Parathyroid hormone-related protein detection and interaction with NO and cyclic AMP in the renovascular system

The Molecular Mechanisms Underlying the Systemic Effects Mediated by Parathormone in the Context of Chronic Kidney Disease

Chronic kidney disease (CKD) stands as a prominent non-communicable ailment, significantly impacting life expectancy. Physiopathology stands mainly upon the triangle represented by parathormone-Vitamin D-Fibroblast Growth Factor-23. Parathormone (PTH), the key hormone in mineral homeostasis, is one of the less easily modifiable parameters in CKD; however, it stands as a significant marker for assessing the risk of complications. The updated "trade-off hypothesis" reveals that levels of PTH spike out of the normal range as early as stage G2 CKD, advancing it as a possible determinant of systemic damage. The present review aims to review the effects exhibited by PTH on several organs while linking the molecular mechanisms to the observed actions in the context of CKD. From a diagnostic perspective, PTH is the most reliable and accessible biochemical marker in CKD, but its trend bears a higher significance on a patient's prognosis rather than the absolute value. Classically, PTH acts in a dichotomous manner on bone tissue, maintaining a balance between formation and resorption. Under the uremic conditions of advanced CKD, the altered intestinal microbiota majorly tips the balance towards bone lysis. Probiotic treatment has proven reliable in animal models, but in humans, data are limited. Regarding bone status, persistently high levels of PTH determine a reduction in mineral density and a concurrent increase in fracture risk. Pharmacological manipulation of serum PTH requires appropriate patient selection and monitoring since dangerously low levels of PTH may completely inhibit bone turnover. Moreover, the altered mineral balance extends to the cardiovascular system, promoting vascular calcifications. Lastly, the involvement of PTH in the Renin-Angiotensin-Aldosterone axis highlights the importance of opting for the appropriate pharmacological agent should hypertension develop.

Disrupted tubular parathyroid hormone/parathyroid hormone receptor signaling and damaged tubular cell viability possibly trigger postsurgical kidney injury in patients with advanced hyperparathyroidism

BACKGROUND

Parathyroidectomy (PTX) that alleviates clinical manifestations of advanced hyperparathyroidism, including hypercalcemia and hypophosphatemia, is considered the best protection from calcium overload in the kidney. However, little is known about the relationship between postsurgical robust parathyroid hormone (PTH) reduction and perisurgical renal tubular cell viability. Post-PTX kidney function is still a crucial issue for primary hyperparathyroidism (PHPT) and tertiary hyperparathyroidism after kidney transplantation (THPT).

METHODS

As a clinical study, we examined data from 52 consecutive patients (45 with PHPT, 7 with THPT) who underwent PTX in our center between 2015 and 2017 to identify post-PTX kidney injury. Their clinical data, including urinary liver-type fatty acid-binding protein (L-FABP), a tubular biomarker for acute kidney injury (AKI), were obtained from patient charts. An absolute change in serum creatinine level of 0.3 mg/dL (26.5 µmol/L) on Day 2 after PTX defines AKI. Post-PTX calcium supplement dose adjustment was performed to strictly maintain serum calcium at the lower half of the normal range. To mimic post-PTX-related kidney status, a unique parathyroidectomized rat model was produced as follows: 13-week-old rats underwent thyroparathyroidectomy (TPTX) and/or 5/6 subtotal nephrectomy (NX). Indicated TPTX rats were given continuous infusion of a physiological level of 1-34 PTH using a subcutaneously implanted osmotic minipump. Immunofluorescence analyses were performed by polyclonal antibodies against PTH receptor (PTHR) and a possible key modulator of kidney injury, Klotho.

RESULTS

Patients' estimated glomerular filtration rate (eGFR) did not have any clinically relevant change (62.5 ± 22.0 versus 59.4 ± 21.9 mL/min/1.73 m2, NS), whereas serum calcium (2.7 ± 0.18 versus 2.2 ± 0.16 mmol/L, P < 0.0001) and phosphorus levels (0.87 ± 0.19 versus 1.1 ± 0.23 mmol/L, P < 0.0001) were normalized and PTH decreased robustly (181 ± 99.1 versus 23.7 ± 16.8 pg/mL, P < 0.0001) after successful PTX. However, six patients who met postsurgical AKI criteria had lower eGFR and greater L-FABP than those without AKI. Receiver operating characteristics (ROC) analysis revealed eGFR <35 mL/min/1.73 m2 had 83% accuracy. Strikingly, L-FABP >9.8 µg/g creatinine had 100% accuracy in predicting post-PTX-related AKI. Rat kidney PTHR expression was lower in TPTX. PTH infusion (+PTH) restored tubular PTHR expression in rats that underwent TPTX. Rats with TPTX, +PTH and 5/6 NX had decreased PTHR expression compared with those without 5/6 NX. 5/6 NX partially cancelled tubular PTHR upregulation driven by +PTH. Tubular Klotho was modestly expressed in normal rat kidneys, whereas enhanced patchy tubular expression was identified in 5/6 NX rat kidneys. This Klotho and expression and localization pattern was absolutely canceled in TPTX, suggesting that PTH indirectly modulated the Klotho expression pattern. TPTX +PTH recovered tubular Klotho expression and even triggered diffusely abundant Klotho expression. 5/6 NX decreased viable tubular cells and eventually downregulated tubular Klotho expression and localization.

CONCLUSIONS

Preexisting tubular damage is a potential risk factor for AKI after PTX although, overall patients with hyperparathyroidism are expected to keep favorable kidney function after PTX. Patients with elevated tubular cell biomarker levels may suffer post-PTX kidney impairment even though calcium supplement is meticulously adjusted after PTX. Our unique experimental rat model suggests that blunted tubular PTH/PTHR signaling may damage tubular cell viability and deteriorate kidney function through a Klotho-linked pathway.

Urinary excretion of parathyroid hormone-related protein correlates with renal function in control rats and rats with cisplatin nephrotoxicity

Parathyroid hormone-related protein (PTHrP) and its receptor are abundantly expressed throughout the renal parenchyma, where PTHrP exerts a modulatory action on renal function. PTHrP upregulation is a common event associated with the mechanism of renal injury and repair. However, no study has yet explored the putative excretion of PTHrP in urine, including its potential relationship with renal function. In the present study, we tested this hypothesis by studying the well-known rat model of acute renal injury induced by the chemotherapeutic agent cisplatin. Using Western blot analysis, we could detect a single protein band, corresponding to intact PTHrP, in the urine of both control and cisplatin-injected rats, whose levels were significantly higher in the latter group. PTHrP was detected in rat urine by dot blot, and its quantification with two specific ELISA kits showed that, compared with control rats, those treated with cisplatin displayed a significant increase in urinary PTHrP (expressed as the PTHrP-to-creatinine ratio or 24-h excretion). In addition, a positive correlation between urinary PTHrP excretion and serum creatinine was found in these animals. In conclusion, our data demonstrate that PTHrP is excreted in rat urine and that this excretion is higher with the decrease of renal function. This suggests that urinary PTHrP levels might be a renal function marker.

Mechanisms of PTHrP-induced inhibition of smooth muscle contractility in the guinea pig gastric antrum

BACKGROUND

Parathyroid hormone-related protein (PTHrP) that causes hypercalcemia of malignancy appears to function as an endogenous smooth muscle relaxant. For example, PTHrP released upon bladder wall distension relaxes detrusor smooth muscle to accommodate urine. Here, we explored mechanisms underlying PTHrP-induced suppression of the smooth muscle contractility in the gastric antrum that also undergoes a passive distension.

METHODS

Effects of PTHrP on phasic contractions and electrical slow waves in the antral smooth muscle of the guinea pig stomach were studied using isometric tension and intracellular microelectrode recordings, respectively. Fluorescent immunohistochemistry was also carried out to identify the distribution of PTH/PTHrP receptors.

