Physiology and pathophysiology of the vasopressin-regulated renal water reabsorption

To prevent dehydration, terrestrial animals and humans have developed a sensitive and versatile system to maintain their water homeostasis. In states of hypernatremia or hypovolemia, the antidiuretic hormone vasopressin (AVP) is released from the pituitary and binds its type-2 receptor in renal principal cells. This triggers an intracellular cAMP signaling cascade, which phosphorylates aquaporin-2 (AQP2) and targets the channel to the apical plasma membrane. Driven by an osmotic gradient, pro-urinary water then passes the membrane through AQP2 and leaves the cell on the basolateral side via AQP3 and AQP4 water channels. When water homeostasis is restored, AVP levels decline, and AQP2 is internalized from the plasma membrane, leaving the plasma membrane watertight again. The action of AVP is counterbalanced by several hormones like prostaglandin E2, bradykinin, dopamine, endothelin-1, acetylcholine, epidermal growth factor, and purines. Moreover, AQP2 is strongly involved in the pathophysiology of disorders characterized by renal concentrating defects, as well as conditions associated with severe water retention. This review focuses on our recent increase in understanding of the molecular mechanisms underlying AVP-regulated renal water transport in both health and disease

Renal compensation to chronic hypoxic hypercapnia: downregulation of pendrin and adaptation of the proximal tubule.

Contains fulltext : 51556.pdf (publisher's version ) (Open Access)The molecular basis for the renal compensation to respiratory acidosis and specifically the role of pendrin in this condition are unclear. Therefore, we studied the adaptation of the proximal tubule and the collecting duct to respiratory acidosis. Male Wistar-Hannover rats were exposed to either hypercapnia and hypoxia [8% CO(2) and 13% O(2) (hypercapnic, n = 6) or normal air (controls, n = 6)] in an environmental chamber for 10 days and were killed under the same atmosphere. In hypercapnic rats, arterial pH was lower than controls (7.31 +/- 0.01 vs. 7.39 +/- 0.01, P = 0.03), blood HCO(3)(-) concentration was increased (42 +/- 0.9 vs. 32 +/- 0.24 mM, P < 0.001), arterial Pco(2) was increased (10.76 +/- 0.4 vs. 7.20 +/- 0.4 kPa, P < 0.001), and plasma chloride concentration was decreased (92.2 +/- 0.7 vs. 97.2 +/- 0.5 mM, P < 0.001). Plasma aldosterone levels were unchanged. In the proximal tubule, immunoblotting showed an increased expression of sodium/bicarbonate exchanger protein (188 +/- 22 vs. 100 +/- 11%, P = 0.005), confirmed by immunohistochemistry. Total Na/H exchanger protein expression in the cortex was unchanged by immunoblotting (119 +/- 10 vs. 100 +/- 11%, P = 0.27) and immunohistochemistry. In the cortex, the abundance of pendrin was decreased (51 +/- 9 vs. 100 +/- 7%, P = 0.003) by immunoblotting. Immunohistochemistry revealed that this decrease was clear in both cortical collecting ducts (CCDs) and connecting tubules (CNTs). This demonstrates that pendrin expression can be regulated in acidotic animals with no changes in aldosterone levels and no external chloride load. This reduction of pendrin expression may help in redirecting the CNT and CCD toward chloride excretion and bicarbonate reabsorption, contributing to the increased plasma bicarbonate and decreased plasma chloride of chronic respiratory acidosis

Human antigen-presenting cells respond differently to gut-derived probiotic bacteria but mediate similar strain-dependent NK and T cell activation

The intestinal microbiota is essential for development and homeostasis of the local and systemic immune system, and particularly strains of lactic acid bacteria and Escherichia coli have been shown to have balancing effects on inflammatory conditions such as allergy and inflammatory bowel disease. However, distinct strains possess different potential to polarise and regulate the immune response, and in vitro results used to choose strains for therapeutic purposes may depend strongly on the cell type used as a model. We compared the response of three types of human antigen-presenting cells (blood myeloid dendritic cells, monocyte-derived dendritic cells and monocytes) to strains of intestinal bacteria, and characterised the effector response of natural killer cells and naïve T cells. The response to gut-derived bacteria was markedly different between antigen-presenting cells as concerns maturation and induction of pro-inflammatory cytokines, with blood dendritic cells and monocytes responding with production of interleukin-6 and tumour necrosis factor- to strains, which elicited anti-inflammatory responses in monocyte-derived dendritic cells. In contrast, an interferon- inducing capability of antigen-presenting cells cultured with specific bacterial strains and an interferon--inhibitory capability of other strains were generally observable with all types of antigen-presenting cells, and in both natural killer cells and T cells

Acute growth hormone administration induces antidiuretic and antinatriuretic effects and increases phosphorylation of NKCC2.

Contains fulltext : 53076.pdf (publisher's version ) (Open Access)Growth hormone (GH) has antidiuretic and antinatriuretic effects in rats and humans, but the molecular mechanisms responsible for these effects are unknown. The aim of this study was to investigate the mechanisms behind the acute renal effects of GH in rats. Female rats received rat (r)GH (2.8 mg/kg sc) or saline and were placed in metabolic cages for 5 h. Urinary excretion of electrolytes and urinary volume were reduced after rGH injection, while urine osmolality was increased. Creatinine and lithium clearance remained unchanged, suggesting that rGH increases reabsorption in segments distal to the proximal tubule. Total plasma insulin-like growth factor I (IGF-I) levels did not change, while cortical IGF-I mRNA abundance was increased. The relative abundance of total and Ser(256)-phosphorylated aquaporin 2 was found to be unchanged by immunoblotting, whereas a significant increase of Thr(96) and Thr(101)-phosphorylated NKCC2 (renal Na(+), K(+), 2Cl(-) cotransporter) was found in the inner stripe of outer medulla thick ascending limbs (mTAL). Additionally, an increased NKCC2 expression was observed in the cortical region. Immunohistochemistry confirmed these findings. The density of NKCC2 molecules in the apical membrane of mTAL cells appeared to be unchanged after rGH injection evaluated by immunoelectron microscopy. Basolateral addition of rGH or IGF-I to microperfused rat mTAL segments did not change transepithelial voltage. In conclusion, GH appears to exert its acute antinatriuretic and antidiuretic effects through indirect activation of NKCC2 in the mTAL

