Long-term ammonium chloride or sodium bicarbonate treatment in two models of polycystic kidney disease.

Administration of ammonium chloride aggravates, while short-term administration of sodium or potassium bicarbonate lessens the development of polycystic kidney disease in Han:SPRD rats. We have conducted studies to determine whether the protection afforded by the administration of sodium bicarbonate is sustained and prevents development of uremia during chronic administration and whether the effects of the administration of ammonium chloride and sodium bicarbonate are also observed in a different model of polycystic kidney disease, the CD1-pcy/pcy mouse. We found that chronic administration of 200 mM sodium bicarbonate to Han:SPRD rats inhibited cystic enlargement and prevented the subsequent development of interstitial inflammation, chronic fibrosis, and uremia. We also found that, while the administration of ammonium chloride has similar effects in Han:SPRD rats and CD1-pcy/pcy mice, the administration of sodium bicarbonate is only protective in the Han:SPRD rats. This probably reflects differences in these models (predominately involvement of proximal tubules in Han:SPRD rats and of collecting ducts and distal tubules in pcy/pcy mice) and the different location and nature of the renal metabolic responses to the administration of acid or alkaline load.

Developmental expression of urine concentration-associated genes and their altered expression in murine infantile-type polycystic kidney disease.

Currently, there is little understanding of what factors regulate the development of urine concentrating capability in normal or polycystic kidney. The present study examined the developmental expression of genes associated with urine concentration in developing mice, including C57BL/6J-cpk/cpk mice with autosomal recessive-infantile (AR) polycystic kidney disease (PKD). Concentration of urine requires: 1) medullary collecting ducts (CD) located within a hypertonic interstitium, 2) CD cell expression of functional arginine vasopressin V2 receptors (AVP-V2R), and 3) the presence of appropriate CD water channels (aquaporins, AQP 2 and 3). An increase in urine osmolarity, normally seen between 1 and 3 weeks of age, was absent in cpk cystic mice. Aldose reductase mRNA expression (a gene upregulated by medullary hyperosmolarity) increased in normal mice, but remained low in the cystic kidney, suggesting the absence of a hypertonic medullary interstitium. AVP-V2R, AQP2, and AQP3 mRNA expression normally increase between 7 and 14 days. However, all were dramatically overexpressed even at 7 days of age in the cpk kidney in vivo, but decreased in vitro. Activation of the AVP-V2 receptor stimulates the production of cAMP, a substance known to promote cyst enlargement. To determine if CD cAMP, generated from increased AVP-V2Rs, was accelerating the PKD, cystic mice and their normal littermates were treated with OPC31260, a relatively specific AVP-V2R antagonist. OPC31260 treatment of cystic mice led to an amelioration of the cystic enlargement and azotemia. Treatment also decreased renal AQP2 mRNA but increased AVP-V2R and AQP3 mRNA expression in vivo. AVP upregulates the expression of AVP-V2R, AQP2, and AQP3 mRNAs in vitro. Renal EGF, known to inhibit AVP-V2R activity, downregulates AVP-V2R mRNA in vitro. Brief in vivo EGF treatment, known to decrease PKD in cpk mice, led to increased expression of AVP-V2R, AQP2, and AQP3 mRNAs at 2 weeks in both normal and cystic mice but no change was evident at 3 weeks of age. In conclusion, the development of urinary concentration ability correlates with the development of an increased medullary osmotic gradient which is diminished in murine ARPKD. However, CD genes associated with this process are overexpressed in vivo but underexpressed in vitro in the cystic kidney. The overexpression and/or overactivity of the AVP-V2R appears to contribute to the progression of PKD since an AVP-V2R antagonist inhibits cystic renal enlargement in the cpk mouse.

Early phosphorylation of the retinoblastoma gene product regulates protein binding to the c-fos retinoblastoma control element during T cell activation.

Function of the retinoblastoma tumor suppressor protein [pRb] is regulated by phosphorylation during the G1 and S phases of the cell cycle. pRb regulates transcription of several genes, including c-fos. However, since c-fos is regulated during exit from G0, it has remained unclear how pRb participates in c-fos regulation. We have identified a protein complex, the retinoblastoma control factor A [RCF-A] which binds to the c-fos retinoblastoma control element [RCE] and is regulated by pRb within 10 min after T cell activation. We demonstrate that pRb control of RCF-A is dependent upon the state of phosphorylation of pRb. pRb becomes hyperphosphorylated on specific peptides at 10 min after mitogenic stimulation and pRb is dephosphorylated by 30 min. This time course coincides with RCF-A DNA binding. RCF-A binds RCE DNA longer when cells are treated with okadaic acid, and okadaic acid prevents pRb dephosphorylation. Dephosphorylated pRb inhibits RCF-A binding in vitro but phosphorylated pRb does not. Thus, in addition to the described G1/S regulation of pRb, transient inactivation by phosphorylation of pRb in T cells may also be important as resting cells leave G0.