Extracellular NAD+ regulates intracellular calcium levels and induces activation of human granulocytes

Transient electric changes immediately after surgical trauma

CONTEXT

Electric stimulation is frequently used to promote soft tissue healing, although we do not have a complete understanding of the tissue's electromagnetic properties.

OBJECTIVE

To measure the transient electric changes in skin and muscle tissue immediately after trauma.

DESIGN

1-group time series.

SETTING

Climate-controlled operating room in a public urban hospital.

PATIENTS OR OTHER PARTICIPANTS

Eleven participants (8 females, 3 males) with a mean age of 65.18 +/- 11.36 years undergoing total hip arthroplasty.

INTERVENTION(S)

An incision approximately 10 cm distal to the posterior superior iliac spine extended distally over the greater trochanter and along the lateral limb. The incision was completed in 2 cuts: (1) skin and subcutaneous fat and (2) muscle tissue.

MAIN OUTCOME MEASURE(S)

Three measurement sessions were performed with an electrometer before and after a skin incision and after a muscle incision. Potential differences and current intensity were measured immediately after acute trauma to determine the transient electric changes associated with soft tissue injury.

RESULTS

The electric potentials were significantly more negative after the skin incision (P = .036) and skin plus muscle incision (P = .008; preincision = 0.001 +/- 0.015 V, skin incision = -0.127 +/- 0.134 V, skin plus muscle incision = -0.192 +/- 0.153 V). Current intensity changed significantly after the skin plus muscle incision (P = .008; preincision = 0.046 +/- 0.112 pA, skin incision = -0.803 +/- 0.904 pA, skin plus muscle incision = -1.708 +/- 1.302 pA).

CONCLUSIONS

Soft tissue trauma generated negative transient electric changes.

NAADP+ is an agonist of the human P2Y11 purinergic receptor

Nicotinic acid adenine dinucleotide phosphate (NAADP+) is an intracellular second messenger releasing Ca2+ from intracellular stores in different cell types. In addition, it is also active in triggering [Ca2+](i) increase when applied extracellularly and various underlying mechanisms have been proposed. Here, we used hP2Y(11)-transfected 1321N1 astrocytoma cells to unequivocally establish whether extracellular NAADP+ is an agonist of the P2Y(11) receptor, as previously reported for beta-NAD+ [I. Moreschi, S. Bruzzone, R.A. Nicholas, et al., Extracellular NAD+ is an agonist of the human P2Y11 purinergic receptor in human granulocytes, J. Biol. Chem. 281 (2006) 31419-31429]. Extracellular NAADP+ triggered a concentration-dependent two-step elevation of [Ca2+](i) in 1321N1-hP2Y(11) cells, but not in wild-type 1321N1 cells, secondary to the intracellular production of IP(3), cAMP and cyclic ADP-ribose (cADPR). Specifically, the transient [Ca2+](i) rise proved to be related to IP(3) overproduction and to consequent Ca2+ mobilization, while the sustained [Ca2+](i) elevation was caused by the cAMP/ADP-ribosyl cyclase (ADPRC)/cADPR signalling cascade and by influx of extracellular Ca2+. In human granulocytes, endogenous P2Y(11) proved to be responsible for the NAADP+-induced cell activation (as demonstrated by the use of NF157, a selective and potent inhibitor of P2Y(11)), unveiling a role of NAADP+ as a pro-inflammatory cytokine. In conclusion, we provide unequivocal evidence for the activation of a member of the P2Y receptor subfamily by NAADP+.

Emerging functions of extracellular pyridine nucleotides

In addition to the well-known metabolic functions of NAD and NADP, it is rapidly emerging that these 2 pyridine nucleotides and their derivatives also play important roles in cell signaling. Surprisingly, a number of NAD(P) metabolizing enzymes and NAD(P) targets have been found on the outer surface of the plasma membrane and the presence of NAD has been confirmed in extracellular fluids. These findings have opened the door to a new field of research aimed at elucidating the contribution of extracellular pyridine nucleotides in physiological signaling pathways and pathological conditions.

Abscisic acid is an endogenous cytokine in human granulocytes with cyclic ADP-ribose as second messenger

Abscisic acid (ABA) is a phytohormone involved in fundamental physiological processes of higher plants, such as response to abiotic stress (temperature, light, drought), regulation of seed dormancy and germination, and control of stomatal closure. Here, we provide evidence that ABA stimulates several functional activities [phagocytosis, reactive oxygen species and nitric oxide (NO) production, and chemotaxis] of human granulocytes through a signaling pathway sequentially involving a pertussis toxin (PTX)-sensitive G protein/receptor complex, protein kinase A activation, ADP-ribosyl cyclase phosphorylation, and consequent cyclic-ADP-ribose overproduction, leading to an increase of the intracellular Ca(2+) concentration. The increase of free intracellular ABA and its release by activated human granulocytes indicate that ABA should be considered as a new pro-inflammatory cytokine in humans. This discovery is an intriguing example of conservation of a hormone and its signaling pathway from plants to humans and provides insight into the molecular mechanisms of granulocyte activation, possibly leading to the development of new antiinflammatory drugs.