KEY RESULTS

Parathyroid hormone-related protein (1-100 nM) reduced the amplitude of phasic contractions and the basal tension. N^ω -nitro-l-arginine (L-NA, 100 μM), a nitric oxide (NO) synthase inhibitor, or 1H-[1,2,4]oxadiazolo-[4, 3-a]quinoxalin-1-one (ODQ, 10 µM), a guanylate cyclase inhibitor, diminished the PTHrP (10 nM)-induced reduction in the amplitude of phasic contractions. SQ22536 (300 μM), an adenylate cyclase inhibitor, attenuated the PTHrP-induced reduction in basal tension. The combination of ODQ (10 μM) and SQ22536 (300 μM) inhibited the PTHrP-induced reductions in both phasic contractions and basal tension. PTHrP (100 nM) had no inhibitory effect on the electrical slow waves in the antral smooth muscle. PTH/PTHrP receptors were expressed in cell bodies of PGP9.5-positive neurons in the myenteric plexus.

CONCLUSIONS & INFERENCES

Parathyroid hormone-related protein exerts its inhibitory actions on the antral smooth muscle via both nitric oxide-cyclic guanosine monophosphate (NO-cGMP) and cyclic adenosine monophosphate (AMP) pathways. Thus, PTHrP may act as an endogenous relaxant of the gastric antrum employing the two complementary signaling pathways to ensure the adaptive relaxation of stomach.

Knockdown of parathyroid hormone related protein in smooth muscle cells alters renal hemodynamics but not blood pressure

Parathyroid hormone-related protein (PTHrP) belongs to vasoactive factors that regulate blood pressure and renal hemodynamics both by reducing vascular tone and raising renin release. PTHrP is expressed in systemic and renal vasculature. Here, we wanted to assess the contribution of vascular smooth muscle cell endogenous PTHrP to the regulation of cardiovascular and renal functions. We generated a mouse strain (SMA-CreERT2/PTHrPL2/L2 or premutant PTHrPSM-/-), which allows temporally controlled, smooth muscle-targeted PTHrP knockdown in adult mice. Tamoxifen treatment induced efficient recombination of PTHrP-floxed alleles and decreased PTHrP expression in vascular and visceral smooth muscle cells of PTHrPSM-/- mice. Blood pressure remained unchanged in PTHrPSM-/- mice, but plasma renin concentration and creatinine clearance were reduced. Renal hemodynamics were further analyzed during clearance measurements in anesthetized mice. Conditional knockdown of PTHrP decreased renal plasma flow and glomerular filtration rate with concomitant reduction in filtration fraction. Similar measurements were repeated during acute saline volume expansion. Saline volume expansion induced a rise in renal plasma flow and reduced filtration fraction; both were blunted in PTHrPSM-/- mice leading to impaired diuresis. These findings show that endogenous vascular smooth muscle PTHrP controls renal hemodynamics under basal conditions, and it is an essential factor in renal vasodilation elicited by saline volume expansion.

Parathyroid hormone-related protein stimulates plasma renin activity via its anorexic effects on sodium chloride intake

Parathyroid hormone-related protein (PTHrP) increases renin release from isolated perfused kidneys and may act as an autacoid regulator of renin secretion, but its effects on renin in vivo are unknown. In vivo, PTHrP causes hypercalcemia and anorexia, which may affect renin. We hypothesized that chronically elevated PTHrP would increase plasma renin activity (PRA) indirectly via its anorexic effects, reducing sodium chloride (NaCl) intake and causing NaCl restriction. We infused male Sprague-Dawley rats with the vehicle (control) or 125 μg PTHrP/day (PTHrP) via subcutaneous osmotic minipumps for 5 days. To replenish NaCl consumption, a third group of PTHrP-infused rats received 0.3% NaCl (PTHrP + NaCl) in their drinking water. PTHrP increased PRA from a median control value of 3.68 to 18.4 ng Ang I·ml(-1)·h(-1) (P < 0.05), whereas the median PTHrP + NaCl PRA value was normal (7.82 ng Ang I·ml(-1)·h(-1), P < 0.05 vs. PTHrP). Plasma Ca(2+) (median control: 10.2 mg/dl; PTHrP: 13.7 mg/dl; PTHrP + NaCl: 14.1 mg/dl; P < 0.05) and PTHrP (median control: 0.03 ng/ml; PTHrP: 0.12 ng/ml; PTHrP + NaCl: 0.15 ng/ml; P < 0.05) were elevated in PTHrP- and PTHrP + NaCl-treated rats. Body weights and caloric consumption were lower in PTHrP- and PTHrP + NaCl-treated rats. NaCl consumption was lower in PTHrP-treated rats (mean Na(+): 28.5 ± 4.1 mg/day; mean Cl(-): 47.8 mg/day) compared with controls (Na(+): 67.3 ± 2.7 mg/day; Cl(-): 112.8 ± 4.6 mg/day; P < 0.05). NaCl consumption was comparable with control in the PTHrP + NaCl group; 0.3% NaCl in the drinking water had no effect on PRA in normal rats. Thus, our data support the hypothesis that PTHrP increases PRA via its anorexic effects, reducing NaCl intake and causing NaCl restriction.

A transgenic mouse model for studying the role of the parathyroid hormone-related protein system in renal injury

Parathyroid hormone- (PTH-) related protein (PTHrP) and its receptor, the PTH1 receptor (PTH1R), are widely expressed in the kidney, where PTHrP exerts a modulatory action on renal function. PTHrP is known to be upregulated in several experimental nephropathies such as acute renal failure (ARF), obstructive nephropathy (ON) as well as diabetic nephropathy (DN). In this paper, we will discuss the functional consequences of chronic PTHrP overexpression in the damaged kidney using a transgenic mouse strain overexpressing PTHrP in the renal proximal tubule. In both ARF and ON, PTHrP displays proinflammatory and profibrogenic actions including the induction of epithelia to mesenquima transition. Moreover, PTHrP participates in the mechanisms of renal hypertrophy as well as proteinuria in experimental DN. Angiotensin II (Ang II), a critical factor in the progression of renal injury, appears to be, at least in part, responsible for endogenous PTHrP upregulation in these pathophysiological settings. These findings provide novel insights into the well-known protective effects of Ang II antagonists in renal diseases, paving the way for new therapeutic approaches.

Vasodilatory effect of tuberoinfundibular peptide (TIP39): requirement of receptor desensitization and its beneficial effect in the post-ischemic heart

Tuberoinfundibular peptide of 39 residues (TIP39) is a member of the parathyroid hormone (PTH) family and a highly specific ligand of the PTH-receptor type 2 (PTH-2r). Recent studies have shown vasoactive properties of TIP39 in the kidney. This effect was stronger after desensitization of the parathyroid hormone-receptor type 1 (PTH-1r). The aims of our study were three-fold: (1) to investigate the influence of TIP39 on coronary resistance (CR), (2) to investigate a possible cross-talk between vascular PTH-receptors in the cardiovascular system, and (3) to investigate whether the endogenously released PTHrP during ischemia induces such a desensitizing effect. Experiments were performed on isolated rat hearts that were perfused with a constant pressure (Langendorff mode) and the coronary flow was determined. Under basal conditions, TIP39 showed no influences on CR. However, TIP39 reduced the CR by approximately 22% after pre-treatment of the hearts with a PTH-1r agonist. This TIP39 effect was abolished either by co-administration of a PTH-2r antagonist or by inhibition of nitric oxide (NO) formation. In an ischemia-reperfusion model endogenously released PTHrP desensitized the PTH-1r and pre-ischemic addition of TIP39 reduced post-ischemic CR by about 28%. Again, this effect was completely abolished in the presence of the PTH-2r antagonist or the PTH-1r-antagonist or by inhibition of NO formation. However, no effect was observed when TIP39 was washed-out prior to ischemia or if the treatment with TIP39 was restricted to the reperfusion. Furthermore, a pre-ischemic application of the NO-dependent vasorelaxant bradykinin provoked a similar effect on the post-ischemic CR than TIP39. In conclusion, a NO-dependent vasodilatory effect of TIP39 was demonstrated if the PTH-1r is desensitized by either exogenously applicated PTHrP peptides or endogenously released PTHrP.

