Uremic cardiomyopathy, characterized by hypertension, cardiac hypertrophy, and fibrosis, is a complication of chronic kidney disease (CKD). Urea transporter (UT) inhibition increases the excretion of ...water and urea, but the effect on uremic cardiomyopathy has not been studied. We tested UT inhibition by dimethylthiourea (DMTU) in 5/6 nephrectomy mice. This treatment suppressed CKD‐induced hypertension and cardiac hypertrophy. In CKD mice, cardiac fibrosis was associated with upregulation of UT and vimentin abundance. Inhibition of UT suppressed vimentin amount. Left ventricular mass index in DMTU‐treated CKD was less compared with non‐treated CKD mice as measured by echocardiography. Nephrectomy was performed in UT‐A1/A3 knockout (UT‐KO) to further confirm our finding. UT‐A1/A3 deletion attenuates the CKD‐induced increase in cardiac fibrosis and hypertension. The amount of α‐smooth muscle actin and tgf‐β were significantly less in UT‐KO with CKD than WT/CKD mice. To study the possibility that UT inhibition could benefit heart, we measured the mRNA of renin and angiotensin‐converting enzyme (ACE), and found both were sharply increased in CKD heart; DMTU treatment and UT‐KO significantly abolished these increases. Conclusion: Inhibition of UT reduced hypertension, cardiac fibrosis, and improved heart function. These changes are accompanied by inhibition of renin and ACE.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Muscle wasting occurs in a variety of clinical situations, including denervation. There is no effective pharmacological treatment for muscle wasting. In this study, we used a tibial nerve denervation ...model to test acupuncture plus low-frequency electric stimulation (Acu-LFES) as a therapeutic strategy for muscle atrophy. Acupuncture needles were connected to an SDZ-II electronic acupuncture device delivering pulses at 20 Hz and 1 mA; the treatment was 15 min daily for 2 wk. Acu-LFES prevented soleus and plantaris muscle weight loss and increased muscle cross-sectional area in denervated mice. The abundances of Pax7, MyoD, myogenin, and embryonic myosin heavy chain were significantly increased by Acu-LFES in both normal and denervated muscle. The number of central nuclei was increased in Acu-LFES-treated muscle fibers. Phosphorylation of Akt was downregulated by denervation leading to a decline in muscle mass; however, Acu-LFES prevented the denervation-induced decline largely by upregulation of the IGF-1 signaling pathway. Acu-LFES reduced the abundance of muscle catabolic proteins forkhead O transcription factor and myostatin, contributing to the attenuated muscle atrophy. Acu-LFES stimulated the expression of macrophage markers (F4/80, IL-1b, and arginase-1) and inflammatory cytokines (IL-6, IFNγ, and TNFα) in normal and denervated muscle. Acu-LFES also stimulated production of the muscle-specific microRNAs miR-1 and miR-206. We conclude that Acu-LFES is effective in counteracting denervation-induced skeletal muscle atrophy and increasing muscle regeneration. Upregulation of IGF-1, downregulation of myostatin, and alteration of microRNAs contribute to the attenuation of muscle atrophy in denervated mice.
Chronic kidney disease (CKD) impairs muscle protein metabolism leading to muscle atrophy, and exercise can counteract this muscle wasting. Here we evaluated how resistance exercise (muscle overload) ...and endurance training (treadmill running) affect CKD-induced abnormalities in muscle protein metabolism and progenitor cell function using mouse plantaris muscle. Both exercise models blunted the increase in disease-induced muscle proteolysis and improved phosphorylation of Akt and the forkhead transcription factor FoxO1. Muscle overloading, but not treadmill running, corrected protein synthesis and levels of mediators of protein synthesis such as phosphorylated mTOR and p70S6K in the muscles of mice with CKD. In these mice, muscle overload, but not treadmill, running, increased muscle progenitor cell number and activity as measured by the amounts of MyoD, myogenin, and eMyHC mRNAs. Muscle overload not only increased plantaris weight and reduced muscle proteolysis but also corrected intracellular signals regulating protein and progenitor cell function in mice with CKD. Treadmill running corrects muscle proteolysis but not protein synthesis or progenitor cell function. Our results provide a basis for evaluating different types of exercise on muscle atrophy in patients with chronic kidney disease.