Progesterone Influence on Neurite Outgrowth Involves Microglia

Abstract

Progesterone (P4) antagonizes estradiol (E2) in synaptic remodeling in the hippocampus during the rat estrous cycle. To further understand how P4 modulates synaptic plasticity, we used entorhinal cortex lesions, which induce E2-dependent neurite sprouting in the hippocampus. In young ovariectomized rats, the E2-dependent entorhinal cortex lesion-induced sprouting was attenuated by concurrent treatment with P4 and E2. Microglial activation also showed the E2-P4 antagonism. These findings extend reports on the estrous cycle synaptic remodeling without lesions by showing the P4-E2 antagonism during simultaneous treatment with both E2 and P4. Glial mechanisms were analyzed with the wounding-in-a-dish model of cocultured glia and embryonic d-18 cortical neurons from rat. In cocultures of mixed glia (astrocytes plus 30% microglia), P4 antagonized the E2-dependent neurite outgrowth (number and length) and neuron viability in the presence of E2, as observed in vivo. However, removal of microglia (astrocyte-neuron coculture) abolished the antagonism of E2 by P4 on neuron sprouting. The P4 receptor antagonists ORG-31710 and RU-486 blocked the antagonism of P4 on E2-dependent sprouting. These findings suggest a new role for microglia in P4 antagonism of E2 in neuronal plasticity and show its dependence on progesterone receptors. These findings are also relevant to the inclusion of progestins in hormone therapy, which is controversial in relation to cognitive declines during aging and in Alzheimer's disease.

Progesterone Antagonism of Neurite Outgrowth Depends on Microglial Activation via Pgrmc1/S2R

“…Cell cultures were characterized by immunocytochemistry (ICC) using cell-specific markers for astrocytes glial fibrillary acidic protein (GFAP) and microglia (IBA1 and CD11b). Primary cultures of mixed glia contain microglia and astrocytes (dilution 1:3), whereas enriched astrocyte and microglia cultures are 95% monotypic (2). Enriched astrocyte, enriched microglia, or mixed glia cultures were plated in poly-d-lysine-coated 4-chamber glass slides (Nunc Lab-Tek II Chamber Slide System; Thermo Scientific, Rochester, New York) at 2 ϫ 10 5 cells per well for mixed glia.…”

“…For add-back experiments, E18 neurons were plated 6 hours after the add-back of either microglia or astrocytes. The cocultures were grown for 3 days before scratch wounding (2). Scratch wounding employed a grid-template with intersecting lines of 1 cm each that were inscribed with a plastic pipette tip (1 mm diameter), yielding 2 traces per well, which induced consistent cell responses across experiments (2).…”

“…The P4 antagonism of E2-dependent neurite outgrowth was blocked by the drugs ORG-31710 and RU-486, which have specificity for Pgr, the classical DNA-binding Pgr. However, the P4-E2 antagonism of neurite outgrowth was observed only in coculture with mixed glia (1:3 microglia to astrocytes), but not in enriched astrocytes from which microglia were removed (2). This result was puzzling because Pgr was not detected in microglia (4).…”

“…Neuronal sprouting in response to axotomy is also modulated by P4-E2 antagonism. In an adult rat model of entorhinal cortex lesions that axotomize the perforant pathway to the hippocampus, the ensuing compensatory neurite outgrowth into the dentate gyrus molecular layer was stimulated by E2 and blocked by concurrent administration of E2ϩP4 (2). Astrocyte and microglial activation in the deafferented zone was correspondingly modulated by E2 and P4.…”

Aberrant gastrocnemius muscle innervation by tibial nerve afferents after implantation of chitosan tubes impregnated with progesterone favored locomotion recovery in rats with transected sciatic nerve

“…Adequate locomotion depends on the formation of reliable muscle synergy. 17,18 Thus, the regulation of axon sprouting by progesterone 58 induces aberrant sprouting, 11 which in turn produces muscle synergy, with compensatory muscle activation among extensor, flexor, and bifunctional muscles, and restores hindlimb movements for adequate locomotion. 16,24 However, in prolonged axotomized neurons a better outcome seems possible when distal and proximal ends are sutured to nearby muscles, which are later bridged with chitosan tubes.…”