Effects of biomechanical forces on signaling in the cortical collecting duct (CCD)

Abstract

An increase in tubular fluid flow rate (TFF) stimulates Na reabsorption and K secretion in the cortical collecting duct (CCD) and subjects cells therein to biomechanical forces including fluid shear stress (FSS) and circumferential stretch (CS). Intracellular MAPK and extracellular autocrine/paracrine PGE2 signaling regulate cation transport in the CCD and, at least in other systems, are affected by biomechanical forces. We hypothesized that FSS and CS differentially affect MAPK signaling and PGE2 release to modulate cation transport in the CCD. To validate that CS is a physiological force in vivo, we applied the intravital microscopic approach to rodent kidneys in vivo to show that saline or furosemide injection led to a 46.5 ± 2.0 or 170 ± 32% increase, respectively, in distal tubular diameter. Next, murine CCD (mpkCCD) cells were grown on glass or silicone coated with collagen type IV and subjected to 0 or 0.4 dyne/cm2 of FSS or 10% CS, respectively, forces chosen based on prior biomechanical modeling of ex vivo microperfused CCDs. Cells exposed to FSS expressed an approximately twofold greater abundance of phospho(p)-ERK and p-p38 vs. static cells, while CS did not alter p-p38 and p-ERK expression compared with unstretched controls. FSS induced whereas CS reduced PGE2 release by ∼40%. In conclusion, FSS and CS differentially affect ERK and p38 activation and PGE2 release in a cell culture model of the CD. We speculate that TFF differentially regulates biomechanical signaling and, in turn, cation transport in the CCD.

Primary cilia‐regulated transcriptome in the renal collecting duct

“…The urinary flow rate is highly variable (5-15 nl/min under physiologic conditions) depending on heart rate and a tubuloglomerular feedback mechanism mediated by the macula densa (3,4). Variation of urinary flow can also occur secondary to volume expansion, osmotic diuresis, or diuretic administration (5,6). Fluctuations in urinary flow result in changes in luminal pressure, which cause axial fluid shear stress and circumferential stretch.…”

Hyperfiltration-associated biomechanical forces in glomerular injury and response: Potential role for eicosanoids

“…Increased flow in cortical collecting duct results in greater sodium reabsorption and potassium secretion into urine. Circumferential stretch applied to cortical collecting duct decreases PGE 2 release while FFSS increases PGE 2 [85,86]. FFSS but not stretch upregulates COX-2, neutral sphingomyelinase, endothelin, phospho-ERK and phospho-p38 in cortical collecting duct cells [85–89].…”

Surgical preparation of rats and mice for intravital microscopic imaging of abdominal organs

“…Isoflurane is an inhalational agent that is most valuable in rats that have compromised physiologic states due to disease models employed [14, 15, 16, 17]. Use of Isoflurane does require a closed anesthesia circuit with a pressurized vaporizer, metered oxygen flow, and utilizing a gas waste scavenging system.…”

“…Because of anatomical location of these organs and the fact that many of them have long vascular pedicles that allow considerable mobility, need to two types of incisions are utilized to expose the organs of interest: 1) left flank vertical incision and 2) midline horizontal incision. Many investigators select the inverted microscope as the optimal scope for imaging the intra-abdominal organs that we study [1, 5, 6, 9, 10, 12, 13, 14, 16, 17, 18, 19, 24, 25, 26, 27, 28, 29]. …”

“…The dish is directly mounted into the microscope stage such that the organ can be imaged from below. Oriented in this way, the animal’s weight serves to hold the organ in place in the dish, minimizing respiratory and circulatory motion artifacts [1, 5, 6, 9, 10, 12, 13, 14, 16, 17, 18, 19, 24, 25, 26, 27, 28, 29]. This approach also requires surgical procedures that are simpler, faster, and less invasive than those needed to immobilize an organ for imaging on an upright system [1].…”