Nathaniel A. Sowa

Ecto-5′-nucleotidase (CD73) inhibits nociception by hydrolyzing AMP to adenosine in nociceptive circuits

Ecto-5′-nucleotidase (NT5E, CD73) is a membrane-anchored protein that hydrolyzes extracellular adenosine 5′-monophosphate (AMP) to adenosine in diverse tissues but has not been directly studied in nociceptive neurons. We found that NT5E was located on peptidergic and nonpeptidergic nociceptive neurons in dorsal root ganglia (DRG) and on axon terminals in lamina II (the substantia gelatinosa) of spinal cord. NT5E was also located on epidermal keratinocytes, cells of the dermis, and on nociceptive axon terminals in the epidermis. Following nerve injury, NT5E protein and AMP histochemical staining were coordinately reduced in lamina II. In addition, AMP hydrolytic activity was reduced in DRG neurons and spinal cord of Nt5e−/− mice. The antinociceptive effects of AMP, when combined with the adenosine kinase inhibitor 5-iodotubericidin, were reduced by ∼50% in Nt5e−/− mice and were eliminated in Adenosine A1 receptor (A1R, Adora1) knock-out mice. Additionally, Nt5e−/− mice displayed enhanced sensitivity in the tail immersion assay, in the complete Freunds adjuvant model of inflammatory pain and in the spared nerve injury model of neuropathic pain. Collectively, our data indicate that the ectonucleotidase NT5E regulates nociception by hydrolyzing AMP to adenosine in nociceptive circuits and represents a new molecular target for the treatment of chronic pain. Moreover, our data suggest NT5E is well localized to regulate nucleotide signaling between skin cells and sensory axons.

Prostatic Acid Phosphatase Reduces Thermal Sensitivity and Chronic Pain Sensitization by Depleting Phosphatidylinositol 4,5-Bisphosphate

Prostatic acid phosphatase (PAP) is expressed in nociceptive dorsal root ganglion (DRG) neurons, functions as an ectonucleotidase, and generates adenosine extracellularly. Here, we found that PAP inhibits noxious thermal sensitivity and sensitization that is associated with chronic pain through sustained activation of the adenosine A1 receptor (A1R) and phospholipase C-mediated depletion of phosphatidylinositol 4,5-bisphosphate (PIP2). In mice, intrathecal injection of PAP reduced PIP2 levels in DRGs, inhibited thermosensation through TRPV1, and enduringly reduced thermal hyperalgesia and mechanical allodynia caused by inflammation, nerve injury, and pronociceptive receptor activation. This included inhibitory effects on lysophosphatidic acid, purinergic (ATP), bradykinin, and protease-activated (thrombin) receptors. Conversely, PIP2 levels were significantly elevated in DRGs from Pap−/− mice, and this correlated with enhanced thermal hyperalgesia and mechanical allodynia in Pap−/− mice. To directly test the importance of PIP2 in nociception, we intrathecally injected PIP2 into mice. This transiently (2 h) elevated PIP2 levels in lumbar DRGs and transiently (2 h) enhanced thermosensation. Additionally, thermal hyperalgesia and mechanical allodynia were enduringly enhanced when PIP2 levels were elevated coincident with injury/pronociceptive receptor stimulation. Nociceptive sensitization was not affected if PIP2 levels were elevated in the absence of ongoing pronociceptive receptor stimulation. Together, our data suggest that PIP2 levels in DRGs directly influence thermosensation and the magnitude of nociceptive sensitization. Moreover, our data suggest there is an underlying “phosphoinositide tone” that can be manipulated by an adenosine-generating ectonucleotidase. This tone regulates how effectively acute nociceptive insults promote the transition to chronic pain.

Recombinant Mouse PAP Has pH-Dependent Ectonucleotidase Activity and Acts through A1-Adenosine Receptors to Mediate Antinociception

Prostatic acid phosphatase (PAP) is expressed in nociceptive neurons and functions as an ectonucleotidase. When injected intraspinally, the secretory isoforms of human and bovine PAP protein have potent and long-lasting antinociceptive effects that are dependent on A1-adenosine receptor (A1R) activation. In this study, we purified the secretory isoform of mouse (m)PAP using the baculovirus expression system to determine if recombinant mPAP also had antinociceptive properties. We found that mPAP dephosphorylated AMP, and to a much lesser extent, ADP at neutral pH (pH 7.0). In contrast, mPAP dephosphorylated all purine nucleotides (AMP, ADP, ATP) at an acidic pH (pH 5.6). The transmembrane isoform of mPAP had similar pH-dependent ectonucleotidase activity. A single intraspinal injection of mPAP protein had long-lasting (three day) antinociceptive properties, including antihyperalgesic and antiallodynic effects in the Complete Freunds Adjuvant (CFA) inflammatory pain model. These antinociceptive effects were transiently blocked by the A1R antagonist 8-cyclopentyl-1, 3-dipropylxanthine (CPX), suggesting mPAP dephosphorylates nucleotides to adenosine to mediate antinociception just like human and bovine PAP. Our studies indicate that PAP has species-conserved antinociceptive effects and has pH-dependent ectonucleotidase activity. The ability to metabolize nucleotides in a pH-dependent manner could be relevant to conditions like inflammation where tissue acidosis and nucleotide release occur. Lastly, our studies demonstrate that recombinant PAP protein can be used to treat chronic pain in animal models.

Regulator of G-protein signaling 14 (RGS14) is a selective H-Ras effector.