The parathyroid hormone-related protein system and diabetic nephropathy outcome in streptozotocin-induced diabetes

The pathophysiology of the diabetic kidney (e.g., hypertrophy, increase urinary albumin excretion (UAE) is still ill-defined. Parathyroid hormone-related protein (PTHrP) is overexpressed in several nephropathies, but its role remains unclear. We evaluated the effect of high glucose on PTHrP and the PTH1 receptor (PTH1R) protein (by Western blot and immunohistochemistry) in the kidney of mice ith streptozotocin-induced diabetes, and in several mouse renal cells in vitro. Diabetic mice showed a significantly increased renal expression of PTHrP and PTH1R proteins with 2-8 weeks from the onset of diabetes. These animals exhibited an intense immunostaining for both proteins in the renal tubules and glomeruli. Using transgenic mice overexpressing PTHrP targeted to the renal proximal tubule, we found a significant increase in the renal hypertrophy index and in UAE in these diabetic mice relative to their control littermates. Moreover, logistic regression analysis showed a significant association between both PTHrP and PTH1R protein levels and UAE in all diabetic mice throughout the study. High-glucose (25 mm) medium was found to increase PTHrP and PTH1R in tubuloepithelial cells, mesangial cells and podocytes in vitro. Moreover, this increase in PTHrP (but not that of PTH1R) was inhibited by the AT1 receptor antagonist losartan. Collectively, these results indicate that the renal PTHrP/PTH1R system is upregulated in streptozotozin-induced diabetes in mice, and appears to adversely affect the outcome of diabetic renal disease. Our findings also suggest that angiotensin II might have a role in the PTHrP upregulation in this condition.

Antitumor effect of parathyroid hormone-related protein neutralizing antibody in human renal cell carcinoma in vitro and in vivo

Functional inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene occurs in 40-80% of human conventional renal cell carcinomas (RCCs). We showed recently that VHL-deficient RCCs expressed large amounts of parathyroid hormone-related protein (PTHrP), and that PTHrP, acting through the PTH1 receptor (PTH1R), plays an essential role in tumor growth. We also showed that PTHrP expression is negatively regulated by the VHL gene products (pVHL). Our goal was to determine whether blocking the PTHrP/PTH1R system might be of therapeutic value against RCC, independent of VHL status and PTHrP expression levels. The antitumor activity of PTHrP neutralizing antibody and of PTH1R antagonist were evaluated in vitro and in vivo in a panel of human RCC lines expressing or not pVHL. PTHrP is upregulated compared with normal tubular cells. In vitro, tumor cell growth and viability was decreased by up to 80% by the antibody in all cell lines. These effects resulted from apoptosis. Exogenously added PTHrP had no effect on cell growth and viability, but reversed the inhibitory effects of the antibody. The growth inhibition was reproduced by a specific PTH1R antagonist in all cell lines. In vivo, the treatment of nude mice bearing the Caki-1 RCC tumor with the PTHrP antibody inhibited tumor growth by 80%, by inducing apoptosis. Proliferation and neovascularization were not affected by the antiserum. Anti-PTHrP treatment induced no side effects as assessed by animal weight and blood chemistries. Current therapeutic strategies are only marginally effective against metastatic RCC, and adverse effects are common. This study provides a rationale for evaluating the blockade of PTHrP signaling as therapy for human RCC in a clinical setting.

Parathyroid hormone-related protein-mediated responses in pulmonary arteries and veins of newborn lambs

PTHrP has important roles in lung development and function. Here we determined the vasomotor responses of isolated pulmonary arteries and veins of newborn and adult sheep to PTHrP. In vessels constricted with endothelin-1, PTHrP (PTHrP 1-34) caused greater relaxation of veins than of arteries. In both vessel types, relaxation to the peptide was less in adult than in newborn vessels. In newborn lambs, PTHrP-induced relaxation was not affected by endothelium removal, inhibition of eNOS, or inhibition of adenylyl cyclases by SQ-22536. However, relaxation was attenuated by 4-aminopyridine, inhibitor of voltage-dependent potassium channels, in both arteries and veins, and by charybdotoxin, inhibitor of calcium-activated potassium channels, in veins. When vessels were saturated with 8-BrcAMP (3 x 10(-4) M), to eliminate relaxation mediated by endogenous cAMP, PTHrP-induced relaxation was partially attenuated. In vessels treated with 8-BrcAMP (3 x 10(-4) M), 4-aminopyridine but not charybdotoxin inhibited relaxation induced by PTHrP 1-34 in both arteries and veins. Radioimmunoassay showed that, in the presence of a general phosphodiesterase inhibitor, PTHrP caused a concentration-dependent increase in intracellular cAMP content in arteries and veins, which was largely abolished by SQ-22536. Our results demonstrate that PTHrP is a potent vasodilator of pulmonary vessels, with a greater effect in veins than in arteries. Relaxation induced by the peptide contains both cAMP-dependent and -independent components. In both arteries and veins, voltage-dependent potassium channels mediate the response to PTHrP, at least in part, in a cAMP-independent fashion; and in veins, calcium-activated potassium channels may be stimulated by elevated cAMP levels.

Role of the Renin-Angiotensin System on the Parathyroid Hormone–Related Protein Overexpression Induced by Nephrotoxic Acute Renal Failure in the Rat

Parathyroid hormone-related protein (PTHrP), a mitogenic factor for renal cells, is overexpressed in acute renal failure (ARF). Recent data support an association between PTHrP and the renin-angiotensin system in the damaged kidney. The effects of angiotensin II (Ang II) inhibitors (quinapril, enalapril, and/or losartan) on PTHrP and the PTH1 receptor (PTH1R) expression in rats with either folic acid (FA)- or gentamicin-induced ARF were analyzed. The decreased renal function and the PTHrP upregulation and PTH1R downregulation induced by the nephrotoxins were inhibited by the Ang II blockers. In tubuloepithelial cells NRK-52E, the rapid (10 min) increase in PTHrP mRNA by FA, associated with a perinuclear relocalization of Ang II/AT1 receptor, was inhibited by losartan but not candesartan, which traps Ang II receptors at the cell surface. Maximal PTHrP protein overexpression by FA (at 24 to 72 h)-or by exogenous Ang II-was abolished by both Ang II antagonists. PTHrP upregulation by FA was preceded by increased extracellular signal-regulated kinase (ERK) phosphorylation and inhibited by the ERK inhibitor PD098059. FA also activated cAMP response element-binding (CREB) protein, and this was prevented by losartan in these cells. Moreover, PTHrP mRNA overexpression by either FA or Ang II occurred in NRK 52E that were transfected with a CREB construct but not the dominant-negative CREB133 construct. These findings demonstrate that the decreased renal function and PTHrP overexpression in nephrotoxin-damaged kidney depends on renin-angiotensin system. In this setting, intracellular Ang II/AT1 receptor recycling seems to be related to PTHrP induction through ERK and CREB activation in tubuloepithelial cells.

Altered renal hemodynamics in mice overexpressing the parathyroid hormone (PTH)/PTH-related peptide type 1 receptor in smooth muscle

PTH-related protein (PTHrP) is an autocrine/paracrine peptide expressed in renal tubules and vasculature and may play an important role in regulating overall renal function. To evaluate the potential role of endogenous PTHrP in the control of renal hemodynamics, we performed clearance measurements in transgenic (TG) mice in which the SMP8 alpha-actin promoter was used to drive overexpression of the PTH/PTHrP type 1 receptor in smooth muscle. In protocol I, responses to acute saline volume expansion (SVE, 0.75 microl/min.g body weight) were measured in TG and nontransgenic (NTG) mice. Mean arterial pressure was significantly lower in TG mice throughout the experiment, and it decreased comparably in both groups in response to SVE. SVE significantly increased effective renal plasma flow in both groups of mice, but the increase was greater in TG than in NTG. Glomerular filtration rate decreased in response to SVE in NTG but did not change in TG animals. In protocol II, renal responses to angiotensin II (ANG II) infusion were determined (0.5 ng/min.g body weight). Baseline arterial pressure was again significantly lower in TG, compared with NTG mice, and TG mice had a blunted pressor response to ANG II. Also, ANG II decreased effective renal plasma flow and glomerular filtration rate in both groups of animals, but the reductions were less in TG than in NTG mice. Our findings indicate that smooth-muscle-specific overexpression of the PTH/PTHrP type 1 receptor resulted in augmentation of the vasodilatory response to SVE and attenuation of the vasoconstrictor response to ANG II. We conclude that endogenous PTHrP can act as an endogenous vasorelaxant factor to modulate renal responses to vasoactive stimuli.

