Substance use disorder (SUD) is a chronic condition with maintained abuse of a substance leading to physiological and psychological alterations and often changes in cognitive and social behaviours. Current therapies mainly consist of psychotherapy coupled with medication; however, alarmingly high relapse rates reveal the shortcomings of the current standard of care. The signalling and expression profile, and neurological function of the serotonin 2C receptor (5-HT2C receptor) make it an ideal candidate of interest for the treatment of SUD. This is further corroborated by pre-clinical and clinical evidence of therapeutically relevant compounds acting at the 5-HT2C receptor. Notwithstanding, drug binding at closely related serotonin receptor subtypes has impeded drug development. More recently, psychedelics, which broadly act at 5-HT2 receptors, have indicated promising potential for the treatment of SUD, implicating in part, the 5-HT2C receptor. The modern psychedelic movement has rekindled therapeutic interest in the 5-HT2C receptor, resulting in an influx of new studies, especially structural analyses. This review delves into the structural, molecular and cellular mechanisms governing the 5-HT2C receptor function, in the context of SUD. This provides the basis of the preclinical and clinical evidence for their role in SUD and highlights the potential for future exploration.
Background and Purpose: Psoriasis is an inflammatory skin disease of chronic recurrence mediated by the interaction between IL-17 and keratinocytes, which sustains a vicious circle of inflammation. Currently, there is no safe and effective natural medicine for the clinical treatment of psoriasis. Given its prominent anti-proliferative and anti-inflammatory properties, we investigated the mechanism of allicin improving psoriasis. Experimental Design: Pharmacodynamics and toxicology experimental studies were estimated after topical administration of allicin on the skin of mice. Changes in inflammatory factors expression were analyzed by qPCR and immunohistochemistry after topical treatment with allicin in mice with psoriasis-like lesions induced by imiquimod. The impacts of allicin on proliferation and apoptosis of keratinocytes were analyzed by CCK8 assay and flow cytometry. The interaction between IL-17A and keratinocytes was studied using HaCaT cells, and the mechanism of action of allicin was explored by Western Blot. Transcriptomic changes following the action of allicin were probed by RNA-seq. Key Results: Our study demonstrated that allicin significantly improved the epidermal structure by inhibiting excessive proliferation and evasion of apoptosis of keratinocytes. Furthermore, allicin reduced the secretion of inflammatory cytokines (IL-17A/F, IL-22, IL-12, IL-20), chemokines (CXCL2, CXCL5, CCL20), and antibacterial peptides (S100A8/9). Mechanistically, allicin directly inhibited the IL-17-induced TRAF6/MAPK/NF-κB and STAT3/NF-κB signaling cascades in keratinocytes, thus breaking the positive inflammation feedback and alleviating imiquimod-induced psoriasis-like dermatitis in mice. Importantly, topical administration of allicin did not cause skin allergy, and the safety and adaptability of long-term application were verified.
Background and Purpose: Recent biochemical and pharmacological studies have reported that in several tissues and cell types, microsomal prostaglandin E2 synthase (mPGES) and peroxisome proliferator-activated receptor-γ (PPAR-γ) expression are modulated by a variety of inflammatory factors and stimuli Considering that very little is known about the biological effects promoted by IL-17 in the context of mPGES-1/PPAR-γ modulation, we sought to investigate the contribution of this unique cytokine on these integrated pathways during the onset of inflammation. Experimental Approach: We evaluated PF 9184 (mPGES-1 antagonist) and Troglitazone (PPAR-γ agonist) activity utilising integrated in vitro and in vivo approaches. The dorsal air pouch model was employed, and inflammatory infiltrates were analysed by flow cytometry. Locally produced cyto-chemokines and prostaglandins were assessed using ELISA assays. Western blots were also employed to determine the activity of various enzymes involved in downstream signalling pathways. Key Results: PF 9184 and Troglitazone, in a time and dose-dependent manner, were shown to significantly modulate leukocyte infiltration, myeloperoxidase activity, and the expression of COX-2/mPGES-1, NF-кB/IкB-α and mPGDS-1/PPAR-γ induced by IL-17. Moreover, both compounds were found to modulate prostaglandins (PGE2, PGD2, and PGJ2) production, the expression of different pro-inflammatory cyto-chemokines and the recruitment of inflammatory monocytes in response to IL-17. Conclusions and Implications: Collectively, the data presented suggests that IL-17 may constitute a specific modulator of inflammatory monocytes during later phases of the inflammatory response. Therefore, the results of this study show, for the first time, that IL-17/mPGES-1/PPAR-γ “axis” could represent a potential therapeutic target for inflammatory-based and immune-mediated diseases.
