Regulation of Na,K-ATPase expression by endothelin-1 in transformed human ciliary non-pigmented epithelial (HNPE) cells

Role of Translationally Controlled Tumor Protein (TCTP) in the Development of Hypertension and Related Diseases in Mouse Models

Translationally controlled tumor protein (TCTP) is a multifunctional protein that plays a wide variety of physiological and pathological roles, including as a cytoplasmic repressor of Na,K-ATPase, an enzyme pivotal in maintaining Na+ and K+ ion gradients across the plasma membrane, by binding to and inhibiting Na,K-ATPase. Studies with transgenic mice overexpressing TCTP (TCTP-TG) revealed the pathophysiological significance of TCTP in the development of systemic arterial hypertension. Overexpression of TCTP and inhibition of Na,K-ATPase result in the elevation of cytoplasmic Ca2+ levels, which increases the vascular contractility in the mice, leading to hypertension. Furthermore, studies using an animal model constructed by multiple mating of TCTP-TG with apolipoprotein E knockout mice (ApoE KO) indicated that TCTP-induced hypertension facilitates the severity of atherosclerotic lesions in vivo. This review attempts to discuss the mechanisms underlying TCTP-induced hypertension and related diseases gleaned from studies using genetically altered animal models and the potential of TCTP as a target in the therapy of hypertension-related pathological conditions.

Hypertension resulting from overexpression of translationally controlled tumor protein increases the severity of atherosclerosis in apolipoprotein E knock-out mice

Hypertension is a well-established etiological factor for atherogenesis. We previously showed that transgenic mice overexpressing translationally controlled tumor protein (TCTP) develop systemic arterial hypertension. In this study we explored the cardiovascular effects of TCTP overexpression and possibly of the resultant hypertension on the severity of atherosclerosis in apolipoprotein E-deficient mice. Through multiple mating of TCTP-overexpressing transgenic mice (TCTP-TG) with apolipoprotein E knock-out mice (ApoE KO), we generated non-transgenic (nTG), TCTP-TG, nTG/ApoE KO and TCTP-TG/ApoE KO mice with similar genetic background. Male mice, 7-week old, were fed a lipid-enriched Western diet for 16 weeks, and blood pressure and body weight change were monitored every 2 weeks. Plasma lipid profiles and atherosclerotic lesions in aorta were quantified at the end of study. We found that blood pressure levels of TCTP-TG and TCTP-TG/ApoE KO, were similarly elevated while nTG and nTG/ApoE KO mice were normotensive. TCTP overexpression in ApoE KO mice led to significant exacerbation of atherosclerotic lesions. Feeding Western diet resulted in increases in total cholesterol, triglyceride (TG) and low density lipoprotein, and decreased high density lipoprotein (HDL) in ApoE KO mice. No significant differences were found in plasma lipid profiles of nTG/ApoE KO and TCTP-TG/ApoE KO. This study suggests that overexpression of TCTP, which induces hypertension, also accelerates the development of atherosclerotic lesion caused by high-fat and high-cholesterol diet without significantly altering plasma lipid profiles. We conclude that TCTP-induced hypertension could increase the severity of atherosclerotic lesion and suggest that inhibition of TCTP or its signaling pathways may be a potential approach to the therapy of both diseases, hypertension and atherosclerosis.

The effect of endothelin-1 on Src-family tyrosine kinases and Na,K-ATPase activity in porcine lens epithelium