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The syndrome of inappropriate antidiuretic hormone secretion (SIADH) consists of unregulated, elevated vasopressin levels and can lead to hyponatremia. Vasopressin escape is the body’s defense ...mechanism to limit hyponatremia. The sodium‐glucose transporter (SGLT‐2) inhibitor, empagliflozin, was identified as a treatment for hyponatremia; however, the mechanism of empagliflozin’s effect is unclear. This project investigates empagliflozin’s impact on vasopressin escape in rats with the hypothesis that empagliflozin accelerates escape via key transport protein alteration. Rats were implanted with vasopressin mini‐pumps to mimic SIADH. The first cohort consisted of male rats and a second cohort compared responses in female rats. On day 2, half the rats were given empagliflozin (~15 mg/kg) via diet. Rats were sacrificed on days 7 or 14. Blood and kidney tissue were collected. Total Aquaporin‐2 (AQP2), pSer‐Aquaporin‐2, and NKCC2 were analyzed by western blot. At day 7, serum sodium levels for the female rats were: empagliflozin 110.1+1.7 mmol/L vs 93.3+1.1 mmol/L for the controls (n=5, p<0.001). Serum sodium levels for the male rats were: empagliflozin 136.0+4.8 mmol/L vs 121.4+3.0 mmol/L for the controls (n=4, p<0.05). NKCC2 abundance in the empagliflozin group was 60% lower than control on day 7 (n=5, p<0.05) for female rats, and 77% lower than control in male rats (n =4, p<0.001). Because changes in the AQP2 levels were similar between the sexes, these data were combined. Total AQP2 abundance was 2.3 fold increased in the empagliflozin group on day 7 and 8 fold greater in the empagliflozin group at day 14 (n=9) compared to the control group. Both pSer256‐AQP2 and pSer261‐AQP2 were increased in the empagliflozin groups at both 7 and 14 days vs their respective control groups. pSer256‐AQP2 increased 2.1 (day 7) and 8.5 fold (day 14); pSer261‐AQP2 increased 3.2 fold (day 7) and 5.0 fold (day 14) (n=9/group). We conclude that empagliflozin accelerates vasopressin escape during SIADH primarily through a decrease in NKCC2 abundance in both male and female rats. This will hasten recovery from hyponatremia in SIADH.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The mechanisms by which aldosterone increases Na+, K+ ATPase and sodium channel activity in cortical collecting duct and distal nephron have been extensively studied. Recent investigations ...demonstrate that aldosterone increases Na–H exchanger-3 (NHE-3) activity, bicarbonate transport, and H+ ATPase in proximal tubules. However, the role of aldosterone in regulation of Na+, K+ ATPase in proximal tubules is unknown. We hypothesize that aldosterone increases Na+, K+ ATPase activity in proximal tubules through activation of the mineralocorticoid receptor (MR). Immunohistochemistry of kidney sections from human, rat, and mouse kidneys revealed that the MR is expressed in the cytosol of tubules staining positively for Lotus tetragonolobus agglutinin and type IIa sodium-phosphate cotransporter (NpT2a), confirming proximal tubule localization. Adrenalectomy in Sprague–Dawley rats decreased expression of MR, ENaC α, Na+, K+ ATPase α1, and NHE-1 in all tubules, while supplementation with aldosterone restored expression of above proteins. In human kidney proximal tubule (HKC11) cells, treatment with aldosterone resulted in translocation of MR to the nucleus and phosphorylation of SGK-1. Treatment with aldosterone also increased Na+, K+ ATPase-mediated 86Rb uptake and expression of Na+, K+ ATPase α1 subunits in HKC11 cells. The effects of aldosterone on Na+, K+ ATPase-mediated 86Rb uptake were prevented by spironolactone, a competitive inhibitor of aldosterone for the MR, and partially by Mifepristone, a glucocorticoid receptor (GR) inhibitor. These results suggest that aldosterone regulates Na+, K+ ATPase in renal proximal tubule cells through an MR-dependent mechanism.
•We demonstrate protein expression of MR in renal proximal tubules.•We demonstrate that aldosterone increases Na–K ATPase activity in renal proximal tubules.•We demonstrate that aldosterone acts through classical MR dependent pathway in PT.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The mechanisms underlying the development of aging-induced muscle atrophy are unclear. By microRNA array and individual qPCR analyses, we found significant up-regulation of miR-29 in muscles of aged ...rodents vs. results in young. With aging, p85α, IGF-1 and B-myb muscle levels were lower while the expression of certain cell arrest proteins (p53, p16 and pRB) increased. When miR-29 was expressed in muscle progenitor cells (MPC), their proliferation was impaired while SA-βgal expression increased signifying the development of senescence. Impaired MPC proliferation resulted from interactions between miR-29 and the 3'-UTR of p85a, IGF-1 and B-myb, suppressing the translation of these mediators of myoblast proliferation. In vivo, electroporation of miR-29 into muscles of young mice suppressed the proliferation and increased levels of cellular arrest proteins, recapitulating aging-induced responses in muscle. A potential stimulus of miR-29 expression is Wnt-3a since we found that exogenous Wnt-3a stimulated miR-29 expression 2.7-fold in primary cultures of MPCs. Thus, aging-induced muscle senescence results from activation of miR-29 by Wnt-3a leading to suppressed expression of several signaling proteins (p85α, IGF-1 and B-myb) that act coordinately to impair the proliferation of MPCs contributing to muscle atrophy. The increase in miR-29 provides a potential mechanism for aging-induced sarcopenia.
