Role of Ca2+-dependent and Ca2+-sensitive mechanisms in sphingosine 1-phosphate-induced constriction of isolated porcine retinal arterioles in vitro

Sphingolipid metabolism and signaling in cardiovascular diseases

Sphingolipids are a structural component of the cell membrane, derived from sphingosine, an amino alcohol. Its sphingoid base undergoes various types of enzymatic transformations that lead to the formation of biologically active compounds, which play a crucial role in the essential pathways of cellular signaling, proliferation, maturation, and death. The constantly growing number of experimental and clinical studies emphasizes the pivotal role of sphingolipids in the pathophysiology of cardiovascular diseases, including, in particular, ischemic heart disease, hypertension, heart failure, and stroke. It has also been proven that altering the sphingolipid metabolism has cardioprotective properties in cardiac pathologies, including myocardial infarction. Recent studies suggest that selected sphingolipids may serve as valuable biomarkers useful in the prognosis of cardiovascular disorders in clinical practice. This review aims to provide an overview of the current knowledge of sphingolipid metabolism and signaling in cardiovascular diseases.

Sphingosine-1-phosphate in mitochondrial function and metabolic diseases

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite. The past decade has witnessed exponential growth in the field of S1P research, partly attributed to drugs targeting its receptors or kinases. Accumulating evidence indicates that changes in the S1P axis (i.e., S1P production, transport, and receptors) may modify metabolism and eventually mediate metabolic diseases. Dysfunction of the mitochondria on a master monitor of cellular metabolism is considered the leading cause of metabolic diseases, with aberrations typically induced by abnormal biogenesis, respiratory chain complex disorders, reactive oxygen species overproduction, calcium deposition, and mitophagy impairment. Accordingly, we discuss decades of investigation into changes in the S1P axis and how it controls mitochondrial function. Furthermore, we summarize recent scientific advances in disorders associated with the S1P axis and their involvement in the pathogenesis of metabolic diseases in humans, including type 2 diabetes mellitus and cardiovascular disease, from the perspective of mitochondrial function. Finally, we review potential challenges and prospects for S1P axis application to the regulation of mitochondrial function and metabolic diseases; these data may provide theoretical guidance for the treatment of metabolic diseases.

Hydrogen sulfide dilates the isolated retinal artery mainly via the activation of myosin phosphatase

AIMS

Hydrogen sulfide (H₂S) is shown in ocular tissues and suggested to involve in the regulation of retinal circulation. However, the mechanism of H₂S-induced relaxation on retinal artery is not clarified yet. Herein, we aimed to evaluate the role of several calcium (Ca²⁺) signaling and Ca²⁺ sensitization mechanisms in the relaxing effect of H₂S donor, NaHS, on retinal arteries.

MATERIALS AND METHODS

Relaxing effects of NaHS (10^-5-3 × 10^-3M) were determined on precontracted retinal arteries in Ca²⁺ free medium as well as in the presence of the inhibitors of Ca²⁺ signaling and Ca²⁺ sensitization mechanisms. Additively, Ca²⁺ sensitivity of the contractile apparatus were evaluated by CaCl₂-induced contractions in the presence of NaHS (3 × 10^-3M). Functional experiments were furtherly assessed by protein and/or mRNA expressions, as appropriate.

KEY FINDINGS

The relaxations to NaHS were preserved in Ca²⁺ free medium while NaHS pretreatment decreased the responsiveness to CaCl₂. The inhibitors of plasmalemmal Ca²⁺-ATPase, sarcoplasmic-endoplasmic reticulum Ca²⁺-ATPase, Na⁺-Ca²⁺ ion-exchanger and myosin light chain kinase (MLCK) unchanged the relaxations to NaHS. Likewise, Ca²⁺ sensitization mechanisms including, rho kinase, protein kinase C and tyrosine kinase were unlikely to mediate the relaxation to NaHS in retinal artery. Whereas, a marked reduction was determined in NaHS-induced relaxations in the presence of MLCP inhibitor, calyculin A. Supportively, NaHS pretreatment significantly reduced phosphorylation of MYPT1-subunit of MLCP.

