Perturbed bone composition and integrity with disorganized osteoblast function in zinc receptor/Gpr39-deficient mice

The pathophysiological functions and therapeutic potential of GPR39: Focus on agonists and antagonists

G protein-coupled receptor 39 (GPR39), a member of the growth hormone-releasing peptide family, exhibits widespread expression across various tissues and demonstrates high constitutive activity, primarily activated by zinc ions. It plays critical roles in cell proliferation, differentiation, survival, apoptosis, and ion transport through the recruitment of Gq/11, Gs, G12/13, and β-arrestin proteins. GPR39 is involved in anti-inflammatory and antioxidant responses, highlighting its diverse pathophysiological functions. Recent discoveries of endogenous ligands have enhanced our understanding of GPR39's physiological roles. Aberrant expression and reactivation of GPR39 have been implicated in a range of diseases, particularly central nervous system disorders, endocrine disruptions, cardiovascular diseases, cancers, and liver conditions. These findings position GPR39 as a promising therapeutic target, with the efficacy of synthetic ligands validated in various in vivo models. Nonetheless, their clinical applicability remains uncertain, necessitating further exploration of novel agonists-especially biased agonists-and antagonists. This review examines the unique residues contributing to the high constitutive activity of GPR39, its endogenous and synthetic ligands, and its pathophysiological implications, aiming to elucidate its pharmacological potential for clinical application in disease treatment.

Multifunctional Bionic Periosteum with Ion Sustained-Release for Bone Regeneration

In this study, a novel bionic periosteum (BP)-bioactive glass fiber membrane (BGFM) is designed. The introduction of magnesium ion (Mg2+) and zinc ion (Zn2+) change the phase separation during the electrospinning (ES) jet stretching process. The fiber's pore structure transitions from connected to closed pores, resulting in a decrease in the rapid release of metal ions while also improving degradation via reducing filling quality. Additionally, the introduction of magnesium (Mg) and zinc (Zn) lead to the formation of negative charged tetrahedral units (MgO4 2- and ZnO4 2-) in the glass network. These units effectively trap positive charged metal ions, further inhibiting ion release. In vitro experiments reveal that the deigned bionic periosteum regulates the polarization of macrophages toward M2 type, thereby establishing a conducive immune environment for osteogenic differentiation. Bioinformatics analysis indicate that BP enhanced bone repair via the JAK-STAT signaling pathway. The slow release of metal ions from the bionic periosteum can directly enhance osteogenic differentiation and vascularization, thereby accelerating bone regeneration. Finally, the bionic periosteum exhibits remarkable capabilities in angiogenesis and osteogenesis, demonstrating its potential for bone repair in a rat calvarial defect model.

Severe Zinc Deficiency Impairs Accrual of Bone in Rapidly Growing Rats That Is Partially Corrected Following Short-term Zinc Repletion

Zinc (Zn) deficiency impairs bone growth. However, the precise skeletal effects of varying levels of Zn deficiency and response to subsequent Zn repletion on the growing skeleton are incompletely understood. To address this gap in knowledge, we investigated the effects of dietary Zn ((severe deficiency (< 0.5 mg Zn/kg diet) and short-term Zn repletion (30 mg/kg diet), marginal deficiency (6 mg Zn/kg diet)) on bone mass, density, and cortical and cancellous bone microarchitecture in growing male Sprague Dawley rats. Marginal Zn intake for 42 days had no effect on bone mass or cortical and cancellous bone microarchitecture. Twenty-one days of severe Zn deficiency lowered serum osteocalcin and C terminal telopeptide of type I collagen (CTX-1), decreased tibial bone mineral content and density, and lowered cross-sectional volume, cortical volume, and cortical thickness in tibial diaphysis as compared to both Zn-adequate (30 mg/kg diet) and pair-fed controls. Severe Zn deficiency similarly lowered cancellous bone volume in proximal tibial metaphysis. Zn repletion (10 days) accelerated weight gain, indicative of catch-up growth, normalized CTX-1 and osteocalcin, but did not normalize bone mass (unadjusted and adjusted for body weight) or cortical and cancellous bone microarchitecture. In summary, severe but not marginal Zn deficiency in rapidly growing rats impaired acquisition of cortical and cancellous bone, resulting in abnormalities in bone microarchitecture. Zn repletion accelerated weight gain compared to Zn-adequate controls but absence of a compensatory increase in serum osteocalcin or bone mass suggests Zn repletion may be insufficient to fully counteract the detrimental effects of prior Zn deficiency on skeletal growth.

