Activation of Sigma Receptors With Afobazole Modulates Microglial, but Not Neuronal, Apoptotic Gene Expression in Response to Long-Term Ischemia Exposure

Abstract

Stroke continues to be a leading cause of death and serious long-term disability. The lack of therapeutic options for treating stroke at delayed time points (≥6 h post-stroke) remains a challenge. The sigma receptor agonist, afobazole, an anxiolytic used clinically in Russia, has been shown to reduce neuronal and glial cell injury following ischemia and acidosis; both of which have been shown to play important roles following an ischemic stroke. However, the mechanism(s) responsible for this cytoprotection remain unknown. Experiments were carried out on isolated microglia from neonatal rats and cortical neurons from embryonic rats to gain further insight into these mechanisms. Prolonged exposure to in vitro ischemia resulted in microglial cell death, which was associated with increased expression of the pro-apoptotic protein, Bax, the death protease, caspase-3, and reduced expression in the anti-apoptotic protein Bcl-2. Incubation of cells with afobazole during ischemia decreased the number of microglia expressing both Bax and caspase-3, and increased cells expressing Bcl-2, which resulted in a concomitant enhancement in cell survival. In similar experiments, incubation of neurons under in vitro ischemic conditions resulted in higher expression of Bax and caspase-3, while at the same time expression of Bcl-2 was decreased. However, unlike observations made in microglial cells, afobazole was unable to modulate the expression of these apoptotic proteins, but a reduction in neuronal death was still noted. The functional state of surviving neurons was assessed by measuring metabolic activity, resting membrane potential, and responses to membrane depolarizations. Results showed that these neurons maintained membrane potential but had low metabolic activity and were unresponsive to membrane depolarizations. However, while these neurons were not fully functional, there was significant protection by afobazole against long-term ischemia-induced cell death. Thus, the effects of sigma receptor activation on microglial and neuronal responses to ischemia differ significantly.

Multi-Target Directed Ligands (MTDLs) Binding the σ1 Receptor as Promising Therapeutics: State of the Art and Perspectives

“…Therefore, the inhibition of GSK3β and CDK/p25 by AF710B, upon interaction with both M1 and σ 1 receptors, results as a promising approach in the treatment of tauopathies [82]. The effect of σ 1 receptors in inflammation through microglia modulation has been reported [54,86,87], and AF710B was shown to reduce reactive astrocytes and activated microglia in the animals, as detected by the low levels of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba-1). Notably, astrocytes and microglia are increased in number and size in AD patients.…”

Chaperone-Dependent Mechanisms as a Pharmacological Target for Neuroprotection

“…The anxiolytic afobazole, a Sigma1R ligand with agonist-like actions [269,366,367], introduced into medical practice in Russia, exhibits cytoprotective and neuroprotective properties in a number of experimental models [368][369][370][371][372][373][374][375][376][377][378][379][380] (Table S1).…”

The Sigma‐2 Receptor/TMEM97 Agonist PB28 Suppresses Cell Proliferation and Invasion by Regulating the PI3K‐AKT‐mTOR Signalling Pathway in Renal Cancer

“… 2 , 3 The sigma receptor has been of interest since its discovery due to its wide range of biological functions, and it is considered to play significant roles in regulating cell survival, morphology and differentiation. 4 , 5 It has gradually become a target for cancer diagnosis and treatment. 6 , 7 , 8 , 9 The sigma‐2 receptor is an 18–21 kD membrane protein, 2 and recent receptor‐ligand binding assays have shown that it is highly expressed in the liver and kidney of rabbits.…”