SIGNIFICANCE

The relaxing effect of NaHS in retinal artery is likely to be related to the activation of MLCP and partly, to decrement in Ca²⁺ sensitivity of contractile apparatus.

The effects of phospholipase C on oestradiol and progesterone secretion in porcine granulosa cells cultured in vitro

Granulosa cells play important roles in the regulation of ovarian functions. Phospholipase C is crucial in several signalling pathways and could participate in the molecular mechanisms of cell proliferation, differentiation and ageing. The objective of this study was to identify the effects of phospholipase C on the steroidogenesis of oestradiol and progesterone in porcine granulosa cells cultured in vitro. Inhibitor U73122 or activator m-3M3FBS of phospholipase C was added to the in vitro medium of porcine granulosa cells, respectively. The secretion of oestradiol decreased after 2 hr, 8 hr, 12 hr, 24 hr and 48 hr of treatment with 500 nM U73122 (p < .05) and decreased after 2 hr of treatment in the 500 nM m-3M3FBS addition group (p < .05). The secretion of progesterone increased after 4 hr of treatment with 500 nM U73122 (p < .05) and increased after 2 hr and 8 hr of treatment in the 500 nM m-3M3FBS addition group (p < .05). The ratio of oestradiol to progesterone decreased at each time point, except 8 hr after the addition of 500 nM U73122 (p < .05). The ratio of oestradiol to progesterone decreased after 2 hr (p < .05) of treatment with 500 nM m-3M3FBS. In genes that regulate the synthesis of oestradiol or progesterone, the mRNA expression of CYP11A1 was markedly increased (p < .05), and the mRNA expression of other genes did not change significantly in the U73122 treatment group, while the addition of m-3M3FBS did not change those genes significantly despite the contrary trend. Our results demonstrated that phospholipase C can be a potential target to stimulate the secretion of oestradiol and suppress progesterone secretion in porcine granulosa cells cultured in vitro, which shed light on a novel biological function of phospholipase C in porcine granulosa cells.

The effect of sphingosine-1-phosphate on colonic smooth muscle contractility: Modulation by TNBS-induced colitis

Aim

Increased levels of circulating sphingosine-1-phosphate (S1P) have been reported in ulcerative colitis. The objective of this study was to examine the effect of S1P on colonic smooth muscle contractility and how is it affected by colitis.

Methods

Colonic inflammation was induced by intrarectal administration of trinitrobenzene sulfonic acid. Five days later colon segments were isolated and used for contractility experiments and immunoblotting.

Results

S1P contracted control and inflamed colon segments and the contraction was significantly greater in inflamed colon segments. S1P-induced contraction was mediated by S1PR1 and S1PR2 in control and S1PR2 in inflamed colon segments. S1PR3 did not play a significant role in S1P-induced contractions in control or inflamed colon. S1PR1, S1PR2 and S1PR3 proteins were expressed in colon segments from both groups. The expression of S1PR1 and S1PR2 was significantly enhanced in control and inflamed colon segments, respectively. S1PR3 levels however were not significantly different between the two groups. Nifedipine significantly reduced S1P-induced contraction in control but not inflamed colon segments. Thapsigargin significantly reduced S1P-induced contraction of the inflamed colon. GF 109203X and Y-27632, alone abolished S1P-induced contraction of the control but not inflamed colon segments. Combination of GF 109203X, Y-27632 and thapsigargin abolished S1P-induced contraction of inflamed colon segments.

Conclusion

S1P contracted control colon via S1PR1 and S1PR2 and inflamed colon exclusively via S1PR2. Calcium influx (control) or release (inflamed) and calcium sensitization are involved in S1P-induced contraction. Exacerbated response to S1P in colitic colon segments may explain altered colonic motility reported in patients and experimental models of inflammatory bowel disease.