Hydrogen sulfide (H2S) together with polysulfides (H2Sn, n>2) are signaling molecules like nitric oxide (NO) with various physiological roles including regulation of neuronal transmission, vascular tone, inflammation, oxygen sensing etc. H2S and H2Sn diffuse to the target proteins to S-sulfurate their cysteine residues to induce the conformational changes to alter the activity. On the other hand, 3-mercaptopyruvate sulfurtransferase transfers sulfur from a substrate 3-mercaptopyruvate to the cysteine residues of acceptor proteins. A similar mechanism has also been identified in S-nitrosylation. S-sulfuration and S-nitrosylation by enzymes proceed only inside the cell, while reactions induced by H2S, H2Sn and NO even extend to the surrounding cells. Disturbance of signaling by these molecules as well as S-sulfuration and S-nitrosylation causes many neuronal diseases. This review focuses on the signaling by H2S and H2Sn with S-sulfuration compared with those of NO and S-nitrosynation, and discuss on their roles in physiology and pathophysiology.
Background and purpose: Increasing evidence has shown that human cholestasis is closely related to hepatic macrophage accumulation and activation. Research has indicated that peroxisome proliferator-activated receptor-g (PPARg) activation exerts liver protection in cholestatic liver disease (CLD), particularly by ameliorating inflammation and fibrosis, thus limiting disease progression. However, existing PPARg agonists, such as troglitazone and rosiglitazone, have significant side effects that impede their clinical application in the treatment of CLD. In this study, we found that tectorigenin (TEC) can alleviate intrahepatic cholestasis in mice by activating PPARg. Experimental approach: Wild-type mice received intragastric administration of a-naphthylisothiocyanate (ANIT) or were fed a diet containing 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) to establish an experimental intrahepatic cholestasis model and TEC intervention simultaneously, followed by determination of intrahepatic cholestasis and the involved mechanisms. In addition, PPARg deficient mice were administered ANIT and/or TEC to determine whether TEC exerts its liver protection effect by activating PPARg. Key results: Our results demonstrated that TEC intervention alleviated intrahepatic cholestasis by inhibiting hepatic macrophage recruitment and activation as well as promoting the expression of bile transporters through activating PPARg. Furthermore, our results show that TEC increased bile salt export pump (Bsep) expression through enhanced PPARg binding to the Bsep promoter. We also demonstrated that PPARg deficiency blocked the hepatocyte protective effect of TEC during cholestasis. Conclusions and implications: In conclusion, TEC reduced hepatic macrophage recruitment and activation, and enhanced bile acid export by activating PPARg. Taken together, our results suggest that TEC is a potential drug for the prevention of CLD.
Background and Purpose Squalene epoxidase (SQLE) is a key enzyme involved in cholesterol biosynthesis, but increasing evidence reveals that SQLE is abnormally expressed in some types of malignant tumors, and the underlying mechanism remains poorly understood. Experimental Approach Bioinformatics analysis and RNA sequencing were applied to detect to differentially expressed genes in clinical HCC tumors. AnnexinV-FITC/PI, EdU assay, transwell, IHC staining, cytoskeleton F-actin filaments assay, RNA sequencing, dual-luciferase reporters and HE staining were evaluated to investigate the pharmacological effects and possible mechanisms of SQLE. Key Results We found that SQLE expression is specifically elevated in HCC tumors, correlating with poor clinical outcomes. SQLE promoted HCC growth, EMT, and metastasis both in vitro and in vivo. In contrast, silencing of SQLE expression prevented HCC development. Both RNA-seq and functional experiments revealed that the protumorigenic effect of SQLE on HCC is closely related to the activation of cellular TGF-β/SMAD signaling, but interestingly, the stimulatory effect of SQLE on TGF-β/SMAD signaling and HCC development is also critically dependent on STRAP, a serine and threonine kinase. SQLE expression is well correlated with STRAP in HCC, and further, to amplify TGF-β/SMAD signaling, SQLE even transcriptionally increased STRAP gene expression mediated by the trans-acting factor AP-2α. Finally, as a chemical inhibitor of SQLE, NB-598 markedly inhibited HCC cell growth and tumor development in mouse models. Conclusions and Implications Taken together, SQLE serves as an oncogene in HCC development by activating TGF-β/SMAD signaling, and targeting SQLE could be useful in drug development and therapy for HCC.
