Flexible and multifaceted: the plasticity of renin-expressing cells

Hold the salt for kidney regeneration

The macula densa (MD) is a distinct cluster of approximately 20 specialized kidney epithelial cells that constitute a key component of the juxtaglomerular apparatus. Unlike other renal tubular epithelial cell populations with functions relating to reclamation or secretion of electrolytes and solutes, the MD acts as a cell sensor, exerting homeostatic actions in response to sodium and chloride changes within the tubular fluid. Electrolyte flux through apical sodium transporters in MD cells triggers release of paracrine mediators, affecting blood pressure and glomerular hemodynamics. In this issue of the JCI, Gyarmati and authors explored a program of MD that resulted in activation of regeneration pathways. Notably, regeneration was triggered by feeding mice a low-salt diet. Furthermore, the MD cells showed neuron-like properties that may contribute to their regulation of glomerular structure and function. These findings suggest that dietary sodium restriction and/or targeting MD signaling might attenuate glomerular injury.

Neuropilin-1 regulates renin synthesis in juxtaglomerular cells

Renin is the key enzyme of the systemic renin-angiotensin-aldosterone system, which plays an essential role in regulating blood pressure and maintaining electrolyte and extracellular volume homeostasis. Renin is mainly produced and secreted by specialized juxtaglomerular (JG) cells in the kidney. In the present study, we report for the first time that the conserved transmembrane receptor neuropilin-1 (NRP1) participates in the development of JG cells and plays a key role in renin production. We used the myelin protein zero-Cre (P0-Cre) to abrogate Nrp1 constitutively in P0-Cre lineage-labelled cells of the kidney. We found that the P0-Cre precursor cells differentiate into renin-producing JG cells. We employed a lineage-tracing strategy combined with RNAscope quantification and metabolic studies to reveal a cell-autonomous role for NRP1 in JG cell function. Nrp1-deficient animals displayed abnormal levels of tissue renin expression and failed to adapt properly to a homeostatic challenge to sodium balance. These findings provide new insights into cell fate decisions and cellular plasticity operating in P0-Cre-expressing precursors and identify NRP1 as a novel key regulator of JG cell maturation. KEY POINTS: Renin is a centrepiece of the renin-angiotensin-aldosterone system and is produced by specialized juxtaglomerular cells (JG) of the kidney. Neuropilin-1 (NRP1) is a conserved membrane-bound receptor that regulates vascular and neuronal development, cancer aggressiveness and fibrosis progression. We used conditional mutagenesis and lineage tracing to show that NRP1 is expressed in JG cells where it regulates their function. Cell-specific Nrp1 knockout mice present with renin paucity in JG cells and struggle to adapt to a homeostatic challenge to sodium balance. The results support the versatility of renin-producing cells in the kidney and may open new avenues for therapeutic approaches.

Salt and Aldosterone - Reciprocal and Combined Effects in Preclinical Models and Humans

Primary aldosteronism is an endocrine disorder caused by excessive production of aldosterone by the adrenal glands, and is recognized as the most important cause of endocrine hypertension. With specific therapy, this type of hypertension is potentially curable. In the general population, high salt intake increases the risk for cardiovascular diseases like stroke. In populations with aldosterone excess, observational and experimental data suggest that aldosterone-induced organ damage requires a combination of high dietary salt intake and high plasma aldosterone, i.e., plasma aldosterone levels inappropriately high for salt status. Therefore, understanding the relationship between plasma aldosterone levels and dietary salt intake and the nature of their combined effects is crucial for developing effective prevention and treatment strategies. In this review, we present an update on findings about primary aldosteronism and salt intake and the underlying mechanisms governing their interaction.

Connexin 40-Mediated Regulation of Systemic Circulation and Arterial Blood Pressure

Vascular system is a complex network in which different cell types and vascular segments must work in concert to regulate blood flow distribution and arterial blood pressure. Although paracrine/autocrine signaling is involved in the regulation of vasomotor tone, direct intercellular communication via gap junctions plays a central role in the control and coordination of vascular function in the microvascular network. Gap junctions are made up by connexin (Cx) proteins, and among the four Cxs expressed in the cardiovascular system (Cx37, Cx40, Cx43, and Cx45), Cx40 has emerged as a critical signaling pathway in the vessel wall. This Cx is predominantly found in the endothelium, but it is involved in the development of the cardiovascular system and in the coordination of endothelial and smooth muscle cell function along the length of the vessels. In addition, Cx40 participates in the control of vasomotor tone through the transmission of electrical signals from the endothelium to the underlying smooth muscle and in the regulation of arterial blood pressure by renin-angiotensin system in afferent arterioles. In this review, we discuss the participation of Cx40-formed channels in the development of cardiovascular system, control and coordination of vascular function, and regulation of arterial blood pressure.