Sites of glandular kallikrein gene expression in fetal mice

Development biology of the renal kallikrein-kinin system

Kinins are endothelium-dependent vasodilators and natriuretic paracrine peptides that participate in the regulation of blood pressure, renal hemodynamics and sodium excretion. Several lines of evidence suggest an important role for intrarenal kinins and their receptors in kidney growth and development. (1) The developing rat kidney expresses all the components of the tissue kallikrein-kinin system: tissue kallikrein, low molecular weight (LMW) kininogen, kininase II and kinin receptors. Also, the developing liver expresses high molecular weight and LMW kininogens. Thus, a complete kinin-generating system exists in the developing kidney. (2) Gene transcription, mRNA and protein abundance, and enzymatic activity of renal kallikrein are all markedly up-regulated during postnatal kidney growth, and a positive correlation exists between renal kallikrein synthesis and the maturational rise in renal blood flow. (3) Rat glomerular mesangial cells in culture express the kinin receptors and proliferate in response to bradykinin, suggesting that endogenous kinins and their receptors modulate glomerular growth. (4) The newborn period is characterized by an activation of kinin receptor gene expression, and chronic pharmacological blockade of kinin receptors suppresses DNA synthesis in the developing but not adult kidney. Collectively, these data provide the basis for the hypothesis that endogenous kinins and the kinin receptors play an important role in the developmental biology of the metanephric kidney.

Molecular aspects of kallikrein and kininogen in the maturing kidney

Kinins are vasoactive paracrine peptides which participate in a wide range of functions, including the regulation of local organ blood flow, systemic blood pressure, transepithelial water and electrolyte transport, cellular growth, capillary permeability and inflammatory response, and pain. The recent introduction of specific bradykinin receptor subtype antagonists has greatly advanced our understanding of the role of the kallikrein-kinin system (KKS) in various physiological and disease states. However, a major gap remains in our knowledge of the role of kinins in early development. In this review, evidence is presented that the developing nephron expresses both tissue kallikrein and kininogen, and that the genes encoding the components of the KKS are subject to considerable developmental regulation. The activity of the intrarenal kinin-generating system is lowest in the developing kidney and increases with age. Completion of nephrogenesis is characterized by a marked surge in intrarenal kallikrein synthesis and gene transcription. Maturation is associated with redistribution of intrarenal kallikrein and its messenger RNA from the inner to outer cortical nephrons following the centrifugal pattern of nephron development. Challenges for the future include delineation of the direct role of kinins in the maturation of renal functions and elucidation of the molecular mechanisms underlying the developmental expression of the KKS.