Functions of the Zinc-Sensing Receptor GPR39 in Regulating Intestinal Health in Animals

G protein-coupled receptor 39 (GPR39) is a zinc-sensing receptor (ZnR) that can sense changes in extracellular Zn2+, mediate Zn2+ signal transmission, and participate in the regulation of numerous physiological activities in living organisms. For example, GPR39 activates the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) and phosphatidylinositol3-kinase/protein kinase B (PI3K/AKT) signaling pathways upon Zn2+ stimulation, enhances the proliferation and differentiation of colonic cells, and regulates ion transport, as well as exerting other functions. In recent years, with the increased attention to animal gut health issues and the intensive research on GPR39, GPR39 has become a potential target for regulating animal intestinal health. On the one hand, GPR39 is involved in regulating ion transport in the animal intestine, mediating the Cl− efflux by activating the K+/Cl− synergistic protein transporter, and relieving diarrhea symptoms. On the other hand, GPR39 can maintain the homeostasis of the animal intestine, promoting pH restoration in colonic cells, regulating gastric acid secretion, and facilitating nutrient absorption. In addition, GPR39 can affect the expression of tight junction proteins in intestinal epithelial cells, improving the barrier function of the animal intestinal mucosa, and maintaining the integrity of the intestine. This review summarizes the structure and signaling transduction processes involving GPR39 and the effect of GPR39 on the regulation of intestinal health in animals, with the aim of further highlighting the role of GPR39 in regulating animal intestinal health and providing new directions and ideas for studying the prevention and treatment of animal intestinal diseases.

Alterations of Serum Magnesium Concentration in Animal Models of Seizures and Epilepsy—The Effects of Treatment with a GPR39 Agonist and Knockout of the Gpr39 Gene

Several ligands have been proposed for the GPR39 receptor, including the element zinc. The relationship between GPR39 and magnesium homeostasis has not yet been examined, nor has such a relationship in the context of seizures/epilepsy. We used samples from mice that were treated with an agonist of the GPR39 receptor (TC-G 1008) and underwent acute seizures (maximal electroshock (MES)- or 6-hertz-induced seizures) or a chronic, pentylenetetrazole (PTZ)-induced kindling model of epilepsy. MES seizures and PTZ kindling, unlike 6 Hz seizures, increased serum magnesium concentration. In turn, Gpr39-KO mice that underwent PTZ kindling displayed decreased concentrations of this element in serum, compared to WT mice subjected to this procedure. However, the levels of expression of TRPM7 and SlC41A1 proteins—which are responsible for magnesium transport into and out of cells, respectively—did not differ in the hippocampus between Gpr39-KO and WT mice. Furthermore, laser ablation inductively coupled plasma mass spectrometry applied to hippocampal slices did not reveal differences in magnesium levels between the groups. These data show the relationship between magnesium homeostasis and certain types of acute or chronic seizures (MES seizures or PTZ kindling, respectively), but do not explicitly support the role of GPR39 in mediating magnesium balance in the hippocampus in the latter model. However, decreased expression of TRPM7 and increased expression of SLC41A1—which were observed in the hippocampi of Gpr39-KO mice treated with TC-G 1008, in comparison to WT mice that received the same treatment—implicitly support the link between GPR39 and hippocampal magnesium homeostasis.

Diverse and Complementary Effects of Ghrelin and Obestatin

Ghrelin and obestatin are two "sibling proteins" encoded by the same preproghrelin gene but possess an array of diverse and complex functions. While there are ample literature documenting ghrelin's functions, the roles of obestatin are less clear and controversial. Ghrelin and obestatin have been perceived to be antagonistic initially; however, recent studies challenge this dogma. While they have opposing effects in some systems, they function synergistically in other systems, with many functions remaining debatable. In this review, we discuss their functional relationship under three "C" categories, namely complex, complementary, and contradictory. Their functions in food intake, weight regulation, hydration, gastrointestinal motility, inflammation, and insulin secretion are complex. Their functions in pancreatic beta cells, cardiovascular, muscle, neuroprotection, cancer, and digestive system are complementary. Their functions in white adipose tissue, thermogenesis, and sleep regulation are contradictory. Overall, this review accumulates the multifaceted functions of ghrelin and obestatin under both physiological and pathological conditions, with the intent of contributing to a better understanding of these two important gut hormones.