Background and Purpose: Traumatic brain injury (TBI) remains a leading cause of mortality and morbidity in young adults. The role of iron in potentiating neurodegeneration following TBI has gained recent interest since iron deposition has been detected in the injured brain in the weeks to months post-TBI, in both the preclinical and clinical setting. A failure in iron homeostasis can lead to oxidative stress, inflammation and excitotoxicity; and whether this is a cause or consequence of the long-term effects of TBI remains unknown. Experimental approach: We investigated the role of iron, and the effect of therapeutic intervention using a brain-permeable iron chelator, deferiprone, in a controlled cortical impact mouse model of TBI. An extensive assessment of cognitive, motor and anxiety/depressive outcome measures were examined, and neuropathological and biochemical changes, over a 3-month period post-TBI. Key Results: Lesion volume was significantly reduced at 3 months, which was preceded by a reduction in astrogliosis and a preservation of neurons in the injured brain at 2 weeks and/or 1-month post-TBI in mice receiving oral deferiprone. Deferiprone treatment showed significant improvements in neurological severity scores and locomotor/gait performance, and cognitive function, and attenuated anxiety-like symptoms post-TBI. Deferiprone reduced iron levels, oxidative stress and altered expression of neurotrophins in the injured brain over this period. Conclusion and Implications: Our findings support a detrimental role of iron in the injured brain and suggest that deferiprone (or similar iron chelators) may be promising therapeutic approaches to improve survival, functional outcomes and quality of life following TBI.
In the search to rapidly identify effective therapies that will mitigate the morbidity and mortality of COVID-19, attention has been directed towards the repurposing of existing drugs. Candidates for repurposing include drugs that target COVID-19 pathobiology, including agents that alter angiotensin signaling. Recent data indicate that key findings in COVID-19 patients include thrombosis and endothelitis Activation of PAR1 (protease activated receptor 1), in particular by the protease thrombin, is a critical element in platelet aggregation and coagulation. PAR1 activation also impacts on the actions of other cell types involved in COVID-19 pathobiology, including endothelial cells, fibroblasts and pulmonary alveolar epithelial cells. Vorapaxar is an approved inhibitor of PAR1, used for treatment of patients with myocardial infarction or peripheral arterial disease. Here, we discuss evidence implying a possible beneficial role for vorapaxar in the treatment of COVID-19 patients and in addition, other as-yet non-approved antagonists of PAR1 and PAR4.
Peptide-based cancer therapy has been of great interest due to the unique advantages of peptides, such as the low molecular weight, the ability to specifically target tumor cells, easy availability and low toxicity in normal tissues. Therefore, identify and synthesize novel peptides could provide a promising choice to patients with cancer. The antitumor second generation peptide CIGB-552 has been developed as a candidate to cancer treatment. Proteomic and genomic studies have identified the intracellular protein COMMD1 as the specific target of CIGB-552. This peptide penetrates inside tumor cells to induce the proteasomal degradation of RelA, causing the termination of NF-kB signaling. The antitumor activity of CIGB-552 has been validated in vitro in different human cancer cell lines, as well as in vivo in syngeneic and xenograft tumor mouse models and in cancer-bearing dogs. The aim of this review is to present and discuss the experimental data about CIGB-552, its mechanism of action and its therapeutic potential in human chronic diseases. This peptide is already in phase I of clinical trials as antineoplastic drug, but also has possible application to other inflammatory and metabolic conditions.
Fibrosis is a common process of tissue repair response to multiple injuries in all chronic progressive diseases, which featured with excessive deposition of extracellular matrix. Actually fibrosis can occur in all organs and tends to be nonreversible with the progresses of the diseases. Different cells types in different organs are involved in the occurrence and development of fibrosis, i.e. hepatic stellate cell, pancreatic stellate cell, fibroblasts, myofibroblasts. Present studies have shown that several programmed cell deaths including apoptosis, autophagy, ferroptosis, and necroptosis were closely related to organ fibrosis. Among these programmed cell deathes type, necroptosis, an emerging regulated cell death type were regard as a huge potential target to ameliorate organ fibrosis. In this review, we summarized the role of necroptosis signaling in organ fibrosis, and collected the present small molecule compounds targeting necroptosis. In addition, we have discussed the potential challenges, opportunities and open questions in using necroptosis signaling as a potential target for antifibrotic therapies.