Vasopressin increases urine concentration through activation of aquaporin-2 (AQP2) in the collecting duct. Nonsteroidal anti-inflammatory drugs (NSAIDs) block prostaglandin E2 synthesis, and may ...suppress AQP2 producing a urine concentrating defect. There are four serines in AQP2 that are phosphorylated by vasopressin. To determine if chronic use of NSAIDs changes AQP2's phosphorylation at any of these residues, the effects of a non-selective NSAID, ibuprofen, and a COX-2-selective NSAID, meloxicam, were investigated. Daily ibuprofen or meloxicam increased the urine output and decreased the urine osmolality significantly by days 7 through 14. Concomitantly, meloxicam significantly reduced total AQP2 protein abundance in inner medulla (IM) tip to 64% of control and base to 63%, respectively. Ibuprofen significantly decreased total AQP2 in IM tip to 70% of control, with no change in base. Meloxicam significantly increased the ratios of p256-AQP2 and p261-AQP2 to total AQP2 in IM tip (to 44% and 40%, respectively). Ibuprofen increased the ratio of p256-AQP2 to total AQP2 in IM tip but did not affect p261-AQP2/total AQP2 in tip or base. Both ibuprofen and meloxicam increased p264-AQP2 and p269-AQP2 ratios in both tip and base. Ibuprofen increased UT-A1 levels in IM tip, but not in base. We conclude that NSAIDs reduce AQP2 abundance, contributing to decreased urine concentrating ability. They also increase some phosphorylated forms of AQP2. These changes may partially compensate for the decrease in AQP2 abundance, thereby lessening the decrease in urine osmolality.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Vasopressin triggers the phosphorylation and apical plasma membrane accumulation of aquaporin 2 (AQP2), and it plays an essential role in urine concentration. Vasopressin, acting through protein ...kinase A, phosphorylates AQP2. However, the phosphorylation state of AQP2 could also be affected by the action of protein phosphatases (PPs). Rat inner medullas (IM) were incubated with calyculin (PP1 and PP2A inhibitor, 50 nM) or tacrolimus (PP2B inhibitor, 100 nM). Calyculin did not affect total AQP2 protein abundance (by Western blot) but did significantly increase the abundances of pS256-AQP2 and pS264-AQP2. It did not change pS261-AQP2 or pS269-AQP2. Calyculin significantly enhanced the membrane accumulation (by biotinylation) of total AQP2, pS256-AQP2, and pS264-AQP2. Likewise, immunohistochemistry showed an increase in the apical plasma membrane association of pS256-AQP2 and pS264-AQP2 in calyculin-treated rat IM. Tacrolimus also did not change total AQP2 abundance but significantly increased the abundances of pS261-AQP2 and pS264-AQP2. In contrast to calyculin, tacrolimus did not change the amount of total AQP2 in the plasma membrane (by biotinylation and immunohistochemistry). Tacrolimus did increase the expression of pS264-AQP2 in the apical plasma membrane (by immunohistochemistry). In conclusion, PP1/PP2A regulates the phosphorylation and apical plasma membrane accumulation of AQP2 differently than PP2B. Serine-264 of AQP2 is a phosphorylation site that is regulated by both PP1/PP2A and PP2B. This dual regulatory pathway may suggest a previously unappreciated role for multiple phosphatases in the regulation of urine concentration.
In the late 1980s, urea permeability measurements produced values that could not be explained by paracellular transport or lipid phase diffusion. The existence of urea transport proteins were thus ...proposed and less than a decade later, the first urea transporter was cloned. The family of urea transporters has two major subgroups, designated
SLC14A1
(or UT-B) and
Slc14A2
(or UT-A). UT-B and UT-A gene products are glycoproteins located in various extra-renal tissues however, a majority of the resulting isoforms are found in the kidney. The UT-B (
Slc14A1
) urea transporter was originally isolated from erythrocytes and two isoforms have been reported. In kidney, UT-B is located primarily in the descending vasa recta. The UT-A (
Slc14A2
) urea transporter yields six distinct isoforms, of which three are found chiefly in the kidney medulla. UT-A1 and UT-A3 are found in the inner medullary collecting duct (IMCD), while UT-A2 is located in the thin descending limb. These transporters are crucial to the kidney’s ability to concentrate urine. The regulation of urea transporter activity in the IMCD involves acute modification through phosphorylation and subsequent movement to the plasma membrane. UT-A1 and UT-A3 accumulate in the plasma membrane in response to stimulation by vasopressin or hypertonicity. Long-term regulation of the urea transporters in the IMCD involves altering protein abundance in response to changes in hydration status, low protein diets, or adrenal steroids. Urea transporters have been studied using animal models of disease including diabetes mellitus, lithium intoxication, hypertension, and nephrotoxic drug responses. Exciting new genetically engineered mouse models are being developed to study these transporters.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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