Glial-restricted precursors: Patterns of expression of opioid receptors and relationship to human immunodeficiency virus-1 Tat and morphine susceptibility in vitro

Abstract

Recent evidence suggests that HIV-induced pathogenesis is exacerbated by opioid abuse and that the synergistic toxicity may result from direct actions of opioids in immature glia or glial precursors. To assess whether opioids and HIV proteins are directly toxic to glial-restricted precursors (GRPs), we isolated neural stem cells from the incipient spinal cord of embryonic day 10.5 ICR mice. GRPs were characterized immunocytochemically and by RTPCR. At 1 day in vitro (DIV), GRPs failed to express μ (MOR or MOP) or κ-opioid receptors (KOR or KOP); however, at 5 DIV, most GRPs expressed MOR and KOR. The effects of morphine (500 nM) and/or Tat (100 nM) on GRP viability were assessed in GRPs at 5 DIV by examining the apoptotic effector caspase-3 and cell viability (ethidium monoazide exclusion) at 96 h following continuous exposure. Tat or morphine alone or in combination caused significant increases in GRP cell death at 96 h, but not at 24 h, following exposure. Although morphine or Tat caused increases in caspase-3 activity at 4 h, this was not accompanied with increased cleaved caspase-3 immunoreactive or ethidium monoazide-positive dying cells at 24 h. The results indicate that prolonged morphine or Tat exposure is intrinsically toxic to isolated GRPs and/or their progeny in vitro. Moreover, MOR and KOR are widely expressed by Sox2 and/or Nkx2.2-positive GRPs in vitro and the pattern of receptor expression appears to be developmentally regulated. The temporal requirement for prolonged morphine and HIV-1 Tat exposure to evoke toxicity in glia may coincide with the attainment of a particular stage of maturation and/or the development of particular apoptotic effector pathways and may be unique to spinal cord GRPs. Should similar patterns occur in vivo then we predict that immature astroglia and oligodendroglia may be preferentially vulnerable to HIV-1 infection or chronic opiate exposure.

Morphine Tolerance and Physical Dependence Are Altered in Conditional HIV-1 Tat Transgenic Mice

“…Cytotoxicity after prolonged morphine or Tat exposure has been previously demonstrated in vitro in glial-restricted precursors isolated from spinal cord (Buch et al, 2007). Interestingly, Tat did not affect tolerance to the effects of morphine in the locomotor activity assay, suggesting that Tat does not interact with morphine's actions at supraspinal sites governing locomotor activity including the striatum.…”

HIV‐1 alters neural and glial progenitor cell dynamics in the central nervous system: Coordinated response to opiates during maturation

“…After 5 d, cells were treated with Tat 1-86 (Clade B; 100 nM; ImmunoDiagnostics, Woburn, MA), ± morphine sulphate (500 nM; NIDA Drug Supply System, Rockville, MD), ± naloxone (1.5 μM; Sigma-Aldrich) for 12–48 h. Morphine, the major bioactive product of heroin in the brain, is a potent mu-opioid receptor (MOR) agonist; naloxone is a broad spectrum opioid receptor antagonist. These concentrations of Tat 1-86 and morphine have been established to elicit functional effects in glia and CNS progenitors in earlier studies (Buch et al 2007; El-Hage et al 2005; Hauser et al 2009; Khurdayan et al 2004). Naloxone was applied 30 min prior to other treatments, which were added simultaneously in pre-warmed medium.…”

“…Several studies suggest that CNS neural progenitor cells (NPCs), the undifferentiated precursors of both neurons and glia, are also susceptible to HIV-1 infection (Lawrence et al 2004; Rothenaigner et al 2007; Schwartz et al 2007). Even if NPCs are not readily infected, they may be affected by HIV-1 proteins directly (Buch et al 2007; Hahn et al 2010; Krathwohl and Kaiser 2004; Lee et al 2011; Mishra et al 2010; Okamoto et al 2007; Peng et al 2008), or secondarily by extracellular changes. NPCs are widely distributed in germinative zones during development.…”

“…NPCs and glial progenitors express functional opioid receptors in adult and neonatal rodent and human CNS (Buch et al 2007; Hauser et al 2009; Persson et al 2003; Reznikov et al 1999; Rius et al 1991; Tripathi et al 2008). Since co-exposure to opiate drugs of abuse enhances HIV-related CNS deficits in patients and experimental models (Anthony and Bell 2008; Bell et al 2006; Burdo et al 2006; Byrd et al 2011; Hauser et al 2007; Kopnisky et al 2007), we examined interactive opiate effects.…”

Interactive Comorbidity between Opioid Drug Abuse and HIV-1 Tat

“…Moreover, Tat-induced increases in inflammatory cytokines can intrinsically affect expression of opioid peptides and receptors in isolated astrocytes, 74 -76 leukocytes, [77][78][79] and in macrophages/microglia. 80,81 Importantly, such effects may not be restricted to Tat since gp120 and intact virions, can also alter opioid signaling through multiple mechanisms. 82 Thus, the response of the opioid system to HIV-1 infection is not restricted to a particular brain region, peptide family or receptor.…”