Molecular Crowding: Physiologic Sensing and Control

Previous studies reported that there is an association between abnormal body fluid balance and prognosis in colitis patients. However, it remains to be clarified the effects of colitis on characteristics of body electrolytes or water content, including alternation in blood pressure. In this study, we examined the effects of colon injury on body water balance and blood pressure in the dextran sodium sulfate (DSS)-induced colitis mouse model. We evaluated body electrolytes and water content, blood pressure, and urea-associated water conservation in DSS mice. By 5 days after the treatment, DSS mice exhibited diarrhea but relatively maintained body weight and total body sodium, potassium, and water content by increases in water intake and hepatic ureagenesis. On 7 days after DSS treatment, when colitis becomes severe, DSS mice significantly decreased food and water intake, and body weight but significantly increased relative total body sodium, potassium, and water content per dry mass. Notably, DSS induced more total body dry mass loss relative to water loss. These body electrolytes and water accumulation on day 7 were associated with a reduction in urinary osmole excretion and urine volume accompanied by renal urea accumulation. DSS mice significantly increased blood pressure by day 5 and then decreased on day 7. These findings suggest that body electrolyte and fluid imbalance and alternations in blood pressure in colitis vary with the stage and severity of the condition. Assessment and correction of electrolyte and water content at the tissue level would be important to improve the prognosis of colitis.

BackgroundThe skin of the preterm infant is immature at birth and unable to serve as an effective epidermal barrier whose major functions and prevention of transepidermal water loss (TEWL).The Aimof...

Cortical collecting duct (CCD) principal cells fine tune total body salt and water balance. Part of this regulation is via intracellular Ca2+; in particular, intracellular Ca2+ regulates renal epithelial sodium channels (ENaC). We have shown that mitochondria in principal cells sequester intracellular Ca2+ to form microdomains within cells with different Ca2+ concentrations in different areas of the cell, thereby allowing differential regulation of ENaC in different parts of the cell. Failure to establish the microdomains produces disorders of Ca2+ signaling including hypertension and polycystic kidney disease. Therefore, determining how mitochondria take up Ca2+ to form these domains is crucial to understanding pathophysiology. Mitochondria in CCD principal cells interact with the ER via voltage‐dependent anion channel 1 (VDAC1) on the outer mitochondrial membrane and IP3 receptor subtype 3 (IP3RIII) on the ER membrane to form a signaling complex known as mitochondrial‐associated ER membranes (MAMs). We hypothesize that MAMs are important for mitochondrial Ca2+ sequestration by allowing the rapid release of Ca2+ from ER into the cytosol to produce a local increase in intracellular Ca2+. At the same time the MAM complex activates mitochondrial VDAC1 to take up Ca2+ and prevent a persistent or global increase in Ca2+. Subsequently, mitochondria slowly return sequestered Ca2+ to the ER to restore ER Ca2+ stores. To determine whether the absence of VDAC1 disrupts MAMs, we perfused the kidneys of VDAC1 knockout mice and their littermate wild‐type mice with glutaraldehyde. TEM imaging indicates that although MAMs in the CCD principal cells were intact in both VDAC1 knockout and wild type mice, the mitochondria of the VDAC1 knockouts were larger than those of their wild‐type counterparts. To examine whether MAMs affect Ca2+ signaling domains, we imaged mpkCCD cells (n = 5) transfected with green Lck‐GCaMP2 (AddGene), a membrane‐associated Ca2+ sensor, and treated the cells with MDIVI‐1, an agent that selectively inhibits MAMs by blocking the dynamin‐dependent processes required for MAM formation. We applied UTP apically to increase intracellular Ca2+ beneath the apical membrane and found that Ca2+ increased strongly near the apical membrane, but only weakly in other parts of the cell. In cells treated with MDIVI‐1, Ca2+ increased less but was more uniformly distributed in all parts of the cell. To test whether VDAC1 influences ENaC activity in vivo, since ENaC currents increase as intracellular Ca2+ decreases, we examined ENaC regulation in renal tubules from VDAC1 knockout mice compared to wildtype mice on diets with different amounts of salt. We dissected and split open the cortical collecting duct, and then applied single‐channel patch clamp to the CCD principal cells. The activity of ENaC in wildtype mice decreased with increased sodium in the diet. ENaC activity in VDAC1 was significantly higher than wild type mice and activity did not depend upon dietary sodium. We conclude that inhibition of the associations between mitochondria and ER interferes with local Ca2+ signaling and therefore disrupts the ability of Ca2+ to regulate ENaC.Support or Funding InformationSupported by APS UGSRF and Emory's Robert P. Apkarian Integrated Electron Microscopy Core. VDAC1 knockout mice were obtained from Dr. William Craigen at Baylor University.

the timing of physiological events is carefully controlled so that incompatible processes do not compete and complementary functions coincide. Given the pivotal role of the hypothalamus in homeostatic regulation, the discovery that a master circadian pacemaker resides in this region was not