Emerging functions of extracellular pyridine nucleotides

In addition to the well-known metabolic functions of NAD and NADP, it is rapidly emerging that these 2 pyridine nucleotides and their derivatives also play important roles in cell signaling. Surprisingly, a number of NAD(P) metabolizing enzymes and NAD(P) targets have been found on the outer surface of the plasma membrane and the presence of NAD has been confirmed in extracellular fluids. These findings have opened the door to a new field of research aimed at elucidating the contribution of extracellular pyridine nucleotides in physiological signaling pathways and pathological conditions.

Cyclic ADP-ribose is a second messenger in the lipopolysaccharide-stimulated activation of murine N9 microglial cell line

Lipopolysaccharide, the main component of the cell wall of Gram-negative bacteria, is known to activate microglial cells following its interaction with the CD14/Toll-like receptor complex (TLR-4). The activation pathway triggered by lipopolysaccharide in microglia involves enhanced basal levels of intracellular calcium ([Ca2+]i) and terminates with increased generation of cytokines/chemokines and nitric oxide. Here we demonstrate that in lipopolysaccharide-stimulated murine N9 microglial cells, cyclic ADP-ribose, a universal and potent Ca2+ mobiliser generated from NAD+ by ADP-ribosyl cyclases (ADPRC), behaves as a second messenger in the cell activation pathway. Lipopolysaccharide induced phosphorylation, mediated by multiple protein kinases, of the mammalian ADPRC CD38, which resulted in significantly enhanced ADPRC activity and in a 1.7-fold increase in the concentration of intracellular cyclic ADP-ribose. This event was paralleled by doubling of the basal [Ca2+]i levels, which was largely prevented by the cyclic ADP-ribose antagonists 8-Br-cyclic ADP-ribose and ryanodine (by 75% and 88%, respectively). Both antagonists inhibited, although incompletely, functional events downstream of the lipopolysaccharide-induced microglia-activating pathway, i.e. expression of inducible nitric oxide synthase, overproduction and release of nitric oxide and of tumor necrosis factor alpha. The identification of cyclic ADP-ribose as a key signal metabolite in the complex cascade of events triggered by lipopolysaccharide and eventually leading to enhanced generation of pro-inflammatory molecules may suggest a new therapeutic target for treatment of neurodegenerative diseases related to microglia activation.

Extracellular NAD+ is an agonist of the human P2Y11 purinergic receptor in human granulocytes

Micromolar concentrations of extracellular beta-NAD+ (NAD(e)+) activate human granulocytes (superoxide and NO generation and chemotaxis) by triggering: (i) overproduction of cAMP, (ii) activation of protein kinase A, (iii) stimulation of ADP-ribosyl cyclase and overproduction of cyclic ADP-ribose (cADPR), a universal Ca2+ mobilizer, and (iv) influx of extracellular Ca2+. Here we demonstrate that exposure of granulocytes to millimolar rather than to micromolar NAD(e)+ generates both inositol 1,4,5-trisphosphate (IP3) and cAMP, with a two-step elevation of intracellular calcium levels ([Ca2+]i): a rapid, IP3-mediated Ca2+ release, followed by a sustained influx of extracellular Ca2+ mediated by cADPR. Suramin, an inhibitor of P2Y receptors, abrogated NAD(e)+-induced intracellular increases of IP3, cAMP, cADPR, and [Ca2+]i, suggesting a role for a P2Y receptor coupled to both phospholipase C and adenylyl cyclase. The P2Y(11) receptor is the only known member of the P2Y receptor subfamily coupled to both phospholipase C and adenylyl cyclase. Therefore, we performed experiments on hP2Y(11)-transfected 1321N1 astrocytoma cells: micromolar NAD(e)+ promoted a two-step elevation of the [Ca2+]i due to the enhanced intracellular production of IP3, cAMP, and cADPR in 1321N1-hP2Y(11) but not in untransfected 1321N1 cells. In human granulocytes NF157, a selective and potent inhibitor of P2Y(11), and the down-regulation of P2Y(11) expression by short interference RNA prevented NAD(e)+-induced intracellular increases of [Ca2+]i and chemotaxis. These results demonstrate that beta-NAD(e)+ is an agonist of the P2Y(11) purinoceptor and that P2Y(11) is the endogenous receptor in granulocytes mediating the sustained [Ca2+]i increase responsible for their functional activation.