Hypoxia inducible factor (HIF) prolyl-4-hydroxylase domain-containing proteins (PHDs) promote the degradation of HIF-1␣. Because HIF-1␣ is highly expressed in the renal medulla and HIF-1␣-targeted genes such as nitric oxide synthase, cyclooxygenase, and heme oxygenase are important in the regulation of renal medullary function, we hypothesized that PHD regulates HIF-1␣ levels in the renal medulla and, thereby, participates in the control of renal Na ϩ excretion. Using real-time RT-PCR, Western blot, and immunohistochemical analyses, we have demonstrated that all three isoforms of PHD, PHD1, PHD2, and PHD3, are expressed in the kidneys and that PHD2 is the most abundant isoform. Regionally, all PHDs exhibited much higher levels in renal medulla than cortex. A furosemide-induced increase in renal medullary tissue PO2 significantly decreased PHD levels in renal medulla, whereas hypoxia significantly increased mRNA levels of PHDs in cultured renal medullary interstitial cells, indicating that O2 regulates PHDs. Functionally, the PHD inhibitor L-mimosine (L-Mim, 50 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 ip for 2 wk) substantially upregulated HIF-1␣ expression in the kidneys, especially in the renal medulla, and remarkably enhanced (by Ͼ80%) the natriuretic response to renal perfusion pressure in Sprague-Dawley rats. Inhibition of HIF transcriptional activity by renal medullary transfection of HIF-1␣ decoy oligodeoxynucleotides attenuated L-Mim-induced enhancement of pressure natriuresis, which confirmed that HIF-1␣ mediated the effect of L-Mim. These results indicate that highly expressed PHDs in the renal medulla make an important contribution to the control of renal Na ϩ excretion through regulation of HIF-1␣ and its targeted genes. fluid homeostasis; anoxia; natriuretic factor; gene transcription; renal tubules; renal hemodynamics IT IS WELL KNOWN that PO 2 is much lower in the renal medulla than in the renal cortex because of relative "underperfusion," the countercurrent O 2 diffusion between descending and ascending vasa recta, and the high metabolic ion transport activity of the thick ascending limb of Henle in the renal medullary region (6, 10). To adapt to this low-PO 2 milieu, the renal medulla has naturally developed various mechanisms to protect the cells from ischemic and hypoxic injury (5,6,15) and to ensure that the cells in this kidney region function normally in a hypoxic environment (6, 10). Increase in tissue blood perfusion to facilitate the O 2 supply and inhibition of tubular metabolic activity to decrease O 2 demands (5,6,15,53) are the common outcomes of various adaptive actions induced by different renal medullary factors such as nitric oxide (NO), prostaglandins, and heme oxygenase (HO) products. Hypoxia inducible factor (HIF)-1␣, the master regulator of adaptation to hypoxia, has been shown to activate gene transcription of many O 2 -sensitive genes such as NO synthase (NOS), cyclooxygenase (COX), HO, and vascular endothelial growth factor (21,25,26,32,38,45,50,53). The participation of the products controlled...

Factor H (fH) is an important regulator of the alternative complement cascade. Several human pathogens have been shown to bind fH to their surface, a process that facilitates immune evasion or cell to cell interaction. Among the pathogens that bind fH are some Borrelia species associated with Lyme disease and relapsing fever. The fH-binding proteins of the Lyme spirochetes form two classes (I and II). In Borrelia burgdorferi B31MI, class I includes the outer surface protein E (OspE) paralogs, L39, N38, and P38, whereas the class II group includes A68 and additional proteins that have not yet been identified. To identify the OspE determinants involved in fH and OspE-targeting infection-induced Ab (iAb) binding, deletion, random, and site-directed mutagenesis of L39 were performed. Mutations in several different regions of L39 abolished fH and or iAb binding, indicating that separable domains and residues of OspE are required for ligand binding. Some of the mutants that lost the ability to bind fH, iAb, or both had only a single amino acid change. Site-directed mutagenesis of three putative coiled coil motifs of OspE revealed that these higher order structures are required for fH binding but not for iAb binding. The data presented within demonstrate that the binding of fH and iAb to the OspE protein is mediated by higher order structures and protein conformation. These studies advance our understanding of fH binding as a virulence mechanism and facilitate ongoing efforts to use fH-binding proteins in the development of microbial vaccines.

The binding of Borrelia burgdorferi OspE, OspF, and family 163 (Elp) proteins to factor H/factor H-like protein 1 (FHL-1) and other serum proteins from different animals was assessed. OspE paralogs bound factor H and unidentified serum proteins from a subset of animals, while OspF and Elp proteins did not. These data advance our understanding of factor H binding, the host range of the Lyme spirochetes, and the expanding role of OspE in pathogenesis.