Relaxant effects of parathyroid hormone and parathyroid hormone-related peptides on oviduct motility in birds and mammals: possible role of nitric oxide

Parathyroid hormone (PTH) and PTH-related peptides (PTHrP) have previously been shown to modulate the contractile state of numerous types of smooth muscle. The effects of N-terminal PTH and PTHrP on spontaneous in vitro contractility of oviducal smooth muscle using tissues from egg-laying Japanese quail (10-15 h post ovulation), 4 and 9 days pregnant mouse uterus were investigated. Myometrial tissues from both species contracted vigorously for several hours, when incubated in organ baths in De Jalon's solution gassed with 5%CO2/95%O2. Contractions were enhanced in high (1.2-2.5 mM) compared with low (0.1-0.5 mM) calcium (Ca) containing media. Bovine PTH(1-34) (bPTH(1-34)), human PTH(1-34 amide) (hPTHrP(1-34) amide), and hPTHrP(1-40) caused similar concentration-related inhibition of contractions in media containing 1.2mM Ca over a range of 10(-9) to 10(-7)M, whereas C-terminal hPTHrP(107-139) was devoid of such activity. Responses to bPTH(1-34) in 4 and 9-day pregnant mouse tissues were similar but hPTHrP(1-40) showed substantial loss of activity in 9-day, compared with 4-day pregnant mouse tissues. Repeated exposure of mouse uterine tissue to the peptides resulted in desensitisation of responses. The EC50 responses of mouse tissues were inhibited by the PTH/PTHrP receptor antagonist, hPTHrP(7-34) amide. Responses to bPTH(1-34) were also inhibited by both non-selective and selective neuronal nitric oxide synthase (NOS) inhibitors N(omega)-nitro-L-arginine methyl ester (0.01-1mM) and 7-nitroindazole (0.01-10 microM), respectively. Both NOS inhibitors were more effective in inhibiting bPTH(1-34)-induced relaxation in the absence of L-arginine compared with in the presence of 1mM L-arginine (a NOS substrate) in the incubation media. It is concluded that relaxant responses to N-terminal PTH and PTHrP peptides are well conserved in oviducal and uterine tissues from avian and mammalian species. The results also suggest that NO may be responsible for mediating relaxant activities of these peptides in pregnant mouse uterine tissue.

Parathyroid hormone-related protein induction in focal stroke: a neuroprotective vascular peptide

Parathyroid hormone-related protein (PTHrP) is a multifunctional peptide that enhances blood flow in non-central nervous system (CNS) vascular beds by causing vasodilation. PTHrP expression is induced in non-CNS organs in response to ischemia. Experiments were therefore undertaken to determine whether PTHrP can be induced in brain in response to ischemic injury and whether PTHrP can act locally as a vasodilator in the cerebral vasculature, an effect that could be neuroprotective in the setting of stroke. PTHrP expression was examined by Northern analysis and immunohistochemical staining in male Sprague-Dawley rats subjected to permanent middle cerebral artery occlusion (MCAO). Vasodilatory effects of superfused PTHrP(1-34) on pial arterioles were determined by intravital fluorescence microscopy. Effects of PTHrP(1-34) peptide administration on MCAO infarction size reduction were assessed. PTHrP expression was induced in the ischemic hemisphere as early as 4 h after MCAO and remained elevated for up to 24 h. Increased immunoreactive PTHrP at sites of ischemic tissue injury was located in the cerebral microvessels. Superfusion with PTHrP(1-34) peptide for up to 25 min increased pial arteriolar diameter by 30% in normal animals. In animals with permanent MCAO, PTHrP(1-34) peptide treatment significantly decreased cortical infarct size (-47%). In summary, PTHrP expression increases at sites of ischemic brain injury in the cerebrovasculature. This local increase in PTHrP could be an adaptive response that enhances blood flow to the ischemic brain, thus limiting cell injury.

Beneficial effects of calcimimetics on progression of renal failure and cardiovascular risk factors

In renal failure, parathyroid hormone (PTH) is not only involved in the genesis of disturbed calcium/phosphate metabolism and ostitis fibrosa; it is also a permissive factor in the genesis of hypertension, cardiovascular damage, and dyslipidemia. The allosteric activator of the calcium sensing receptor NPSR-568 (R-568) has been shown to reduce the serum intact PTH (iPTH) concentration in uremic rats. It was the purpose of this study in subtotally nephrectomized (SNX) rats to compare pharmacologic abrogation of secondary hyperparathyroidism by R-568 with parathyroidectomy (PTX). The effects on progression of renal failure, BP, and lipid and structural parameters of kidney and heart were studied. Four groups of male SD-rats were studied: (1) sham-operated + vehicle-treated rats (controls); (2) SNX + vehicle-treated rats (SNX); (3) parathyroidectomized SNX + vehicle-treated rats (SNX+PTX); and (4) SNX + calcimimetic R-568-treated rats (SNX+R-568). R-568 (50 micro mol/kg per d) was administered by gavage. Eight weeks after SNX, serum creatinine concentration, urinary albumin excretion, BP, and serum LDL-cholesterol concentration were significantly lower in both R-568-treated and parathyroidectomized SNX compared with vehicle-treated SNX. In addition, structural abnormalities of the kidney (glomerulosclerosis, tubulointerstitial changes) and the heart (interstitial fibrosis, capillary length density, arteriolar wall thickness) were significantly less pronounced than in vehicle-treated SNX. It is concluded that in experimental renal failure abrogation of hyperparathyroidism by administration of a calcimimetic or PTX similarly attenuates progression of renal failure. Furthermore, it interferes with the development of cardiovascular risk factors and cardiac remodeling.

Parathyroid hormone-related peptide improves contractile function of stunned myocardium in rats and pigs

The effect of synthetic parathyroid hormone (PTH)-related peptide [PTHrP(1-34)] on regional myocardial function was studied in 11 anesthetized pigs. Intracoronary infusion of PTHrP (cumulative dose: 14 +/- 1 microg) decreased coronary resistance to 33 +/- 2% of baseline (P < 0.05) and regional myocardial function to 90 +/- 3% of baseline (not significant). Ischemia-reperfusion alters the activity of several kinases and therefore possibly the myocardial effects of PTHrP. In stunned myocardium, induced by 20-min ischemia and 30-min reperfusion, the dose of PTHrP reducing coronary resistance to a minimum of 29 +/- 2% was decreased to 8 +/- 2 microg (P < 0.05). Regional myocardial function was no longer decreased but increased to 132 +/- 9% (P < 0.05). The increase in regional myocardial function during PTHrP was inversely related to baseline function at 30-min reperfusion in vivo (r = 0.9) as well as in myocytes isolated from stunned pig hearts (r = 0.7). In isolated rat hearts subjected to 30-min global ischemia followed by 30-min reperfusion, blockade of endogenous PTHrP by d-Trp(12)-Tyr(34)-PTH(7-34) attenuated the recovery of left ventricular developed pressure by 30 +/- 14% (P < 0.05). Thus endogenous and exogenous PTHrP impact on the function of stunned myocardium.