Zinc Ameliorates the Osteogenic Effects of High Glucose in Vascular Smooth Muscle Cells

In diabetic patients, medial vascular calcification is common and associated with increased cardiovascular mortality. Excessive glucose concentrations can activate the nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-kB) and trigger pro-calcific effects in vascular smooth muscle cells (VSMCs), which may actively augment vascular calcification. Zinc is able to mitigate phosphate-induced VSMC calcification. Reduced serum zinc levels have been reported in diabetes mellitus. Therefore, in this study the effects of zinc supplementation were investigated in primary human aortic VSMCs exposed to excessive glucose concentrations. Zinc treatment was found to abrogate the stimulating effects of high glucose on VSMC calcification. Furthermore, zinc was found to blunt the increased expression of osteogenic and chondrogenic markers in high glucose-treated VSMCs. High glucose exposure was shown to activate NF-kB in VSMCs, an effect that was blunted by additional zinc treatment. Zinc was further found to increase the expression of TNFα-induced protein 3 (TNFAIP3) in high glucose-treated VSMCs. The silencing of TNFAIP3 was shown to abolish the protective effects of zinc on high glucose-induced NF-kB-dependent transcriptional activation, osteogenic marker expression, and the calcification of VSMCs. Silencing of the zinc-sensing receptor G protein-coupled receptor 39 (GPR39) was shown to abolish zinc-induced TNFAIP3 expression and the effects of zinc on high glucose-induced osteogenic marker expression. These observations indicate that zinc may be a protective factor during vascular calcification in hyperglycemic conditions.

Role of GPR39 in Neurovascular Homeostasis and Disease

GPR39, a member of the ghrelin family of G protein-coupled receptors, is zinc-responsive and contributes to the regulation of diverse neurovascular and neurologic functions. Accumulating evidence suggests a role as a homeostatic regulator of neuronal excitability, vascular tone, and the immune response. We review GPR39 structure, function, and signaling, including constitutive activity and biased signaling, and summarize its expression pattern in the central nervous system. We further discuss its recognized role in neurovascular, neurological, and neuropsychiatric disorders.

Improved osteogenesis in rat femur segmental defects treated with human allograft and zinc adjuvants

Bone allograft is widely used to treat large bone defects or complex fractures. However, processing methods can significantly compromise allograft osteogenic activity. Adjuvants that can restore the osteogenic activity of processed allograft should improve clinical outcomes. In this study, zinc was tested as an adjuvant to increase the osteogenic activity of human allograft in a Rag2 null rat femoral defect model. Femoral defects were treated with human demineralized bone matrix (DBM) mixed with carboxy methyl cellulose containing ZnCl₂ (0, 75, 150, 300 µg) or Zn stearate (347 µg). Rat femur defects treated with DBM-ZnCl₂ (75 µg) and DBM-Zn stearate (347 µg) showed increased calcified tissue in the defect site compared to DBM alone. Radiograph scoring and µCT (microcomputed tomography) analysis showed an increased amount of bone formation at the defects treated with DBM-Zn stearate. Use of zinc as an adjuvant was also tested using human cancellous bone chips. The bone chips were soaked in ZnCl₂ solutions before being added to defect sites. Zn adsorbed onto the chips in a time- and concentration-dependent manner. Rat femur defects treated with Zn-bound bone chips had more new bone in the defects based on µCT and histomorphometric analyses. The results indicate that zinc supplementation of human bone allograft improves allograft osteogenic activity in the rat femur defect model.

The Zinc-Sensing Receptor GPR39 in Physiology and as a Pharmacological Target

The G-protein coupled receptor GPR39 is abundantly expressed in various tissues and can be activated by changes in extracellular Zn²⁺ in physiological concentrations. Previously, genetically modified rodent models have been able to shed some light on the physiological functions of GPR39, and more recently the utilization of novel synthetic agonists has led to the unraveling of several new functions in the variety of tissues GPR39 is expressed. Indeed, GPR39 seems to be involved in many important metabolic and endocrine functions, but also to play a part in inflammation, cardiovascular diseases, saliva secretion, bone formation, male fertility, addictive and depression disorders and cancer. These new discoveries offer opportunities for the development of novel therapeutic approaches against many diseases where efficient therapeutics are still lacking. This review focuses on Zn²⁺ as an endogenous ligand as well as on the novel synthetic agonists of GPR39, placing special emphasis on the recently discovered physiological functions and discusses their pharmacological potential.