Background and Purpose: Improvement of cognitive deficits in schizophrenia remains an unmet need due to the lack of new therapies and drugs. Recent studies have reported that fingolimod, an immunomodulatory drug for treating multiple sclerosis, demonstrates anti-inflammatory and neuroprotective effects in several neurological disease models. This suggests its usefulness for ameliorating cognitive dysfunction in schizophrenia. Herein, we assessed the efficacy profile and mechanism of fingolimod in a rat model of phencyclidine (PCP)-induced schizophrenia. Experimental Approach: Sprague-Dawley rats were treated with PCP for 14 days. The therapeutic effect of fingolimod on cognitive function was assessed using the Morris water maze and fear conditioning tests. Hippocampal neurogenesis and the expression of astrocytes and microglia were evaluated by immunostaining. Cytokine expression was quantified using multiplexed flow cytometry. Brain-derived neurotrophic factor expression and phosphorylation of extracellular signal-regulated kinase were determined using western blot analysis. Key Results: Fingolimod attenuated cognitive deficits and restored hippocampal neurogenesis in a dose-dependent manner in PCP-treated rats. Fingolimod treatment exerted anti-inflammatory effects by inhibiting microglial activation and IL-6 and IL-1β pro-inflammatory cytokine expression. The underlying mechanism involves the upregulation of brain-derived neurotrophic factor protein expression and activation of the extracellular signal-regulated kinase signalling pathway. Conclusion and Implications: To the best of our knowledge, this is the first preclinical study to assess the effects of fingolimod on cognitive function in schizophrenia models. Our results support the role of the immune system in cognitive alterations in schizophrenia and highlight the potential of immunomodulatory strategies to improve cognitive deficits in schizophrenia.
Background and Purpose Coordinated endothelial control of cardiovascular function is proposed to occur by endothelial cell communication via gap junctions and connexins. To study intercellular communication, the pharmacological agents carbenoxolone (CBX) and 18β glycyrrhetinic acid (18βGA) are used widely as connexin inhibitors and gap junction blockers. Experimental Approach We investigated the effects of CBX and 18βGA on IP3-evoked intercellular Ca2+ waves in the endothelium of intact mesenteric resistance arteries. Key Results Acetylcholine (ACh)-evoked IP3-mediated Ca2+ release and propagated waves were inhibited by CBX (100µM) and 18βGA (40µM). Unexpectedly, the Ca2+ signals were inhibited uniformly in all cells, suggesting that CBX and 18βGA reduced Ca2+ release. Localised photolysis of caged IP3 (cIP3) was used to provide precise spatiotemporal control of site of cell activation. Local cIP3 photolysis generated reproducible Ca2+ increases and Ca2+ waves that propagated across cells distant to the photolysis site. CBX and 18βGA each blocked Ca2+ waves in a time dependent manner by inhibiting the initiating IP3-evoked Ca2+ release event rather than block of gap junctions. This effect was reversed on drug washout, and was unaffected by small or intermediate K+-channel blockers. Furthermore, CBX and 18βGA each rapidly and reversibly collapsed the mitochondrial membrane potential. Conclusion and Implications CBX and 18βGA inhibit IP3-mediated Ca2+ release and depolarise the mitochondrial membrane potential. These results suggest that CBX and 18βGA block cell-cell communication by acting at sites that are unrelated to gap junctions.
