Biology subjects

Satlin, L. M.

Publications and source records attributed to Satlin, L. M..

4 recordsLinked to original sources

bioRxiv2025

Perfusable 3D models of ureteric bud and collecting duct tubules

Recent protocols have emerged to derive ureteric bud (UB) and collecting duct (CD) organoids directly from human induced pluripotent stem cells (hiPSCs). However, these 3D kidney tissues lack biophysical cues from luminal flow and a drainage outlet. To address these limitations, we have created perfusable 3D models of UB and CD tubules. UB organoids are first generated from hiPSCs followed by their dissociation into individual UB cells. Individual UB cells are then seeded onto a 3D perfusable channel embedded within an extracellular matrix composed of fragmented basement membrane matrix and collagen I, where they self-assemble into a confluent monolayer. During in vitro perfusion, these cells exhibit UB-like marker expression over several weeks, during which they undergo budding akin to early branching morphogenesis in developing kidneys. To further promote network formation, UB cells are bioprinted adjacent to a perfusable UB tubule, which form interconnections through luminal fusion. Finally, these 3D perfusable UB tubules are differentiated into collecting duct tubules under luminal flow. Our platform facilitates fundamental understanding of human collecting duct formation during renal development, while paving the way for using these physiologically relevant models for drug testing, disease modeling, and, ultimately, integration into bioprinted kidney tissues for therapeutic use.

bioengineering↗

bioRxiv2024

Proteolytic Cleavage of the ENaC gamma Subunit: Impact Upon Na+ and K+ Handling

The ENaC gamma subunit is essential for homeostasis of Na+, K+, and body fluid. Dual subunit cleavage before and after a short inhibitory tract allows dissociation of this tract, increasing channel open probability (PO), in vitro. Cleavage proximal to the tract occurs at a furin recognition sequence (143RKRR146 in mouse). Loss of furin-mediated cleavage prevents in vitro activation of the channel by proteolysis at distal sites. We hypothesized that 143RKRR146 mutation to 143QQQQ146 (Q4) in 129/Sv mice would reduce ENaC PO, impair flow-stimulated flux of Na+ (JNa) and K+ (JK) in perfused collecting ducts, reduce colonic amiloride-sensitive short circuit current (ISC), and impair Na+, K+, and body fluid homeostasis. Immunoblot of Q4/Q4 mouse kidney lysates confirmed loss of a band consistent in size with the furin-cleaved proteolytic fragment. However, Q4/Q4 male mice on a low Na+ diet did not exhibit altered ENaC PO or flow-induced JNa, though flow-induced JK modestly decreased. Colonic amiloride-sensitive ISC in Q4/Q4 mice was not altered. Q4/Q4 males, but not females, exhibited mildly impaired fluid volume conservation when challenged with a low Na+ diet. Blood Na+ and K+ were unchanged on a regular, low Na+, or high K+ diet. These findings suggest that biochemical evidence of gamma subunit cleavage should not be used in isolation to evaluate ENaC activity. Further, factors independent of gamma subunit cleavage modulate channel PO and the influence of ENaC on Na+, K+, and fluid volume homeostasis in 129/Sv mice, in vivo.

physiology↗

bioRxiv2023

Mineralocorticoid receptor-independent activation of ENaC in bile duct ligated mice

Sodium and fluid retention in liver disease is classically thought to result from reduced effective circulating volume and stimulation of the renin-angiotensin-aldosterone system (RAAS). Aldosterone dives Na+ retention by activating the mineralocorticoid receptor and promoting the maturation and apical surface expression of the epithelial Na+ channel (ENaC), found in the aldosterone-sensitive distal nephron. However, evidence of fluid retention without RAAS activation suggests the involvement of additional mechanisms. Liver disease can greatly increase plasma and urinary bile acid concentrations and have been shown to activate ENaC in vitro. We hypothesize that elevated bile acids in liver disease activate ENaC and drive fluid retention independent of RAAS. We therefore increased circulating bile acids in mice through bile duct ligation (BDL) and measured effects on urine and body composition, while using spironolactone to antagonize the mineralocorticoid receptor. We found BDL lowered blood [K+] and hematocrit, and increased benzamil-sensitive natriuresis compared to sham, consistent with ENaC activation. BDL mice also gained significantly more body water. Blocking ENaC reversed fluid gains in BDL mice but had no effect in shams. In isolated collecting ducts from rabbits, taurocholic acid stimulated net Na+ absorption but had no effect on K+ secretion or flow-dependent ion fluxes. Our results provide experimental evidence for a novel aldosterone-independent mechanism for sodium and fluid retention in liver disease which may provide additional therapeutic options for liver disease patients. SignificanceAdvanced liver disease is often complicated by renal sodium retention, leading to fluid retention, poor outcomes, and increased mortality. This is currently thought to be driven by increased levels of the hormone aldosterone, although numerous published reports demonstrate normal aldosterone levels in many liver patients with volume overload. Management of these patients relies on diuretics and Na+ restriction, or more invasive procedures with increased risks for diuretic-resistant patients. Here, we report a novel mechanism for fluid retention in liver disease, which provides a basis to develop new strategies to treat fluid retention in these patients.

physiology↗

bioRxiv2021

L-WNK1 is required for BK channel activation in intercalated cells

BK channels expressed in intercalated cells (ICs) in the aldosterone-sensitive distal nephron (ASDN) mediate flow-induced K+ secretion. In the ASDN of mice and rabbits, IC BK channel expression and activity increase with a high K+ diet. In cell culture, the long isoform of the kinase WNK1 (L-WNK1) increases BK channel expression and activity. Apical L-WNK1 expression is selectively enhanced in ICs in the ASDN of rabbits on a high K+ diet, suggesting that L-WNK1 contributes to BK channel regulation by dietary K+. We examined the role of IC L-WNK1 expression in enhancing BK channel activity in response to a high K+ diet. Mice with an IC-selective deletion of L-WNK1 (IC-L-WNK1-KO) and littermate control mice were placed on a high K+ (5% K+ as KCl) diet for at least 10 days. IC-L-WNK1-KO mice exhibited higher blood K+ concentrations ([K+]) than controls. BK channel-dependent whole-cell currents in ICs from cortical collecting ducts of high K+ fed IC-L-WNK1-KO mice were reduced compared to controls. Six-hour urinary K+ excretion in response a saline load was similar in IC-L-WNK1-KO mice and controls. The observations that IC-L-WNK1-KO mice have higher blood [K+] and reduced IC BK channel currents are consistent with impaired urinary K+ secretion, and suggest that IC L-WNK1 has a role in the renal adaptation to a high K+ diet.

physiology↗