High density of intracellular macromolecules creates a special condition known as macromolecular crowding (MC). One well-established consequence of MC is that only a slight change in the concentration of macromolecules (e.g., proteins) results in a shift of chemical equilibria towards the formation of macromolecular complexes and oligomers. This suggests a physiological mechanism of converting cell density changes into cellular responses. In this review, we start by providing a general overview of MC; then we examine the available experimental evidence that MC may act as a direct signaling factor in several types of cellular activities: mechano- and osmosensing, cell volume recovery in anisosmotic solutions, and apoptotic shrinkage. The latter phenomenon is analyzed in particular detail, as persistent shrinkage is known both to cause apoptosis and to occur during apoptosis resulting from other stimuli. We point to specific apoptotic reactions that involve formation of macromolecular complexes and, therefore, may provide a link between shrinkage and downstream responses.

The soluble prorenin receptor (sPRR) plays an important role in fluid and electrolyte balance. In rodent models, sPRR contributes to aquaporin2(AQP2)-dependent antidiuretic action. However, there is a gap of knowledge concerning the functional role of locally produced human sPRR from the kidney. Hence, we evaluated the role of renal-derived human sPRR in fluid and electrolyte homeostasis.Human sPRR-Myc-tag transgenic mice were bred with mice expressing Hoxb7/Cre to selectively express human sPRR in the collecting duct (RHsPRR). RHsPRR and control (CTL) male and female mice were fed a standard diet for 10 months (n=8-11/group). Body weight was examined weekly, body composition monthly and water balance at study endpoint. Western blot analysis depicted the presence of human sPRR-Myc-tag (28 KDa) in the cortex and medulla of RHsPRR male and female mice validating the humanized mouse model.Renal-derived human sPRR did not change body weight in male or female mice (Male: CTL: 34±1, RHsPRR: 33±1 g; Female: CTL: 28±1, RHsPRR: 30±1 g) nor kidney function assessed by GFR (Male: CTL: 817±83, RHsPRR: 1088±163 μl/min/100gBW; Female: CTL: 1057±75, RHsPRR: 875±89 μl/min/100gBW). In male mice, renal-derived human sPRR significantly elevated plasma sodium (Male: CTL: 115±4, RHsPRR: 127±3 mmol/L; P<0.05) and ENaC gene expression (M: 1.7±0.7 and 3.7±0.9 2 -ΔΔCT , P<0.05). Urine flow rate was decreased (Male: CTL: 1.0±0.2, RHsPRR: 0.6±0.2 ml; P<0.05) and AQP2 protein expression was increased in male RHsPRR mice compared to CTL (M: 0.13±0.05 and 0.44±0.12 AU, P<0.05), suggesting that renal-derived human sPRR elicits hypernatremia by stimulating sodium reabsorption via ENaC-dependent mechanism and water reabsorption by AQP2 expression.In female mice, renal-derived human sPRR did not change plasma sodium (Female: CTL: 120±7, RHsPRR: 118±5 mmol/L), ENaC gene expression (F: 1.2±0.2 and 1.4±0.1 2 -ΔΔCT ), urine flow rate (Female: CTL: 0.4±0.1, RHsPRR: 0.5±0.1 ml) or AQP2 protein expression (F: 0.20±0.03 and 0.20±0.06 AU, P<0.05).Our data suggest that renal cortical and medullary human sPRR regulates water and electrolyte balance in a sex specific-manner. Translationally, human sPRR could be a promising therapeutic target to treat hypernatremia in men.

Bioaccessibility mechanisms, fortification strategies, processing impact on bioavailability, and therapeutic potentials of minerals in cereals

To give a causal explanation of an event is to show how that event could be deduced from a set of universal laws and a set of initial conditions. How can this philosophical definition be related to the diagnostic causal explanations of a practicing expert? An expert physician gives a causal explanation of a disease state by referring to knowledge of the structure of the physiological mechanisms involved (the laws) and to the environment that the mechanism is exposed to (the initial state). The expert's knowledge, however, is qualitative and is thus able to express incomplete knowledge about the exact structure of the mechanism or the precise state of the patient. A qualitative representation for the structure of a mechanism, as well as the QSIM algorithm for deriving qualitative behavioral predictions from that structure and an initial state, are described. Looking in detail at the mechanism whereby the kidney maintains the body's water balance, qualitative predictions are demonstrated of 1) the response of the normal mechanism to a change in its environment, 2) the response of the diseased mechanism to the normal environment, and 3) the response of the diseased mechanism to therapy. To extend these methods to more complex problems, methods are required to abstract a complex mechanism into a hierarchy of simpler models. An abstraction relation based on relative time scales is presented which allows one equilibrium process in a complex system to view faster processes as instantaneous and slower processes as constant.