Background and Purpose: Heart failure can reflect impaired contractile function at the myofilament level. In healthy hearts, myofilaments become more sensitive to Ca2+ as cells are stretched. This represents a fundamental property of myocardium that contributes to the Frank-Starling response, although the molecular mechanisms underlying the effect remain unclear. Mavacamten is a drug that binds to myosin, which is under investigation as a potential therapy for cardiovascular disease. We tested how mavacamten affects the sarcomere-length dependence of Ca2+-sensitive isometric contraction to determine how mavacamten might modulate the Frank-Starling mechanism. Experimental Approach: Multicellular preparations from the left ventricular free wall of hearts procured from organ donors were chemically permeabilized and Ca2+-activated in the presence or absence of 0.5 μM mavacamten at 1.9 or 2.3 µm sarcomere length (37°C). Isometric force and frequency-dependent viscoelastic myocardial stiffness measurements were made. Key Results: At both sarcomere lengths, mavacamten reduced maximal force and Ca2+-sensitivity of contraction. In the presence and absence of mavacamten, Ca2+-sensitivity of force increased as sarcomere length increased. This suggests that the length-dependent activation response was maintained in human myocardium, even though mavacamten reduced Ca2+-sensitivity. There were subtle effects of mavacamten reducing force values under relaxed conditions (pCa 8.0), as well as slowing myosin cross-bridge recruitment and speeding cross-bridge detachment under maximally activated conditions (pCa 4.5). Conclusion and Implications: Mavacamten did not eliminate sarcomere length-dependent increases in the Ca2+-sensitivity of contraction in myocardial strips from organ donors at physiological temperature. Pharmaceuticals that modulate myofilament function may be useful therapies for cardiovascular disease.
Background and Purpose L-DOPA induced dyskinesia is a debilitating side effect of treating Parkinson’s disease with L-DOPA. There is a need to discover a treatment that has the same benefits as L-DOPA treatment without the associated side effects. Here, we demonstrate the anti-dyskinetic potential of doxycycline and the analog compound COL-3 (without antimicrobial activity) in hemiparkinsonian rats presenting L-DOPA-induced dyskinesia. Experimental Approach Wistar adult male rats received a unilateral medial forebrain bundle injection of 6-hydroxydopamine and were then orally administered L-DOPA once a day for 14 days. This resulted in dyskinetic-like behavior. Key Results A single injection of doxycycline (intraperitoneal) or COL-3 (intracerebroventricular) together with L-DOPA attenuated the dyskinesia. Co-treatment with doxycycline from the first day of L-DOPA suppressed the onset of dyskinesia. The improved motor responses to L-DOPA remained intact in the presence of doxycycline or COL-3, indicating the preservation of the L-DOPA benefits. Doxycycline treatment was associated with decreased expression of FosB, cyclooxygenase-2, astrocytes, and microglia, which had previously been found to be elevated in the basal ganglia of rats exhibiting dyskinesia. In addition, metalloproteinase-2/-9 activity, metalloproteinase-3 expression, and production of reactive oxygen species in the basal ganglia of dyskinetic rats showed a significant positive correlation with the intensity of dyskinesia, which was decreased with the doxycycline treatment. Conclusion and Implications Given the long-established and safe use of doxycycline and the similar effect of COL-3 (without antimicrobial activity), this study indicates that both drugs should undergo testing for their ability to reduce signs of dyskinesia induced by L-DOPA in patients with Parkinson’s disease.
Background: Post-ischemic inflammation contributes to worsening of ischemic brain injury and in this process, the inflammasomes play a key role. Inflammasomes are cytosolic multiprotein complexes which upon assembly activate the maturation and secretion of the inflammatory cytokines IL-1β and IL-18. However, participation of the NLRP3 inflammasome in ischemic stroke remains controversial. Our aims were to determine the role of NLRP3 in ischemia and to explore the mechanism involved in the potential protective effect of the neurovascular unit. Methods: WT and NLRP3 knock-out mice were subjected to ischemia by middle cerebral artery occlusion (60 minutes) with or without treatment with MCC950 at different time points post-stroke. Brain injury was measured histologically with 2,3,5-triphenyltetrazolium chloride (TTC) staining. Results: We identified a time-dependent dual effect of NLRP3. While neither the pre-treatment with MCC950 nor the genetic approach (NLRP3 KO) proved to be neuroprotective, post-reperfusion treatment with MCC950 significantly reduced the infarct volume in a dose-dependent manner. Importantly, MCC950 improved the neuro-motor function and reduced the expression of different pro-inflammatory cytokines (IL-1β, TNF-α), NLRP3 inflammasome components (NLRP3, pro-caspase-1), protease expression (MMP9) and endothelial adhesion molecules (ICAM, VCAM). We observed a marked protection of the blood-brain barrier (BBB), which was also reflected in the recovery of the tight junctions proteins (ZO-1, Claudin-5). Additionally, MCC950 produced a reduction of the CCL2 chemokine in blood serum and in brain tissue, which lead to a reduction in the immune cell infiltration. Conclusions: These findings suggest that post-reperfusion NLRP3 inhibition may be an effective acute therapy for protecting the blood-brain barrier in cerebral ischemia with potential clinical translation.