Dihydroartemisinin counteracts fibrotic portal hypertension via farnesoid X receptor-dependent inhibition of hepatic stellate cell contraction

Portal hypertension is a frequent pathological symptom occurring especially in hepatic fibrosis and cirrhosis. Current paradigms indicate that inhibition of hepatic stellate cell (HSC) activation and contraction is anticipated to be an attractive therapeutic strategy, because activated HSC dominantly facilitates an increase in intrahepatic vein pressure through secreting extracellular matrix and contracting. Our previous in vitro study indicated that dihydroartemisinin (DHA) inhibited contractility of cultured HSC by activating intracellular farnesoid X receptor (FXR). However, the effect of DHA on fibrosis-related portal hypertension still requires clarification. In this study, gain- and loss-of-function models of FXR in HSC were established to investigate the mechanisms underlying DHA protection against chronic CCl₄ -caused hepatic fibrosis and portal hypertension. Immunofluorescence staining visually showed a decrease in FXR expression in CCl₄ -administrated rat HSC but an increase in that in DHA-treated rat HSC. Serum diagnostics and morphological analyses consistently indicated that DHA exhibited hepatoprotective effects on CCl₄ -induced liver injury. DHA also reduced CCl₄ -caused inflammatory mediator expression and inflammatory cell infiltration. These improvements were further enhanced by INT-747 but weakened by Z-guggulsterone. Noteworthily, DHA, analogous to INT-747, significantly lowered portal vein pressure and suppressed fibrogenesis. Experiments on mice using FXR shRNA lentivirus consolidated the results above. Mechanistically, inhibition of HSC activation and contraction was found as a cellular basis for DHA to relieve portal hypertension. These findings demonstrated that DHA attenuated portal hypertension in fibrotic rodents possibly by targeting HSC contraction via a FXR activation-dependent mechanism. FXR could be a target molecule for reducing portal hypertension during hepatic fibrosis.

Sphingolipid De Novo Biosynthesis: A Rheostat of Cardiovascular Homeostasis

Sphingolipids (SL) are both fundamental structural components of the eukaryotic membranes and signaling molecules that regulate a variety of biological functions. The highly-bioactive lipids, ceramide and sphingosine-1-phosphate, have emerged as important regulators of cardiovascular function in health and disease. In this review we discuss recent insights into the role of SLs, particularly ceramide and sphingosine-1-phosphate, in the pathophysiology of the cardiovascular system. We also highlight advances into the molecular mechanisms regulating serine palmitoyltransferase, the first and rate-limiting enzyme of de novo SL biosynthesis, with an emphasis on the recently discovered inhibitors of serine palmitoyltransferase, ORMDL and NOGO-B proteins. Understanding the molecular mechanisms regulating this biosynthetic pathway may lead to the development of novel therapeutic approaches for the treatment of cardiovascular diseases.

S1P Signaling and De Novo Biosynthesis in Blood Pressure Homeostasis

Initially discovered as abundant components of eukaryotic cell membranes, sphingolipids are now recognized as important bioactive signaling molecules that modulate a variety of cellular functions, including those relevant to cancer and immunologic, inflammatory, and cardiovascular disorders. In this review, we discuss recent advances in our understanding of the role of sphingosine-1-phosphate (S1P) receptors in the regulation of vascular function, and focus on how de novo biosynthesized sphingolipids play a role in blood pressure homeostasis. The therapeutic potential of new drugs that target S1P signaling is also discussed.

Overview of Antagonists Used for Determining the Mechanisms of Action Employed by Potential Vasodilators with Their Suggested Signaling Pathways

This paper is a review on the types of antagonists and the signaling mechanism pathways that have been used to determine the mechanisms of action employed for vasodilation by test compounds. Thus, we exhaustively reviewed and analyzed reports related to this topic published in PubMed between the years of 2010 till 2015. The aim of this paperis to suggest the most appropriate type of antagonists that correspond to receptors that would be involved during the mechanistic studies, as well as the latest signaling pathways trends that are being studied in order to determine the route(s) that atest compound employs for inducing vasodilation. The methods to perform the mechanism studies were included. Fundamentally, the affinity, specificity and selectivity of the antagonists to their receptors or enzymes were clearly elaborated as well as the solubility and reversibility. All the signaling pathways on the mechanisms of action involved in the vascular tone regulation have been well described in previous review articles. However, the most appropriate antagonists that should be utilized have never been suggested and elaborated before, hence the reason for this review.