Interaction between zinc, the GPR39 zinc receptor and the serotonergic system in depression

Zinc signalling has a crucial impact on the proper functioning of the brain. Disturbances within the zincergic system may lead to neuropsychological disorders, including major depression. Studying this disease and designing effective treatment is hampered by its heterogeneous etiology and the diversified nature of the symptoms. Over the years, studies have shown that zinc deficiency and disturbances in the expression profile of the zinc receptor - GPR39 - might be a useful neurobiological indicator of a pathological state. Zinc levels and the zinc receptor are altered by classic antidepressant treatment, which indicates possible reciprocity between the monoaminergic system and zinc signalling. Disruptions in this specific interplay might be a cause of a pathological depressive state, and restoring balance and cooperation between those systems might be key to a successful form of pharmacotherapy. In this review, we aim to describe interactions between the serotonergic and zincergic systems and to highlight their significance in the pathophysiology and treatment of depression.

Zinc as a Therapeutic Agent in Bone Regeneration

Zinc is an essential mineral that is required for normal skeletal growth and bone homeostasis. Furthermore, zinc appears to be able to promote bone regeneration. However, the cellular and molecular pathways through which zinc promotes bone growth, homeostasis, and regeneration are poorly understood. Zinc can positively affect chondrocyte and osteoblast functions, while inhibiting osteoclast activity, consistent with a beneficial role for zinc in bone homeostasis and regeneration. Based on the effects of zinc on skeletal cell populations and the role of zinc in skeletal growth, therapeutic approaches using zinc to improve bone regeneration are being developed. This review focuses on the role of zinc in bone growth, homeostasis, and regeneration while providing an overview of the existing studies that use zinc as a bone regeneration therapeutic.

Bioactive Three-Dimensional Graphene Oxide Foam/Polydimethylsiloxane/Zinc Silicate Scaffolds with Enhanced Osteoinductivity for Bone Regeneration

Nanocomposite scaffold materials have shown great prospect in promoting bone integration and bone regeneration. A three-dimensional graphene oxide foam/polydimethylsiloxane/zinc silicate (GF/PDMS/ZS) scaffold for bone tissue engineering was synthesized via dip coating and hydrothermal synthesis processes, resulting in the interconnected macroporous structure. The scaffold was characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric (TG) analysis. The result showed that scaffolds exhibiting a porous characteristic had organic-inorganic components similar to natural bone tissue. Moreover, the scaffolds possessed suitable pore size, high porosity, and good mechanical properties. In vitro experiments with mouse bone marrow mesenchymal stem cells (mBMSCs) revealed that the composite scaffold not only has great biocompatibility but also has the ability to induce mBMSC proliferation and preferential osteogentic differentiation. Thereafter, the expression of critical genes, ALP, RUNX2, VEGFA, and OPN, was activated. In vivo analysis of critical bone defect in rabbits demonstrated superior bone formation in defect sites in the GF/PDMS/ZS scaffold group at 12 weeks of post implantation without no significant inflammatory response. All the results validated that the GF/PDMS/ZS scaffold is a promising alternative for applications in bone regeneration.

GPR39 agonist TC-G 1008 promotes osteoblast differentiation and mineralization in MC3T3-E1 cells

Osteoporosis-related bone fracture and falls have a severe impact on patients' daily lives. Osteoblasts are bone-building cells that play a vital role in bone formation and remodeling. Imbalanced osteoblast differentiation could lead to osteoporosis. GPR39 is an orphan G protein-coupled receptor that mediates metabolic pathways. In this study, we show that GPR39 is expressed in MC3T3-E1 cells. Osteoblast differentiation culture media induces GPR39, suggesting that GPR39 is a differentiation-responsive factor. Activation of GPR39 using its selective agonist TC-G 1008 induces alkaline phosphatase (ALP), osteocalcin (OCN), and type I collagen (Col-I) expression, and increases cellular ALP activity and calcium deposition, implying that GPR activation promotes cells toward osteoblast differentiation. Treatment with TC-G 1008 also increases Runx-2 expression and AMPK activation. However, the inhibition of AMPK by Compound C abolished TC-G 1008-mediated ALP, OCN, and Col-I induction, and reduces ALP activity and cellular calcium deposition as well as Runx-2 induction. These data indicate that TC-G 1008-mediated GPR39 activation involves AMPK-mediated Runx-2 induction. In summary, our study uncovers a new role of GPR39 activation in osteoblast differentiation, implying that GPR39 could be a promising therapeutic target for osteoporosis.