Background and Purpose: Cigarette smoking (CS) is the major risk factor for developing COPD and related skeletal muscle dysfunction. It has been postulated that CS exposure may directly causes muscle dysfunction via the induction of oxidative stress. The present study examined the effect of a potent Nox inhibitor and ROS scavenger, apocynin on CS-induced muscle dysfunction. Experimental Approach: Male BALB/c mice were exposed to either room air (sham) or CS generated from 9 cigarettes per day, 5 days a week for 8 weeks with or without apocynin treatment (5 mg·kg-1 w/v, intraperitoneal injection). C2C12 myotubes exposed to either hydrogen peroxide (H2O2) or water-soluble cigarette smoke extract (CSE) with or without apocynin (500 nM), was set up as an experimental model in vitro. Key Results: Eight weeks of CS exposure caused significant lung inflammation and muscle dysfunction in mice; evidenced by a 10% loss in muscle mass and 54% loss in contractile function of tibialis anterior, attributable to altered myogenic homeostasis and protein oxidation. These effects were prevented by apocynin administration. In C2C12 myotubes, direct exposure to H2O2 or CSE caused myofiber wasting, which was associated with altered myogenic homeostasis marked by ~50% loss in muscle-derived insulin-like growth factor (IGF)-1 and 1.5-fold increase in myostatin expression. Apocynin treatment completely attenuated CSE-induced Nox2 expression, preserving muscle-derived IGF-1 expression and downstream mammalian target of rapamycin (mTOR) signaling pathway, thereby preventing myofiber wasting. Conclusion and Implications: Targeted pharmacological inhibition of Nox-derived ROS may alleviate the lung and systemic manifestations in smokers with COPD.
Background: Vascular TRPV channels have emerged as important regulators of vascular tone. TRPV1 and endothelin-1 (ET-1) are independently associated with the pathophysiology of coronary vasospasm but the relationship between their vasomotor functions remains unclear. We characterized the vasomotor function of TRPV1 channels in human arterioles and investigated regulation of their vasomotor function by ET-1. Approach: Arterioles were threaded on two metal wires, equilibrated in a physiological buffer at 37 oC and exposed to increasing concentrations of capsaicin in the absence or presence of SB366791 (TRPV1-selective inhibitor) or GF109203X (PKC-selective inhibitor). Some arterioles were preconstricted with ET-1 or phenylephrine or high K+ buffer. TRPV1 mRNA and protein expression in human arteries were assessed. Results: TRPV1 transcripts and proteins were detected in human resistance arteries. Capsaicin (1 µM) induced concentration-dependent constriction of endothelium-intact (35 ± 8 %) and endothelium-denuded (43 ± 11 %) human adipose arterioles (HAA), which was significantly inhibited by SB366791 (0.2 ± 0.1 %). Preconstriction of HAA with ET-1, but not high potassium buffer or phenylephrine, significantly potentiated capsaicin-induced constriction (33 ± 7 % vs 12 ± 8 %). GF109203X significantly inhibited potentiation of capsaicin-induced constriction by ET-1. Conclusion: TRPV1 channels are expressed in the human vasculature and can influence vascular tone of human arterioles upon activation. Their vasomotor function is modulated by ET-1, mediated in part by PKC.. These findings reveal a novel interplay between ET-1 signaling and TRPV1 channels in human VSMC, adding to our understanding of the ion channel mechanisms that regulate human arteriolar tone and may also contribute to the pathophysiology of coronary vasospasm.
Infertility rates for both females and males have increased continuously in recent years. Currently, effective treatments for male infertility with defined mechanisms or targets are still lacking. G protein-coupled receptors (GPCRs) are the largest class of drug targets, but their functions and the implications on therapeutic development for male infertility largely remain elusive. Nevertheless, recent studies have shown that several members of the GPCR superfamily play crucial roles in the maintenance of ion-water homeostasis of the epididymis, development of the efferent ductules, formation of the blood-epididymal barrier, and maturation of sperm. Knowledge of the functions, genetic variations, and working mechanisms of such GPCRs, along with the drugs and ligands relevant to their specific functions, provide future directions and elicit great arsenal for potential therapy development for treating male infertility.