Mannan Enhances IL-12 Production by Increasing Bacterial Uptake and Endosomal Degradation in L. acidophilus and S. aureus Stimulated Dendritic Cells

The mannose receptor (MR) is a C-type lectin involved in endocytosis and with a poorly defined ability to modulate cellular activation. We investigated the effect of mannan treatment prior to stimulation of murine bone marrow-derived dendritic cells with the Gram-positive bacteria Lactobacillus acidophilus NCFM (L. acidophilus) on the induction of Interleukin (IL)-12. Mannan enhanced the IL-12 production induced by L. acidophilus in a dose dependent manner (up to 230% enhancement). Additionally, mannan-enhanced IL-12 induction was also demonstrated with another Gram-positive bacteria, Staphylococcus aureus (S. aureus), while an IL-12 reducing effect was seen on Escherichia coli stimulated cells. Furthermore, the expression of Interferon \u3b2 (Ifnb) was increased in cells treated with mannan prior to stimulation with L. acidophilus. The addition of mannan but not of bacteria led to endocytosis of MR, while addition of mannan prior to L. acidophilus or S. aureus resulted in increased endocytosis of bacteria, a faster killing of endocytosed bacteria, and increased reactive oxygen species production. Expression of signaling lymphocytic activation molecule (SLAMF)1 shown previously to be involved in the facilitation of endosomal degradation was upregulated by mannan but not by L. acidophilus and S. aureus. The IL-12 enhancement by mannan but not the IL-12 induced by the bacteria was abrogated by addition of inhibitors of clathrin coated pits (chlorpromazine and monodansylcadaverine). Furthermore, the addition of acid sphingomyelinase, a facilitator of ceramide raft formation, prior to addition of L. acidophilus enhanced the IL-12 production and the endocytosis of bacteria. In summary, our results show that mannan increases the IL-12 production induced by some Gram-positive bacteria through MR-endocytosis, which increases bacterial endocytosis and endosomal killing. The differential effect of MR activation on the IL-12 production induced by Gram-positive and Gram-negative bacteria may influence the immune response toward allergens and other glycoproteins

DENATURATION AT INTERFACES AFFECTS IMMUNOREACTIVITY OF &#946;-LACTOGLOBULIN AND ITS CELLULAR UPTAKE BY MONOCYTES

Bovine \uf062-lactoglobulin (\u3b2-LG) is the major protein in bovine whey, but it is not found in human milk. It belongs to the lipocalin protein family, and is one of the major milk allergens. At physiological pH BLG is a dimer consisting of two identical amino acid chains (162 amino acids) each having a molecular mass about 18 kDa. \u3b2-LG is an exceptionally acid-stable protein. At pH 2 it dissociates reversibly into monomers, but its structure remains native. Furthermore, native \u3b2-LG is almost totally resistant to pepsin degradation at low pH. Resistance to acid hydrolysis as well as to proteases allows some of the \u3b2-LG to remain intact after digestion. This increases the probability that intact \u3b2-LG as well as its digested fragments will be absorbed as antigens. The spontaneous adsorption of protein molecules on interfaces is an ubiquitous phenomenon in natural and man-made systems. The structural rearrangement caused by the direct contact with the sorbent phase may affect protein biological activity, including bioavailability, and ability to bind micro- and macromolecular ligands. Moreover, protein immunoreactivity has been assessed to change if protein molecules interact with an hydrophobic phase. The aim of this work is to understand whether and how the \u3b2-LG conformational changes derived from the interaction with a hydrophobic interfaces - that consist in our case in an oil-in-water nanoemulsion - can modulate its immunoreactivity and its absorption behavior by human cells involved in the immuno response Competitive ELISA measurements, carried out using specific monoclonal antibodies, prove that \u3b2-LG increase dramatically its immunoreactivity after interaction with the hydrophobic surface, giving the evidences that the protein, after the conformational rearrangement coming from the absorption, should be recognised in different way compared with the native one. The interfacial denaturation changes also the protein uptake behaviour by human monocytes. We carried out experiments using monocytes from a MonoMac6 cell line and a FITC-labeled \u3b2-LG. Uptake kinetics were recorded using flow cytometry and cell confocal microscopy pictures were taken. Results show that the native free protein is internalized by the cells, and a heat denaturation process seems to do not interferer on the internalizeted \u3b2-LG final amount and kinetics. Moreover the presence of 10 and 50 molar excess of unlabeled free protein seems to not influence the protein uptake. Surface denatured \u3b2-LG is internalizated by monocytes more efficiently and rapidity. The uptake of this protein form is influenced by the presence unlabeled free \u3b2-LG, as visible by a general slowing-down of the internalization rate. Furthermore the internalization of the FITC-labeled \u3b2-LG is not influenced by the presence of unlabeled protein staked on the oil droplets. All these results point the importance of the physical form of a potential allergen on its immunoreactivity response and uptake behaviour, as the fact that the natural form of this allergen in whole milk and dairy products is often in complex with a lipid matrix. Future studies will be aimed to study the behaviour of other cells from the immunosystem after the contact with \u3b2-LG adsorbed on this hydrophobic surface