Angiotensin II increases parathyroid hormone-related protein (PTHrP) and the type 1 PTH/PTHrP receptor in the kidney

Angiotensin II (AngII) participates in the pathogenesis of kidney damage. Parathyroid hormone (PTH)-related protein (PTHrP), a vasodilator and mitogenic agent, is upregulated during renal injury. The aim of this study was to investigate the potential relation between AngII and PTHrP system in the kidney. Different methods were used to find that both rat mesangial and mouse tubuloepithelial cells express PTHrP and the type 1 PTH/PTHrP receptor (PTH1R). In these cells, AngII increased PTHrP mRNA and protein production. In contrast, PTH1R mRNA was increased in mesangial cells and downregulated in tubular cells, but its protein levels were unmodified in both cells. AT(1) antagonist, but not AT(2), abolished AngII effects on PTHrP/PTH1R. The in vivo effect of AngII was further investigated by systemic infusion (a low dose of 50 ng/kg per min) into normal rats. In controls, PTHrP immunostaining was mainly detected in renal tubules. In AngII-infused rats, PTHrP staining increased in renal tubules and appeared in the glomerulus and the renal vessels. After AngII infusion, PTHR1 staining was markedly increased in all these renal structures at day 3 but remained elevated only in tubules at day 7. The AT(1) antagonist, but not the AT(2), significantly diminished AngII-induced PTHrP and PTHR1 overexpression in the renal tissue, associated with a decrease in tubular damage and fibrosis. The results indicate that AngII regulates renal PTHrP/PTH1R system via AT(1) receptors. These findings demonstrate that PTHrP upregulation occurs in association with the mechanisms of AngII-induced kidney injury.

cAMP pathway in podocytes

Podocytes possess receptors for a variety of hormones. The following receptors whose stimulation results in increased cAMP levels have been detected in podocytes: adrenergic beta(2) receptor, dopamine D(1) receptor, prostaglandin IP and EP(4) receptors, and parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor. Besides activating protein kinase A, increased levels of cAMP depolarize podocytes via opening of chloride channels. Relatively little is known about the impact of the cAMP pathway on podocyte function. Results obtained in a limited number of studies indicate that cAMP in podocytes may regulate cell morphology, actin assembly, and matrix production. In addition, cAMP seems to attenuate the action of hormones, which activate the Ca(2+)/protein kinase C pathway. Effects of the cAMP pathway on further aspects of podocyte biology, such as contractility, phosphorylation state of slit membrane-associated proteins, glomerular permeability, cell cycle control, and synthesis of reactive oxygen species can be anticipated from studies on other cell types and from studies on isolated glomeruli. In summary, the data available indicate that the cAMP pathway affects several aspects of podocyte biology in an overall glomerulo-protective manner.

Type 1 parathyroid hormone receptor expression level modulates renal tone and plasma renin activity in spontaneously hypertensive rat

These studies examine whether PTHrP(1-36), a vasodilator, modulates BP and renal vascular resistance (RVR) in spontaneously hypertensive rat (SHR). Within the kidney of normotensive rats, PTHrP(1-36) was enriched in vessels. In vessels of SHR, PTHrP was upregulated by 40% and type 1 PTH receptor (PTH1R) was downregulated by 65% compared with normotensive rats. To investigate the role of endogenous PTHrP in the regulation of BP and RVR, SHR were subjected to somatic human (h)PTH1R gene delivery. Three weeks after a single intravenous injection of pcDNA1.1 plasmid containing the hPTH1R gene under the control of the cytomegalovirus promoter, hPTH1R mRNA was detected in all of the main organs. Within the kidney, the transgene was enriched in vessels. In the isolated perfused kidney, RVR was reduced by 23% and PTHrP(1-36)-induced vasodilation, which is depressed in SHR, was restored and a vasoconstrictory response to PTH(3-34), a PTH1R antagonist, was revealed. These effects were not observed in control SHR treated with empty plasmid. BP remained unchanged, and plasma renin activity increased by 60%. Thus, in SHR renal vessels, a reduced number of PTH1R contributes to the high RVR, despite the higher expression of vasodilatory PTHrP. Moreover, these studies provide evidence for a direct link between the density of PTH1R and plasma renin activity, which might be responsible for the absence of effect of PTH1R gene delivery on BP in SHR. Overall, PTHrP significantly contributes to the homeostasis of renal and systemic hemodynamics in SHR.

Parathyroid hormone-related protein and its receptors: nuclear functions and roles in the renal and cardiovascular systems, the placental trophoblasts and the pancreatic islets

The cloning of the so-called 'parathyroid hormone-related protein' (PTHrP) in 1987 was the result of a long quest for the factor which, by mimicking the actions of PTH in bone and kidney, is responsible for the hypercalcemic paraneoplastic syndrome, humoral calcemia of malignancy. PTHrP is distinct from PTH in a number of ways. First, PTHrP is the product of a separate gene. Second, with the exception of a short N-terminal region, the structure of PTHrP is not closely related to that of PTH. Third, in contrast to PTH, PTHrP is a paracrine factor expressed throughout the body. Finally, most of the functions of PTHrP have nothing in common with those of PTH. PTHrP is a poly-hormone which comprises a family of distinct peptide hormones arising from post-translational endoproteolytic cleavage of the initial PTHrP translation products. Mature N-terminal, mid-region and C-terminal secretory forms of PTHrP are thus generated, each of them having their own physiologic functions and probably their own receptors. The type 1 PTHrP receptor, binding both PTH(1-34) and PTHrP(1-36), is the only cloned receptor so far. PTHrP is a PTH-like calciotropic hormone, a myorelaxant, a growth factor and a developmental regulatory molecule. The present review reports recent aspects of PTHrP pharmacology and physiology, including: (a) the identification of new peptides and receptors of the PTH/PTHrP system; (b) the recently discovered nuclear functions of PTHrP and the role of PTHrP as an intracrine regulator of cell growth and cell death; (c) the physiological and developmental actions of PTHrP in the cardiovascular and the renal glomerulo-vascular systems; (d) the role of PTHrP as a regulator of pancreatic beta cell growth and functions, and, (e) the interactions of PTHrP and calcium-sensing receptors for the control of the growth of placental trophoblasts. These new advances have contributed to a better understanding of the pathophysiological role of PTHrP, and will help to identify its therapeutic potential in a number of diseases.

Up-regulation of parathyroid hormone-related protein in folic acid-induced acute renal failure

BACKGROUND

Parathyroid hormone (PTH)-related protein (PTHrP) is present in many normal tissues, including the kidney. Current evidence supports that PTHrP is involved in renal pathophysiology, although its role on the mechanisms of renal damage and/or repair is unclear. Our present study examined the changes in PTHrP and the PTH/PTHrP receptor (type 1) in folic acid-induced acute renal failure in rats. The possible role of PTHrP on the process of renal regeneration following folic acid administration, and potential interaction between angiotensin II (Ang II) and endothelin-1, and PTHrP, were examined in this animal model.

METHODS

PTHrP, PTH/PTHrP receptor, ACE, and preproendothelin-1 (preproET-1) mRNA levels in the rat kidney were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and/or RNase protection assay. Immunohistochemistry also was performed for PTHrP, the PTH/PTHrP receptor, and Ang II in the renal tissue of folic acid-injected rats. The role of PTHrP on tubular cell proliferation following folic acid injury was investigated in vitro in rat renal epithelial cells (NRK 52E). PTHrP secretion in the medium conditioned by these cells was measured by an immunoradiometric assay specific for the 1-36 sequence.

RESULTS

Using RT-PCR, PTHrP mRNA was rapidly (1 hour) and maximally increased (3-fold) in the rat kidney after folic acid, decreasing after six hours. At 72 hours, renal function was maximally decreased in these rats, associated with an increased PTHrP immunostaining in both renal tubules and glomeruli. In contrast, the PTH/PTHrP receptor mRNA (RNase protection assay) decreased shortly after folic acid administration. Moreover, PTH/PTHrP receptor immunostaining dramatically decreased in renal tubular cell membranes after folic acid. A single subcutaneous administration of PTHrP (1-36), 3 or 50 microg/kg body weight, shortly after folic acid injection increased the number of tubular cells staining for proliferating cell nuclear antigen by 30% (P < 0.05) or 50% (P < 0.01), respectively, in these rats at 24 hours, without significant changes in either renal function or calcemia. On the other hand, this peptide failed to modify the increase (2-fold over control) in ACE mRNA, associated with a prominent Ang II staining into tubular cell nuclei, in the kidney of folic acid-treated rats at this time period. The addition of 10 mmol/L folic acid to NRK 52E cells caused a twofold increase in PTHrP mRNA at six hours, without significant changes in the PTH/PTHrP receptor mRNA. The presence of two anti-PTHrP antibodies, with or without folic acid, in the cell-conditioned medium decreased (40%, P < 0.01) cell growth.

