A new view of macula densa cell microanatomy

Although macula densa (MD) cells are chief regulatory cells in the nephron with unique microanatomical features, they have been difficult to study in full detail due to their inaccessibility and limitations in earlier microscopy techniques. The present study used a new mouse model with a comprehensive imaging approach to visualize so far unexplored microanatomical features of MD cells, their regulation, and functional relevance. MD-GFP mice with conditional and partial induction of green fluorescent protein (GFP) expression, which specifically and intensely illuminated only single MD cells, were used with fluorescence microscopy of fixed tissue and live MD cells in vitro and in vivo with complementary electron microscopy of the rat, rabbit, and human kidney. An elaborate network of major and minor cell processes, here named maculapodia, were found at the cell base, projecting toward other MD cells and the glomerular vascular pole. The extent of maculapodia showed upregulation by low dietary salt intake and the female sex. Time-lapse imaging of maculapodia revealed highly dynamic features including rapid outgrowth and an extensive vesicular transport system. Electron microscopy of rat, rabbit, and human kidneys and three-dimensional volume reconstruction in optically cleared whole-mount MD-GFP mouse kidneys further confirmed the presence and projections of maculapodia into the extraglomerular mesangium and afferent and efferent arterioles. The newly identified dynamic and secretory features of MD cells suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD cells and between MD and other target cells.NEW & NOTEWORTHY This study illuminated a physiologically regulated dense network of basal cell major and minor processes (maculapodia) in macula densa (MD) cells. The newly identified dynamic and secretory features of these microanatomical structures suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD and other target cells. Detailed characterization of the function and molecular details of MD cell intercellular communications and their role in physiology and disease warrant further studies

Intravital imaging of podocyte calcium in glomerular injury and disease

Intracellular calcium ([Ca-2i](i)) signaling mediates physiological and pathological processes in multiple organs, including the renal podocyte; however, in vivo podocyte [Ca-2i](i) dynamics are not fully understood. Here we developed an imaging approach that uses multiphoton microscopy (MPM) to directly visualize podocyte [Ca-2i](i) dynamics within the intact kidneys of live mice expressing a fluorescent calcium indicator only in these cells. [Ca-2i](i) was at a low steady-state level in control podocytes, while Ang II infusion caused a minor elevation. Experimental focal podocyte injury triggered a robust and sustained elevation of podocyte [Ca-2i](i) around the injury site and promoted cell-to-cell propagating podocyte [Ca-2i](i) waves along capillary loops. [Ca-2i](i) wave propagation was ameliorated by inhibitors of purinergic [Ca-2i](i) signaling as well as in animals lacking the P2Y2 purinergic receptor. Increased podocyte [Ca-2i](i) resulted in contraction of the glomerular tuft and increased capillary albumin permeability. In preclinical models of renal fibrosis and glomerulosclerosis, high poclocyte [Ca-2i](i) correlated with increased cell motility. Our fmdings provide a visual demonstration of the in vivo importance of pod.ocyte [Ca-2i](i) in glomerular pathology and suggest that purinergic [Ca-2i](i) signaling is a robust and key pathogenic mechanism in pod.ocyte injury. This in vivo imaging approach will allow future detailed investigation of the molecular and cellular mechanisms of glomerular disease in the intact living kidney

Intravital imaging of podocyte calcium in glomerular injury and disease

Intracellular calcium ([Ca(2+)](i)) signaling mediates physiological and pathological processes in multiple organs, including the renal podocyte; however, in vivo podocyte [Ca(2+)](i) dynamics are not fully understood. Here we developed an imaging approach that uses multiphoton microscopy (MPM) to directly visualize podocyte [Ca(2+)](i) dynamics within the intact kidneys of live mice expressing a fluorescent calcium indicator only in these cells. [Ca(2+)](i) was at a low steady-state level in control podocytes, while Ang II infusion caused a minor elevation. Experimental focal podocyte injury triggered a robust and sustained elevation of podocyte [Ca(2+)](i) around the injury site and promoted cell-to-cell propagating podocyte [Ca(2+)](i) waves along capillary loops. [Ca(2+)](i) wave propagation was ameliorated by inhibitors of purinergic [Ca(2+)](i) signaling as well as in animals lacking the P2Y2 purinergic receptor. Increased podocyte [Ca(2+)](i) resulted in contraction of the glomerular tuft and increased capillary albumin permeability. In preclinical models of renal fibrosis and glomerulosclerosis, high podocyte [Ca(2+)](i) correlated with increased cell motility. Our findings provide a visual demonstration of the in vivo importance of podocyte [Ca(2+)](i) in glomerular pathology and suggest that purinergic [Ca(2+)](i) signaling is a robust and key pathogenic mechanism in podocyte injury. This in vivo imaging approach will allow future detailed investigation of the molecular and cellular mechanisms of glomerular disease in the intact living kidney

Essential role and therapeutic targeting of the glomerular endothelial glycocalyx in lupus nephritis

Lupus nephritis (LN) is a major organ complication and cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). There is an unmet medical need for developing more efficient and specific, mechanism-based therapies, which depends on improved understanding of the underlying LN pathogenesis. Here we present direct visual evidence from high-power intravital imaging of the local kidney tissue microenvironment in mouse models showing that activated memory T cells originated in immune organs and the LN-specific robust accumulation of the glomerular endothelial glycocalyx played central roles in LN development. The glomerular homing of T cells was mediated via the direct binding of their CD44 to the hyaluronic acid (HA) component of the endothelial glycocalyx, and glycocalyx-degrading enzymes efficiently disrupted homing. Short-course treatment with either hyaluronidase or heparinase III provided long-term organ protection as evidenced by vastly improved albuminuria and survival rate. This glycocalyx/HA/memory T cell interaction is present in multiple SLE-affected organs and may be therapeutically targeted for SLE complications, including LN

The absence of intrarenal ACE protects against hypertension

10.1172/JCI65460Journal of Clinical Investigation12352011-202