The effect of salt intake on the hypertensive response to long-term infusion of endothelin-1 was investigated. Chronically instrumented male Sprague-Dawley rats (325-375 g) were used in a 15-day protocol that included 3 control days followed by 7 days of endothelin-1 infusion at 5.0 pmol.kg-1.min-1 and 5 days of recovery. Rats were maintained on either a normal sodium chloride intake (2.0 meq Na+ per day; normal sodium) or a high sodium chloride intake (6.0 meq Na+ per day; high sodium) throughout the protocol. Control rats received normal or high sodium intakes but not endothelin-1. In high-sodium rats, endothelin-1 produced a significant increase in mean arterial pressure and total peripheral resistance; a significant bradycardia was observed only on the first day after the start of the endothelin-1 infusion. Cardiac output, stroke volume, water balance, and urinary sodium and potassium excretion remained unchanged. Termination of endothelin-1 infusion resulted in rapid normalization of both arterial pressure and peripheral resistance. In contrast, normal sodium rats exhibited no alteration in mean arterial pressure, heart rate, total peripheral resistance, stroke volume, water balance, or urinary sodium and potassium excretion throughout the endothelin-1 infusion protocol. The hypertension produced by endothelin-1 infusion cannot be explained by alterations in salt or water balance since endothelin-1 infusion in high sodium animals produced significant increases in mean arterial pressure with no observable changes in water or electrolyte balance. These results indicate that endothelin-induced hypertension in conscious rats is a salt-dependent model of hypertension.

Diffusion NMR studies of macromolecular complex formation, crowding and confinement in soft materials

The human body is two-thirds water. The ability of ensuring the proper amount of water inside the body is essential for the survival of mammals. The key event for maintenance of body water balance is water reabsorption in the kidney collecting ducts, which is regulated by aquaporin-2 (AQP2). AQP2 is a channel that is exclusively selective for water molecules and never allows permeation of ions or other small molecules. Under normal conditions, AQP2 is restricted within the cytoplasm of the collecting duct cells. However, when the body is dehydrated and needs to retain water, AQP2 relocates to the apical membrane, allowing water reabsorption from the urinary tubule into the cell. Its impairments result in various water balance disorders including diabetes insipidus, which is a disease characterized by a massive loss of water through the kidney, leading to severe dehydration in the body. Dysregulation of AQP2 is also a common cause of water retention and hyponatremia that exacerbate the prognosis of congestive heart failure and hepatic cirrhosis. Many studies have uncovered the regulation mechanisms of AQP2 at the single-molecule level, the whole-body level, and the clinical level. In clinical practice, urinary AQP2 is a useful marker for body water balance (hydration status). Moreover, AQP2 is now attracting considerable attention as a potential therapeutic target for water balance disorders which commonly occur in many diseases.

Bioelectrical impedance analysis has found extensive application as a simple non-invasive method for the assessment of body fluid volumes. The measured impedance is, however, not only related to the volume of fluid but also to its inherent resistivity. The primary determinant of the resistivities of body fluids is the concentration of ions. The aim of this study was to investigate the sensitivity of bioelectrical impedance analysis to bodily ion status. Whole body impedance over a range of frequencies (4-1012 kHz) of rats was measured during infusion of various concentrations of saline into rats concomitant with measurement of total body and intracellular water by tracer dilution techniques. Extracellular resistance (R0), intracellular resistance (Ri) and impedance at the characteristic frequency (Zc) were calculated. R0 and Zc were used to predict extracellular and total body water respectively using previously published formulae. The results showed that whilst R0 and Zc decreased proportionately to the amount of NaCl infused, Ri increased only slightly. Impedances at the end of infusion predicted increases in TBW and ECW of approximately 4-6% despite a volume increase of less than 0.5% in TBW due to the volume of fluid infused. These data are discussed in relation to the assumption of constant resistivity in the prediction of fluid volumes from impedance data.

EDITORIAL article Front. Endocrinol., 18 May 2016Sec. Neuroendocrine Science Volume 7 - 2016 | https://doi.org/10.3389/fendo.2016.00041

Extracellular and interstitial fluid volume in obesity with and without associated systemic hypertension

The cytoplasm is a crowded, visco-elastic environment whose physical properties change according to physiological or developmental states. How the physical properties of the cytoplasm impact cellular functions invivo remains poorly understood. Here, we probe the effects of cytoplasmic concentration on microtubules by applying osmotic shifts to fission yeast, moss, and mammalian cells. We show that the rates of both microtubule polymerization and depolymerization scale linearly and inversely with cytoplasmic concentration; an increase in cytoplasmic concentration decreases the rates of microtubule polymerization and depolymerization proportionally, whereas a decrease in cytoplasmic concentration leads to the opposite. Numerous lines of evidence indicate that these effects are due to changes in cytoplasmic viscosity rather than cellular stress responses or macromolecular crowding per se. We reconstituted these effects on microtubules invitro by tuning viscosity. Our findings indicate that, even in normal conditions, the viscosity of the cytoplasm modulates the reactions that underlie microtubule dynamic behaviors.