CONCLUSIONS

Renal PTHrP was rapidly and transiently increased in rats with folic acid-induced acute renal failure, featuring as an early response gene. In addition, changes in ACE and Ang II expression were also found in these animals. PTHrP induces a mitogenic response in folic acid-damaged renal tubular cells both in vivo and in vitro. Our results support the notion that PTHrP up-regulation participates in the regenerative process in this model of acute renal failure and is a common event associated with the mechanisms of renal injury and repair.

The C-terminal region of PTHrP, in addition to the nuclear localization signal, is essential for the intracrine stimulation of proliferation in vascular smooth muscle cells

PTHrP is secreted by most cell types. In addition to a paracrine/autocrine role, PTHrP has "intracrine" actions, entering the nuclear compartment under the direction of a classic bipartite nuclear localization signal. In vascular smooth muscle cells, nuclear entry stimulates mitogenesis. In the current study, we sought to more precisely define the regions of PTHrP required for the activation of mitogenesis in vascular smooth muscle cells. PTHrP deletion mutants missing large regions [i.e. the signal peptide, N terminus (1--36), mid region (38--86), nuclear localization signal, C terminus (108--139), or combinations of the above] were expressed in A-10 vascular smooth muscle cells. The consequences on nuclear localization and proliferation were examined. Deletion of the nuclear localization signal prevented nuclear entry and slowed proliferation. Deletion of the highly conserved N terminus or mid region had no impact on nuclear localization or on proliferation. Deletion of the C terminus had no deleterious effect on nuclear localization but dramatically reduced proliferation. Thus, the nuclear localization signal is both necessary and sufficient for nuclear localization of PTHrP. In contrast, activation of proliferation in vascular smooth muscle cells requires both an intact nuclear localization signal and an intact C terminus. Whereas the nuclear localization signal is required for nuclear entry, the C terminus may serve a trans-activating function to stimulate mitogenesis once inside the nucleus of vascular smooth muscle cells.

Parathyroid hormone-related protein-(1-34) inhibits intrinsic pump activity of isolated murine lymph vessels

Parathyroid hormone-related protein (PTHrP) was originally found as a tumor-derived vasoactive factor and has also been known to produce significant relaxation of vascular smooth muscles. Thus effects of PTHrP-(1-34), a PTH receptor-binding domain, on spontaneous lymphatic pump activity was investigated in isolated pressurized lymph vessels of mice. Low concentrations (1 x 10(-10) and 3 x 10(-10) M) of PTHrP-(1-34) dilated lymph vessels and reduced the frequency of pump activity, whereas high concentrations (1 x 10(-9) to 1 x 10(-8) M) of PTHrP-(1-34) caused dilation with cessation of the lymphatic pump activity. N(omega)-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-5) M) but not indomethacin (1 x 10(-5) M) significantly reduced the PTHrP-(1-34)-induced inhibitory responses of the lymphatic pump activity. In the presence of L-NAME (3 x 10(-5) M) and L-arginine (1 x 10(-3) M), the L-NAME-induced inhibition in the PTHrP-(1-34)-mediated responses was significantly reduced. Glibenclamide (1 x 10(-6) M) significantly suppressed the inhibitory responses of the lymphatic pump activity induced by PTHrP-(1-34) and S-nitroso-N-acetyl-penicillamine. The PTHrP-(1-34)-mediated inhibitory responses were significantly reduced by treatment with PTHrP-(7-34) (1 x 10(-7) M). These results suggest that PTHrP-(1-34) inhibits spontaneous pump activity of the isolated lymph vessels via PTH receptors and that production and release of endogenous nitric oxide and activation of ATP-sensitive K(+) channels in the lymph vessels contribute to the PTHrP-(1-34)-mediated inhibitory responses of the lymphatic pump activity.

Paradoxical actions of exogenous and endogenous parathyroid hormone-related protein on renal vascular smooth muscle cell proliferation: reversion in the SHR model of genetic hypertension

In previous studies, added parathyroid hormone-related protein (PTHrP) inhibits whereas transfected PTHrP stimulates the proliferation of A10 aortic smooth muscle cells by nuclear translocation of the peptide. In the present studies, we asked whether these paradoxical trophic actions of PTHrP occur in smooth muscle cells (SMC) cultured from small intrarenal arteries of, and whether they are altered in, 12-wk-old spontaneously hypertensive rats (SHR) as compared to normotensive Wistar-Kyoto (WKY) rats. SHR cells grew faster than WKY cells. PTHrP transcript was increased in SHR-derived cells whereas PTH1 receptor (PTH1R) transcripts were similar in both cell lines. In both strains of cells, stable transfection with human PTHrP(1-139) cDNA did not further induce proliferation, suggesting maximal effect of endogenous PTHrP in wild cells. In contrast, transfection with antisense hPTHrP(1-139) cDNA, which abolished PTHrP mRNA, decreased WKY but increased SHR cell proliferation. Added PTHrP(1-36) (1-100 pM) decreased WKY and increased SHR cell proliferation. Additional studies indicated that the preferential coupling of PTH1-R to G-protein Gi was responsible for the proliferative effect of exogenous PTHrP in SHR cells. Moreover, PTHrP was detected in the nucleolus of a fraction of WKY and SHR renal SMC, in vitro as well as in situ, suggesting that the nucleolar translocation of PTHrP might be involved in the proliferative effects of endogenous PTHrP. In renovascular SMC, added PTHrP is antimitogenic, whereas endogenously produced PTHrP is mitogenic. These paradoxical effects of PTHrP on renovascular SMC proliferation appear to be reversed in the SHR model of genetic hypertension. A new concept emerges from these results, according to which a single molecule may have opposite effects on VSMC proliferation under physiological and pathophysiological conditions.

Parathyroid hormone-related protein in rat penis: expression, localization, and effect on cavernosal pressure

Although PTH-related protein-(1-36) [PTHrP-(1-36)] is known to be expressed in smooth muscle and to exert potent myorelaxant effects, its tonic effects on cavernosal smooth muscle has not yet been explored. Using the RT-PCR technique, the present study establishes that PTHrP messenger RNA is present in microdissected corpus cavernosa in the rat. In immunohistochemical studies using affinity-purified antibodies to middle regions of PTHrP, immunostaining was localized throughout the penile structures, including vessels, cavernosal smooth muscle, and trabecular fibroblasts. Strong immunostaining for PTHrP was also detected in the dorsal nerve bundles. In anesthetized rats, intracavernosally injected boluses of increasing doses of PTHrP-(1-36) (0.3-30 pmol in 100 microl saline) had little effect on intracavernosal pressure. However, they markedly potentiated the dilatory response to papaverine (8-800 nmol), increasing the papaverine-induced intracavernous pressure by 2.5-fold, close to the mean arterial pressure. In conclusion, the cavernosal expression of PTHrP messenger RNA, the distribution of immunoreactive PTHrP throughout the structuro-functional components of the erectile apparatus and its strong potentiating action on papaverine-induced cavernosal relaxation, collectively suggest that PTHrP participates in the control of cavernosal tone.

The role of the podocyte in glomerulosclerosis

Focal segmental glomerulosclerosis is a pathological hallmark of many forms of progressive renal disease. The 'classic' lesion, based on the adhesion of the capillary tuft to Bowman's capsule, results from the loss of podocytes from the capillary basement membrane. The recently described 'collapsing' variant, in contrast, has an apparent excess of extracapillary cells, which may represent dedifferentiated, 'dysregulated' podocytes.