Zinc supplements and bone health: The role of the RANKL-RANK axis as a therapeutic target

BACKGROUND

To this day, empirical data suggests that zinc has important roles in matrix synthesis, bone turnover, and mineralization and its beneficial effects on bone could be mediated through different mechanisms. The influence of zinc on bone turnover could be facilitated via regulating RANKL/RANK/OPG pathway in bone tissue. Therefore, the aim of the study was to conduct a review to investigate the possible effect of the zinc mediated bone remodeling via RANKL/RANK/OPG pathway.

METHODS

A comprehensive systematic search was performed in MEDLINE/PubMed, Cochrane Library, SCOPUS, and Google Scholar to explore the studies investigating the effect of zinc as a bone remodeling factor via RANKL/RANK/OPG pathway regulation. Subsequently, the details of the pathway and the impact of zinc supplements on RANKL/RANK/OPG pathway regulation were discussed.

RESULTS

The pathway could play an important role in bone remodeling and any imbalance between RANKL/RANK/OPG components could lead to extreme bone resorption. Although the outcomes of some studies are equivocal, it is evident that zinc possesses protective properties against bone loss by regulating the RANKL/RANK/OPG pathway. There are several experiments where zinc supplementation resulted in upregulation of OPG expression or decreases RANKL level. However, the results of some studies oppose this.

CONCLUSION

It is likely that sufficient zinc intake will elicit positive effects on bone health by RANKL/RANK/OPG regulation. Although the outcomes of a few studies are equivocal, it seems that zinc can exert the protective properties against bone loss by suppressing osteoclastogenesis via downregulation of RANKL/RANK. Additionally, there are several experiments where zinc supplementation resulted in upregulation of OPG expression. However, the results of limited studies oppose this. Therefore, aside from the positive role zinc possesses in preserving bone mass, further effects of zinc in RANKL/RANK/OPG system requires further animal/human studies.

Agonism of GPR39 displays protective effects against advanced glycation end-product (AGE)-induced degradation of extracellular matrix in human SW1353 cells

Excessive degradation of the cartilage articular extracellular matrix (ECM) in chondrocytes has been considered as an important pathological characteristics of OA. In the present study, we demonstrate that the G protein-coupled receptor GPR39 is expressed on SW1353 chondrocytes and is significantly downregulated in response to advanced glycation end products (AGEs). Our findings show that agonism of GPR39 exerts significant protective effects against AGE-induced degradation of articular extracellular matrix. Agonism of GPR39 rescued degradation of type II collagen by decreasing expression of the collagen-degrading enzymes matrix metalloproteinase (MMP)-3 and MMP-13. Additionally, agonism of GPR39 rescued AGE-induced suppression of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2. Agonism of GPR39 prevented degradation of aggrecan by downregulating AGE-induced expression of a disintegrin and metalloproteinase with type I thrombospondin motif (ADAMTS)-4 and ADAMTS-5. Finally, we demonstrate that the effects of GPR39 are mediated through the p38 mitogen activated protein kinase (MAPK)/nuclear factor-κB (NF-κB) cellular signaling pathway. Taken together, our findings show for the first time that targeted therapies involving GPR39 may provide a novel approach for the prevention and treatment of osteoarthritis.

The protective effects of the GPR39 agonist TC-G 1008 against TNF-α-induced inflammation in human fibroblast-like synoviocytes (FLSs)

Rheumatoid arthritis (RA) is a common immune-mediated chronic inflammatory joint disease of unknown etiology. While tumor necrosis factor-α(TNF-α) blockers have proven to be a beneficial treatment option for many patients, not all respond to such treatments. In the present study, we investigate the role of the recently discovered zinc-sensing G protein-couple receptor GPR39. To our knowledge, this study is the first to investigate the role of GPR39 in the context of RA using human fibroblast-like synoviocytes (FLS). We found that agonism of GPR39 using its specific agonist TC-G 1008 significantly ameliorated important markers of RA, including oxidative stress, mitochondrial dysfunction, expression of proinflammatory cytokines including interleukin-1β (IL-1β), IL-6, and monocyte chemoattractant protein 1 (MCP-1), and secretion of key matrix metalloproteinases (MMPs) including MMP-1, MMP-3 and MMP-13. Furthermore, we demonstrate that these may be mediated via the Janus-kinase (JNK), activating protein 1 (AP-1), and nuclear factor-κB (NF-κB) cellular signaling pathways. Our findings demonstrate for the first time the potential of GPR39 to mediate synovial inflammation, pannus invasion, and enzymatic degradation of articular extracellular matrix.