Previous studies show Src family kinase (SFK) activation is involved in a response that stimulates Na,K-ATPase. Here, we tested whether SFK activation is involved in the Na,K-ATPase response to endothelin-1 (ET-1). Intact porcine lenses were exposed to 100 nM ET-1 for 5-30 min. Then, the epithelium was removed and used for Na,K-ATPase activity measurement and Western blot analysis of SFK activation. Na,K-ATPase activity was reduced by ∼30% in lenses exposed to ET-1 for 15 min. The response was abolished by the SFK inhibitor PP2 or the ET receptor antagonist, PD145065. Activation of a ∼61 kDa SFK was evident from an increase in Y416 phosphorylation, which reached a maximum at 15 min ET-1 treatment, and a decrease in Y527 phosphorylation. PP2 prevented SFK activation. Since Fyn, Src, Hck, and Yes may contribute to the observed 61 kDa band, these SFKs were isolated by immunoprecipitation and analyzed. Based on Y416 phosphorylation, ET-1 appeared to activate Fyn, while Src and Hck were inhibited and Yes was unaltered. ET-1 requires SFK activation to cause Na,K-ATPase inhibition. ET-1 elicits a different pattern of SFK activation from that reported earlier for purinergic agonists that stimulate Na,K-ATPase activity and activate Src. In the ET-1 response Src is inhibited and Fyn is activated. The findings suggest SFK phosphorylation is involved in a regulatory mechanism for Na,K-ATPase. Knowing this may help us understand drug actions on Na,K-ATPase. Faulty regulation of Na,K-ATPase in the lens could contribute to cataract formation since an abnormal sodium content is associated with lens opacification.

Capillary endothelial Na(+), K(+), ATPase transporter homeostasis and a new theory for migraine pathophysiology

BACKGROUND

Cerebrospinal fluid sodium concentration ([Na(+)](csf)) increases during migraine, but the cause of the increase is not known.

OBJECTIVE

Analyze biochemical pathways that influence [Na(+)](csf) to identify mechanisms that are consistent with migraine.

METHOD

We reviewed sodium physiology and biochemistry publications for links to migraine and pain.

RESULTS

Increased capillary endothelial cell (CEC) Na(+), K(+), -ATPase transporter (NKAT) activity is probably the primary cause of increased [Na(+)](csf). Physiological fluctuations of all NKAT regulators in blood, many known to be involved in migraine, are monitored by receptors on the luminal wall of brain CECs; signals are then transduced to their abluminal NKATs that alter brain extracellular sodium ([Na(+)](e)) and potassium ([K(+)](e)).

CONCLUSIONS

We propose a theoretical mechanism for aura and migraine when NKAT activity shifts outside normal limits: (1) CEC NKAT activity below a lower limit increases [K(+)](e), facilitates cortical spreading depression, and causes aura; (2) CEC NKAT activity above an upper limit elevates [Na(+)](e), increases neuronal excitability, and causes migraine; (3) migraine-without-aura may arise from CEC NKAT over-activity without requiring a prior decrease in activity and its consequent spreading depression; (4) migraine triggers disturb, and treatments improve, CEC NKAT homeostasis; (5) CEC NKAT-induced regulation of neural and vasomotor excitability coordinates vascular and neuronal activities, and includes occasional pathology from CEC NKAT-induced apoptosis or cerebral infarction.

Role of the ETB receptor in retinal ganglion cell death in glaucoma

Recent observations suggest that the vasoactive peptide endothelin-1 (ET-1) may be an important contributor to the etiology of glaucoma. ET-1 administration has been shown to produce optic nerve axonal loss and apoptosis of retinal ganglion cells. Ocular ET-1 levels are elevated in aqueous humor in response to elevated intraocular pressure both in glaucoma patients and in animal models of glaucoma; however, the precise mechanisms by which ET-1 mediates glaucomatous optic neuropathy are not clear. Presently we report that ET-1-mediated apoptosis was markedly attenuated in ETB receptor-deficient rats, suggesting a key role for ETB receptors in apoptosis of retinal ganglion cells by ET-1 treatment. Using virally transformed rat retinal ganglion cells (RGC-5 cells), we found that ET-1 (100 nmol/L) treatment produced apoptotic changes in these cells that was determined by flow cytometric analyses, release of mitochondrial cytochrome c to the cytosol, and increased phosphorylation of c-Jun N-terminal kinase. Pretreatment with the ETB-receptor antagonist BQ788 (1 micromol/L) was able to significantly attenuate ET-1-mediated apoptosis in RGC-5 cells. ET-1-mediated apoptotic changes in RGC-5 cells were associated with ETB-receptor activation and were accompanied by a significant upregulation of ETB-receptor expression. These studies suggest that ocular ET-1 acts through ETB receptors to mediate apoptosis of retinal ganglion cells, a key event in glaucoma and related optic neuropathies.