Targeted overexpression of parathyroid hormone-related protein (PTHrP) to vascular smooth muscle in transgenic mice lowers blood pressure and alters vascular contractility

PTH-related protein (PTHrP) and its receptor are expressed in vascular smooth muscle cells and are believed to participate in the local regulation of vascular tone. To explore the function of locally produced PTHrP in vascular smooth muscle in vivo, we developed transgenic mice that overexpress PTHrP in smooth muscle using a smooth muscle alpha-actin promoter to direct expression of the transgene. In the PTHrP-overexpressing mice, messenger RNA expression was mainly restricted to smooth muscle-containing tissues. Several founders also expressed the transgene in bone and heart and exhibited striking abnormalities in the development of these tissues. In PTHrP-overexpressing mice, blood pressure was significantly lower than that in wild-type controls (121 +/- 3 vs. 135 +/- 2 mm Hg; P < 0.01). Moreover, the magnitude of the vasorelaxant response to iv infusions of PTHrP-(1-34)NH2 was significantly attenuated in the transgenic animals. A similar desensitization to PTHrP was observed in aortic ring and portal vein preparations. Surprisingly, PTHrP-overexpressing mice were also significantly less responsive to the hypotensive action of infused acetylcholine in vivo and to the relaxant actions of acetylcholine on aortic vessel preparations in vitro. In summary, we have successfully targeted overexpression of PTHrP to the smooth muscle of transgenic mice. When expressed in its normal autocrine/paracrine setting, PTHrP lowers systemic blood pressure and decreases vascular responsiveness to further relaxation by PTHrP and other endothelium-dependent vasorelaxants such as acetylcholine. We postulate that the heterologous desensitization to acetylcholine-induced relaxation in PTHrP-overexpressing blood vessels involves desensitization of second messenger/effector signaling pathways common to PTHrP and acetylcholine.

Expression and role of parathyroid hormone-related protein in human renal proximal tubule cells during recovery from ATP depletion

Parathyroid hormone (PTH)-related protein (PTHrP) is widely expressed in normal fetal and adult tissues and regulates growth and differentiation in a number of organ systems. Although various renal cell types produce PTHrP, and PTHrP expression in rat proximal renal tubules is upregulated in response to ischemic injury in vivo, the role of PTHrP in the kidney is unknown. To study the effects of injury on PTHrP expression and its consequences in more detail, the immortalized human proximal tubule cell line HK-2 was used in an in vitro model of ATP depletion to mimic in vivo renal ischemic injury. These cells secrete PTHrP into conditioned medium and express the type I PTH/PTHrP receptor. Treatment of confluent HK-2 cells for 2 h with substrate-free, glucose-free medium containing the mitochondrial inhibitor antimycin A (1 microM) resulted in 75% depletion of cellular ATP. After an additional 2 h in glucose-containing medium, cellular ATP levels recovered to approximately 75% of baseline levels. PTHrP mRNA levels, as measured in RNase protection assays, peaked at 2 h into the recovery period (at four times baseline expression). The increase in PTHrP mRNA expression was correlated with an increase in PTHrP protein content in HK-2 cells at 2 to 6 h into the recovery period. Heat shock protein-70 mRNA expression was not detectable under baseline conditions but likewise peaked at 2 h into the recovery period. Treatment of HK-2 cells during the recovery period after injury with an anti-PTHrP(1-36) antibody (at a dilution of 1:250) resulted in significant reductions in cell number and uptake of [3H]thymidine, compared with nonimmune serum at the same titer. Similar results were observed in uninjured HK-2 cells. It is concluded that this in vitro model of ATP depletion in a human proximal tubule cell line reproduces the pattern of gene expression previously observed in vivo in rat kidney after ischemic injury and that PTHrP plays a mitogenic role in the proliferative response after energy depletion.

Renal expression of parathyroid hormone-related protein (PTHrP) and PTH/PTHrP receptor in a rat model of tubulointerstitial damage

BACKGROUND

PTHrP, which appears to act as a growth/differentiation factor in a variety of tissues, is present in the kidney; however, its role is unclear.

METHODS

The expression of PTHrP and the PTH/PTHrP receptor were investigated by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in the remnant kidney of uninephrectomized (UNX) rats after protein overloading [1 g/day of bovine serum albumin (BSA)].

RESULTS

Compared with UNX-control rats, proteinuria in BSA-overloaded animals was detected within the first 24 hours and increased during the entire study period (28 days). Kidney examination by light microscopy showed no significant renal lesions at day 1 of BSA treatment, whereas at days 8 and 28, tubular lesions, infiltration of mononuclear cells, and mesangial expansion were observed. PTHrP mRNA expression in the renal cortex was already increased at day 1 (fourfold) and plateaued between days 8 and 28 (12- and 15-fold, respectively) in BSA-overloaded animals compared with UNX-control rats. At day 8, immunohistochemical analysis with two different anti-PTHrP antibodies showed a dramatic increase of PTHrP staining in the damaged proximal and distal tubules from BSA-overloaded rats with respect to UNX-control rats. Moreover, intense PTHrP immunostaining was also observed in glomerular mesangial and endothelial cells in BSA-overloaded rats, but not in the UNX-control rats. A reciprocal decrease of PTH/PTHrP receptor mRNA and immunostaining, without significant changes in the cellular localization (proximal and distal tubule, and glomerular mesangial and epithelial cells) of the PTH/PTHrP receptor positivity was found to occur in the renal cortex of BSA-overloaded rats. At day 8, coinciding with the up-regulation of PTHrP, an increase in the angiotensin converting enzyme and preproendothelin-1 gene expression was observed in the renal cortex of BSA-overloaded rats compared with UNX-control rats.

CONCLUSIONS

These results indicate that PTHrP can be added to the group of genes that are up-regulated in proximal tubular cells in response to intense proteinuria. Our results, together with previous findings, suggest that the vasoactive hormones angiotensin II and endothelin-1 could participate in the PTHrP production in the renal cortex of BSA-overloaded rats. Further experiments are required to clarify the mechanisms of PTHrP up-regulation and its possible role in the response to renal damage in this animal model.

Renovascular parathyroid hormone-related protein in spontaneously hypertensive rats: dilator or trophic factor?

Parathyroid hormone-related protein (PTHrP) is expressed throughout the renovascular system, and it dilates renal vessels, increases renal blood flow and glomerular filtration rate, and stimulates renin release. Mechanical forces and experimental hypertension have been shown to stimulate PTHrP expression in smooth muscles, suggesting a negative feedback control of vascular tone by PTHrP in hypertension. In this study, we compared the impact of a PTHrP receptor antagonist, PTHrP (7-34), and a PTHrP receptor agonist, PTHrP (1-36), on the vascular resistance of perfused kidneys isolated from spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). Endogenous PTHrP appears not to act as a renal vasodilator in either WKY or SHR. However, the vasodilation following infused PTHrP (1-36) is blunted markedly in SHR, possibly due to desensitization or down-regulation of PTH/PTHrP receptors. Negative feedback control of vascular tone by PTHrP in SHR thus appears unlikely. The results raise the question of whether endogenous renovascular PTHrP behaves rather as a growth factor than as a vasodilator.

