation of Notch-dependent mitotic-to-endocycle switch.

Notch-dependent Fizzy-related/Hec1/Cdh1 expression is required for the mitotic-to-endocycle transition in Drosophila follicle cells.

During Drosophila oogenesis, Notch function regulates the transition from mitotic cell cycle to endocycle in follicle cells at stage 6. Loss of either Notch function or its ligand Delta (Dl) disrupts the normal transition; this disruption causes mitotic cycling to continue and leads to an overproliferation phenotype. In this context, the only known cell cycle component that responds to the Notch pathway is String/Cdc25 (Stg), a G2/M cell cycle regulator. We found that prolonged expression of string is not sufficient to keep cells efficiently in mitotic cell cycle past stage 6, suggesting that Notch also regulates other cell cycle components in the transition. By using an expression screen, we found such a component: Fizzy-related/Hec1/Cdh1 (Fzr), a WD40 repeat protein. Fzr regulates the anaphase-promoting complex/cyclosome (APC/C) and is expressed at the mitotic-to-endocycle transition in a Notch-dependent manner. Mutant clones of Fzr revealed that Fzr is dispensable for mitosis but essential for endocycles. Unlike in Notch clones, in Fzr mutant cells mitotic markers are absent past stage 6. Only a combined reduction of Fzr and ectopic Stg expression prolongs mitotic cycles in follicle cells, suggesting that these two cell cycle regulators, Fzr and Stg, are important mediators of the Notch pathway in the mitotic-to-endocycle transition.