Filling the holes in cystic kidney disease research

Kidney disease is a significant medical and public health problem. The National Institute of Diabetes and Digestive and Kidney Diseases recently asked the community to identify research objectives, which, if addressed, could improve understanding of basic kidney function and aid in prevention, treatment, and reversal of kidney disease. The Kidney Research National Dialogue invited interested parties to submit, discuss, and prioritize ideas using an interactive website; 1600 participants posted more than 300 ideas covering all areas of kidney disease, including the cystic kidney diseases. Although much is known about the genetics and pathogenesis of cystic diseases, there remain challenges to our understanding of the fundamental mechanisms of cyst formation, what genes act as modifiers to cause variable responses in different people, and how to detect and monitor disease progression. This article summarizes key research questions for cystic kidney diseases.

Glomerular hyperfiltration: definitions, mechanisms and clinical implications

Glomerular hyperfiltration is a phenomenon that can occur in various clinical conditions including kidney disease. No single definition of glomerular hyperfiltration has been agreed upon, and the pathophysiological mechanisms, which are likely to vary with the underlying disease, are not well explored. Glomerular hyperfiltration can be caused by afferent arteriolar vasodilation as seen in patients with diabetes or after a high-protein meal, and/or by efferent arteriolar vasoconstriction owing to activation of the renin-angiotensin-aldosterone system, thus leading to glomerular hypertension. Glomerular hypertrophy and increased glomerular pressure might be both a cause and a consequence of renal injury; understanding the renal adaptations to injury is therefore important to prevent further damage. In this Review, we discuss the current concepts of glomerular hyperfiltration and the renal hemodynamic changes associated with this condition. A physiological state of glomerular hyperfiltration occurs during pregnancy and after consumption of high-protein meals. The various diseases that have been associated with glomerular hyperfiltration, either per nephron or per total kidney, include diabetes mellitus, polycystic kidney disease, secondary focal segmental glomerulosclerosis caused by a reduction in renal mass, sickle cell anemia, high altitude renal syndrome and obesity. A better understanding of the mechanisms involved in glomerular hyperfiltration could enable the development of new strategies to prevent progression of kidney disease.

Developments in the management of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent life- threatening, hereditary disease. ADPKD is more common than sickle cell anemia, cystic fibrosis, muscular dystrophy, hemophilia, Down's syndrome, and Huntington's disease combined. ADPKD is a multisystemic disorder characterized by the progressive development of renal cysts and marked renal enlargement. Structural and functional renal deterioration occurs in ADPKD patients and is the fourth leading cause of end-stage renal disease (ESRD) in adults. Aside from the renal manifestations, extrarenal structural abnormalities, such as liver cysts, cardiovascular abnormalities, and intracranial aneurysms may lead to morbidity and mortality. Recent studies have identified prognostic factors for progressive renal impairment including gender, race, age, proteinuria, hematuria, hypertension and increased left ventricular mass index (LVMI). Early diagnosis and better understanding of the pathophysiology of the disease provides the opportunity to aggressivly treat hypertension with renin-angiotensin-aldosterone system inhibitors and thereby potentially reduce LVMI, prevent cardiovascular morbidity and mortality and slow progression of the renal disease.

Potential pharmacological interventions in polycystic kidney disease

Polycystic kidney diseases (autosomal dominant and autosomal recessive) are progressive renal tubular cystic diseases, which are characterised by cyst expansion and loss of normal kidney structure and function. Autosomal dominant polycystic kidney disease (ADPKD) is the most common life- threatening, hereditary disease. ADPKD is more prevalent than Huntington's disease, haemophilia, sickle cell disease, cystic fibrosis, myotonic dystrophy and Down's syndrome combined. Early diagnosis and treatment of hypertension with inhibitors of the renin-angiotensin-aldosterone system (RAAS) and its potential protective effect on left ventricular hypertrophy has been one of the major therapeutic goals to decrease cardiac complications and contribute to improved prognosis of the disease. Advances in the understanding of the genetics, molecular biology and pathophysiology of the disease are likely to facilitate the improvement of treatments for these diseases. Developments in describing the role of intracellular calcium ([Ca(2+)](i)) and its correlation with cellular signalling systems, Ras/Raf/mitogen extracellular kinase (MEK)/extracellular signal-regulated protein kinase (ERK), and interaction of these pathways with cyclic adenosine monophosphate (cAMP) levels, provide new insights on treatment strategies. Blocking the vasopressin V(2) receptor, a major adenylyl cyclase agonist, demonstrated significant improvements in inhibiting cytogenesis in animal models. Because of activation of the mammalian target of rapamycin (mTOR) pathway, the use of sirolimus (rapamycin) an mTOR inhibitor, markedly reduced cyst formation and decreased polycystic kidney size in several animal models. Caspase inhibitors have been shown to decrease cytogenesis and renal failure in rats with cystic disease. Cystic fluid secretion results in cyst enlargement and somatostatin analogues have been shown to decrease renal cyst progression in patients with ADPKD. The safety and efficacy of these classes of drugs provide potential interventions for experimental and clinical trials.