The role of GPCRs in bone diseases and dysfunctions

The superfamily of G protein-coupled receptors (GPCRs) contains immense structural and functional diversity and mediates a myriad of biological processes upon activation by various extracellular signals. Critical roles of GPCRs have been established in bone development, remodeling, and disease. Multiple human GPCR mutations impair bone development or metabolism, resulting in osteopathologies. Here we summarize the disease phenotypes and dysfunctions caused by GPCR gene mutations in humans as well as by deletion in animals. To date, 92 receptors (5 glutamate family, 67 rhodopsin family, 5 adhesion, 4 frizzled/taste2 family, 5 secretin family, and 6 other 7TM receptors) have been associated with bone diseases and dysfunctions (36 in humans and 72 in animals). By analyzing data from these 92 GPCRs, we found that mutation or deletion of different individual GPCRs could induce similar bone diseases or dysfunctions, and the same individual GPCR mutation or deletion could induce different bone diseases or dysfunctions in different populations or animal models. Data from human diseases or dysfunctions identified 19 genes whose mutation was associated with human BMD: 9 genes each for human height and osteoporosis; 4 genes each for human osteoarthritis (OA) and fracture risk; and 2 genes each for adolescent idiopathic scoliosis (AIS), periodontitis, osteosarcoma growth, and tooth development. Reports from gene knockout animals found 40 GPCRs whose deficiency reduced bone mass, while deficiency of 22 GPCRs increased bone mass and BMD; deficiency of 8 GPCRs reduced body length, while 5 mice had reduced femur size upon GPCR deletion. Furthermore, deficiency in 6 GPCRs induced osteoporosis; 4 induced osteoarthritis; 3 delayed fracture healing; 3 reduced arthritis severity; and reduced bone strength, increased bone strength, and increased cortical thickness were each observed in 2 GPCR-deficiency models. The ever-expanding number of GPCR mutation-associated diseases warrants accelerated molecular analysis, population studies, and investigation of phenotype correlation with SNPs to elucidate GPCR function in human diseases.

How cellular Zn2+ signaling drives physiological functions

Zinc is an essential micronutrient affecting many aspects of human health. Cellular Zn²⁺ homeostasis is critical for cell function and survival. Zn²⁺, acting as a first or second messenger, triggers signaling pathways that mediate the physiological roles of Zn²⁺. Transient changes in Zn²⁺ concentrations within the cell or in the extracellular region occur following its release from Zn²⁺ binding metallothioneins, its transport across membranes by the ZnT or ZIP transporters, or release of vesicular Zn²⁺. These transients activate a distinct Zn²⁺ sensing receptor, ZnR/GPR39, or modulate numerous proteins and signaling pathways. Importantly, Zn²⁺ signaling regulates cellular physiological functions such as: proliferation, differentiation, ion transport and secretion. Indeed, novel therapeutic approaches aimed to maintain Zn²⁺ homeostasis and signaling are evolving. This review focuses on recent findings describing roles of Zn²⁺ and its transporters in regulating physiological or pathological processes.

The Zinc Sensing Receptor, ZnR/GPR39, in Health and Disease

A distinct G-protein coupled receptor that senses changes in extracellular Zn²⁺, ZnR/GPR39, was found in cells from tissues in which Zn²⁺ plays a physiological role. Most prominently, ZnR/GPR39 activity was described in prostate cancer, skin keratinocytes, and colon epithelial cells, where zinc is essential for cell growth, wound closure, and barrier formation. ZnR/GPR39 activity was also described in neurons that are postsynaptic to vesicular Zn²⁺ release. Activation of ZnR/GPR39 triggers Gαq-dependent signaling and subsequent cellular pathways associated with cell growth and survival. Furthermore, ZnR/GPR39 was shown to regulate the activity of ion transport mechanisms that are essential for the physiological function of epithelial and neuronal cells. Thus, ZnR/GPR39 provides a unique target for therapeutically modifying the actions of zinc in a specific and selective manner.