Background Regulator of G-protein signaling (RGS) proteins have been well-described as accelerators of Gα-mediated GTP hydrolysis (“GTPase-accelerating proteins” or GAPs). However, RGS proteins with complex domain architectures are now known to regulate much more than Gα GTPase activity. RGS14 contains tandem Ras-binding domains that have been reported to bind to Rap- but not Ras GTPases in vitro, leading to the suggestion that RGS14 is a Rap-specific effector. However, more recent data from mammals and Drosophila imply that, in vivo, RGS14 may instead be an effector of Ras. Methodology/Principal Findings Full-length and truncated forms of purified RGS14 protein were found to bind indiscriminately in vitro to both Rap- and Ras-family GTPases, consistent with prior literature reports. In stark contrast, however, we found that in a cellular context RGS14 selectively binds to activated H-Ras and not to Rap isoforms. Co-transfection / co-immunoprecipitation experiments demonstrated the ability of full-length RGS14 to assemble a multiprotein complex with components of the ERK MAPK pathway in a manner dependent on activated H-Ras. Small interfering RNA-mediated knockdown of RGS14 inhibited both nerve growth factor- and basic fibrobast growth factor-mediated neuronal differentiation of PC12 cells, a process which is known to be dependent on Ras-ERK signaling. Conclusions/Significance In cells, RGS14 facilitates the formation of a selective Ras·GTP-Raf-MEK-ERK multiprotein complex to promote sustained ERK activation and regulate H-Ras-dependent neuritogenesis. This cellular function for RGS14 is similar but distinct from that recently described for its closely-related paralogue, RGS12, which shares the tandem Ras-binding domain architecture with RGS14.

Perinatal Depression in HIV-Infected African Women: A Systematic Review

OBJECTIVE To systematically review the literature on prevalence and incidence of perinatal depression in human immunodeficiency virus (HIV)-infected African women. DATA SOURCES We searched 17 databases, including PubMed, PsycINFO, Cochrane, EMBASE, Web of Science, ClinicalTrials.gov, Google Scholar, and OpenGrey, from inception through August 2014 using the search strategy ((antenatal OR peripartum OR perinatal OR postnatal OR postpartum) AND (depression OR mental disorder) AND HIV AND Africa NOT (-) American). STUDY SELECTION We included English-language articles on studies conducted in Africa with prevalence or incidence rates of diagnostically confirmed depression or suspected depression in HIV-infected women during pregnancy through 12 months postpartum. DATA EXTRACTION We examined details of study design, location, means of measurement, incidence and prevalence rates of diagnostically confirmed depression or suspected depression and any associated risk factors for development of depression. Mean prevalence rates were calculated and weighted based on study size. RESULTS Twenty-two articles met inclusion criteria. Two reported diagnostically confirmed antenatal depression, and 9 reported suspected antenatal depression prevalence. Two reported diagnostically confirmed postnatal depression, and 10 reported suspected postnatal depression prevalence. Weighted mean prevalence of antenatal depression was 23.4%, and suspected antenatal depression was 43.5%. Weighted mean prevalence of postnatal depression was 22.5%, and suspected postnatal depression was 31.1%. No studies reported incidence rates. CONCLUSIONS Few studies have examined the rate of perinatal depression in HIV-infected African women. Existing studies show a high prevalence of perinatal depression, with even higher prevalence rates of suspected depression. No data on the incidence of perinatal depression in this population exist.

Predictors of depression recovery in HIV-infected individuals managed through measurement-based care in infectious disease clinics.

BACKGROUND Treatment of comorbid chronic disease, such as depression, in people living with HIV/AIDS (PLWHA) increasingly falls to HIV treatment providers. Guidance in who will best respond to depression treatment and which patient-centered symptoms are best to target is limited. METHODS Bivariable analyses were used to calculate hazard ratios for associations between baseline demographic, mental health-related, and HIV-related factors on time to first depression remission among PLWHA enrolled in a randomized trial of measurement-based antidepressant management. Time-updated factors also were analyzed at time of antidepressant (AD) initiation/adjustment and 8 weeks post AD initiation/adjustment. RESULTS Baseline comorbid depression and anxiety; comorbid depression, anxiety and substance abuse; and generalized anxiety disorder predicted a slower time to first remission. Being on ART but non-adherent, having panic disorder, having a history of a major depressive episode, or having been in HIV care for >10 years prior to study initiation predicted a faster time to first remission. Sleep difficulty or fatigue at the time of AD initiation/adjustment predicted a slower time to remission. In non-remitters at 8 weeks post AD initiation/adjustment, sleep difficulty, anxiety, and fatigue each predicted a slower time to remission. LIMITATIONS Remission was determined by PHQ-9 scores, not diagnostic criteria. The results may apply only to depression recovery in this particular model of treatment. We conducted only exploratory analyses to determine magnitude of effects. CONCLUSIONS Baseline comorbid anxiety with or without substance abuse predicts slower time to depression remission among PLWHA treated in HIV clinics. Targeting anxiety or fatigue at the time of AD initiation/adjustment or sleep difficulty, anxiety, and fatigue at 8 weeks post AD initiation/adjustment could shorten time to depression remission in this model.

Complexities of Diagnosing Neuroleptic Malignant Syndrome in a Patient with Burn Injury: Could Stimulant Abuse be a Risk Factor?

Received February 7, 2016; revisedMay 6, 2016; acceptedMay 6, 2016. FromUniversity of North Carolina School ofMedicine, Chapel Hill, NC (SLL, GJG); University of North Carolina Hospitals, Chapel Hill, NC (NAS). Send correspondence and reprint requests to Sarah L. Laughon, M.D., University of North Carolina School of Medicine, Neurosciences Hospital 2nd Floor, CB #7160, Chapel Hill, NC 27599-7160; e-mail: sarah_laughon@med.unc.edu & 2016TheAcademy of PsychosomaticMedicine. Published by Elsevier Inc. All rights reserved. Introduction