AT2 antagonist-sensitive potentiation of angiotensin II-induced constriction by NO blockade and its dependence on endothelium and P450 eicosanoids in rat renal vasculature

1. We showed earlier that NO inhibition caused a left-shift and augmented Emax of the concentration-response curve of AT1-mediated (angiotensin II)-induced vasoconstrictions (AII-VC) in the rat kidney. The 0.01-0.1 nM AII-VC unmasked by the potentiating effect of NO inhibition, were sensitive not only to AT1 (L158809), but also to AT2 receptor (PD123319) antagonists. We now demonstrate the role of endothelium and eicosanoids in the NO-masked AT1/AT2-mediated component of the AII-VC in isolated indomethacin-perfused kidneys of the rat. 2. L-NAME increased 0.1 nM AII-VC 7.2 fold. Pretreatment of the kidneys with factor VIII antibody/complement or with the detergent CHAPS to damage endothelium, decreased carbachol-induced vasodilatation and blunted by 60 and 30% respectively, the enhancement of AII-VC during NO inhibition. 3. L-NAME also increased 3 microM noradrenaline (NA)-induced vasoconstriction (NA-VC) 8.1 fold. In contrast to AII-VC, endothelium damage was without effect on the enhancement of NA-VC by L-NAME, suggesting a dominant role of endothelium-derived NO in the enhancement of NA-VC. 4. During NO inhibition, ETYA (2 microM; an inhibitor of all arachidonic acid derived pathways) and alpha-naphtoflavone (10 microM; an inhibitor of the cytochrome P450 isozymes), decreased by 85% the 0.1 nM AII-VC. 5. In conclusion, during NO inhibition, the AT1-mediated constriction to low concentrations of AII, which is sensitive to AT2 antagonists, depends on intact endothelium, and can be blocked by inhibition of eicosanoid synthesis. The results suggest that the AII-mediated vasoconstriction through AT1 receptors is potentiated in the absence of NO, by the release of eicosanoids from the endothelium through AT2 receptors.

The physiology of parathyroid hormone-related protein: an emerging role as a developmental factor

Parathyroid hormone-related protein (PTHrP) is the agent responsible for humoral hypercalcemia of malignancy. Its pathogenic role in this syndrome is well established and attention has focused in recent years on the elucidation of the roles played by PTHrP in normal developmental and adult physiology. This review focuses on studies of the past two years: (a) elucidation of the posttranslational processing pattern of PTHrP, the mechanisms of action of the various secretory forms of PTHrP, the role of PTHrP as an intracrine regulator of cell growth and cell death; (b) the emergence of PTHrP as a critical developmental factor in the mammary gland, epidermis, and the skeleton; and (c) the advances in understanding of the roles of PTHrP in the regulation of pancreatic islet mass, vascular smooth muscle tone and proliferation, and materno-fetal calcium transfer across the placenta.

Cyclosporine increases renal parathyroid hormone-related protein expression in vivo in the rat

BACKGROUND

Clinical use of cyclosporine (CsA) is limited by its known nephrotoxicity. Parathyroid hormone (PTH)-related protein (PTHrP) increases after acute renal ischemia and stimulates proliferation of renal cells in culture. Herein, we have examined whether the renal expression of PTHrP and its PTH/PTHrP receptor is affected by chronic CsA nephrotoxicity.

METHODS

Rats were randomly assigned to receive daily intramuscular injections of either CsA (25 mg/kg) or the same volume of the vehicle olive oil (control) for 3 weeks. At this time interval, under ether anesthesia, rat blood and kidneys were obtained for analytical determinations, and total RNA isolation or immunohistochemistry, respectively.

RESULTS

Serum urea was 11+/-2 and 6+/-1 mmol/L (P < 0.01) in CsA-treated and control rats, respectively. We found that PTH/PTHrP receptor mRNA was unchanged, but PTHrP mRNA, and also transforming growth factor-beta1 mRNA expression as positive control, was about twofold increased in the kidney of CsA-treated rats. This was accompanied by increased PTHrP immunostaining in renal cortical tubules, associated with tubule vacuolation.

CONCLUSION

This study demonstrates an up-regulation of PTHrP, associated with chronic CsA-induced nephrotoxicity. Our findings support a role for PTHrP in the CsA-injured kidney.

Parathyroid hormone-related peptide--a smooth muscle tone and proliferation regulatory protein

Parathyroid hormone-related protein (PTHrP) appears to play crucial roles in the cardiovascular system. Over the past few years it has become apparent that there is more than one receptor recognizing parathyroid hormone or PTHrP, or both, and that PTHrP is not only a potent vasodilator of vascular smooth muscle cell tone, but is also a regulator of vascular smooth muscle cell proliferation and a secretagogue of renin and vasopressin. Investigators in several laboratories have started to query whether PTHrP intervenes in vascular diseases such as hypertension, (re)stenosis-atherosclerosis and endotoxaemia.

AT2-antagonist sensitive potentiation of angiotensin II-induced vasoconstrictions by blockade of nitric oxide synthesis in rat renal vasculature

1. Although the actions of angiotensin II (Ang II) on renal haemodynamics appear to be mediated by activation of the AT1 receptor subtype, AT2 binding sites have also been evidenced in the adult kidney vasculature. As NO is known to mask part of the renal effects of vasoconstrictor drugs, we queried whether the Ang II-induced vasoconstrictions could occur via multiple receptor subtypes during inhibition of NO synthesis. We explored the effect of AT1 and AT2 receptor (AT-R) antagonists on Ang II-induced pressure increases during NO synthase or soluble guanylyl cyclase inhibition in rat isolated kidneys perfused in the presence of indomethacin at constant flow in a single-pass circuit. 2. In the absence of NO blockade, the AT1-R antagonist L-158809 (500 nM) antagonized the Ang II-induced vasoconstrictions, while the AT2-R antagonist PD-123319 (500 nM) had no effect. 3. Perfusing kidneys in the presence of either NO synthase inhibitors, L-NAME (100 microM) or L-NOARG (1 mM), or soluble guanylyl cyclase inhibitor, LY-83583 (10 microM), significantly increased both molar pD2 (from 9.40+/-0.25 to 10.36+/-0.11) and Emax values (from 24.9+/-3.1 to 79.9+/-4.9 mmHg) of the concentration-response curve for Ang II-induced vasoconstriction. 4. In the presence of L-NAME, 500 nM L158809 abolished the Ang II-induced vasoconstrictions whatever the concentration tested. On the other hand, 500 nM PD-123319 reversed the left shift of the concentration-response curve for Ang II (molar pD2 value 9.72+/-0.13) leaving Emax value unaffected (91.3+/-7.6 mmHg). 5. In the presence of L-NAME, the potentiated vasoconstriction induced by 0.1 nM and the augmented vasoconstriction induced by 10 nM Ang II were fully inhibited in a concentration-dependent manner by L-158809 (0.05-500 nM). By contrast, PD-123319 (0.5-500 nM) did not affect the 10 nM Ang II-induced vasoconstriction and concentration-dependently decreased the 0.1 nM Ang II-induced vasoconstriction plateauing at 65% inhibition above 5 nM antagonist. 6. Similar to PD-123319, during NO blockade the AT2-R antagonist CGP-42112A at 5 nM decreased by 50% the 0.1 nM Ang II-induced vasoconstriction and at 500 nM had no effect on 10 nM Ang II-induced vasoconstriction. 7. In conclusion, the renal Ang II-induced vasoconstriction, which is antagonized only by AT1-R antagonist in the presence of endogenous NO, becomes sensitive to both AT1- and AT2-R antagonists during NO synthesis inhibition. While AT1-R antagonist inhibited both L-NAME-potentiated and -augmented components of Ang II-induced vasoconstriction, AT2-R antagonists inhibited only the L-NAME-potentiated component.

Hemodynamic effects of parathyroid hormone-related peptide-(1-34) in humans

It has been suggested that PTH-related peptide-(1-34) (PTHrP) is a regulator or modulator of regional or systemic cardiovascular function with varying vasodilating actions in different species. We have studied the cardiovascular pharmacodynamic profile of PTHrP in healthy humans. In a double blind, placebo-controlled, cross-over study design, eight healthy subjects were assigned to stepwise increased i.v. doses of PTHrP. In addition, a dose-response curve to PTHrP was constructed in a dorsal hand vein in eight subjects. PTHrP dose-dependently increased pulse rate and renal plasma flow by more than 50% (P < 0.0001 for both parameters, by ANOVA), but only a small venodilating response was seen in hand vein experiments, and no effect was noted on mean arterial blood pressure or cardiac inotropic performance. Although it is unlikely that PTHrP regulates systemic hemodynamics, its chronotropic effect and its potent action on renal plasma flow may represent the primary cardiovascular physiological targets of action.