Differential responses of progesterone receptor membrane component-1 (Pgrmc1) and the classical progesterone receptor (Pgr) to 17β-estradiol and progesterone in hippocampal subregions that support synaptic remodeling and neurogenesis

Abstract

Progesterone (P4) and estradiol (E2) modulate neurogenesis and synaptic remodeling in the hippocampus during the rat estrous cycle and in response to deafferenting lesions, but little is known about the steroidal regulation of hippocampal progesterone receptors associated with these processes. We examined the neuronal expression of progesterone receptor membrane component-1 (Pgrmc1) and the classical progesterone receptor (Pgr), by in situ hybridization and immunohistochemistry. Pgr, a transcription factor, has been associated with synaptic remodeling and other major actions of P4, whereas Pgrmc1 is implicated in P4-dependent proliferation of adult neuroprogenitor cells and with rapid P4 effects on membranes. Ovariectomized adult rats were given E2, P4, or E2+P4 on two schedules: a 4-d model of the rodent estrous cycle and a 30-d model of postmenopausal hormone therapy. Pgr was hormonally responsive only in CA1 pyramidal neurons, and the induction of Pgr by E2 was partly antagonized by P4 only on the 30-d schedule. In CA3 pyramidal and dentate gyrus (DG) neurons, Pgr was largely unresponsive to all hormone treatments. In contrast to Pgr, Pgrmc1 was generally induced by E2 and/or P4 throughout the hippocampus in CA1, CA3, and DG neurons. In neuroprogenitor cells of the DG (immunopositive for bromodeoxyuridine and doublecortin), both Pgrmc1 and Pgr were detected. The differential regulation of hippocampal Pgrmc1 and Pgr by E2 and P4 may guide drug development in hormonal therapy for support of neurogenesis and synaptic regeneration.

Fig. 1.

Two hormone replacement schedules were studied. A, For 4-d hormone replacement, rats (n = 6 rats per group) were given two injections of E2 (10 μg, sc), 24 h apart, followed by single P4 injection (4 mg/kg, sc) 24 h after last E2 injection. A single injection of BrdU (100 mg/kg, ip) was given 1 h after P4; tissue collection, 30 h after BrdU. B, For 30-d hormone replacement, rats (n = 5 rats per group) were implanted with E2 pellet (0.72 mg/30 d release) 2 wk after OVX, followed by P4 pellet (50 mg/15 d release) in the last 10 d; tissue collection on d 30.

Fig. 2.

Expression of Pgrmc1 and Pgr in hippocampal neuronal layers. A, Autoradiographic film images showed differential distribution of mRNA for Pgrmc1 (left) and Pgr (right) in hippocampal neuronal layers. Pgrmc1 was prevalent across all three neuronal layers. By contrast, Pgr mRNA was prevalent in CA1 and CA3 pyramidal neurons, but it was barely detected in adjacent DG neurons. B, Average grain density for Pgrmc1 and Pgr in individual neurons of CA1 (100 cells per rat), CA3 (100 cells per rat), and DG (120 cells per rat). Pgrmc1 grain density was similar in CA1 and CA3 neuronal perikarya and far below in DG neurons. *, P < 0.01 vs. CA1 and CA3. More than 80% neurons in CA1, CA3, and DG were positive for Pgrmc1 mRNA. CA3 neurons had 2-fold more Pgr mRNA/perikaryon than CA1 and DG neurons. CA1 neurons had 2-fold Pgr over DG neurons. More than 80% CA1 and CA3 neurons, but only approximately 25% DG neurons were positive for Pgr mRNA. **, P < 0.0001 vs. other groups. C, Immunohistochemistry for Pgrmc1 and Pgr showed similar protein expression of both receptors as mRNA. Scale bars, 100 μm. Avg., Average.

Fig. 3.

Regulation of Pgrmc1 and Pgr mRNA by E2 and P4. A, Pgrmc1 mRNA was increased by E2, P4, and E2+P4 in CA1, CA3, and DG neurons after both 4-d (n = 6 rats/group) and 30-d hormone replacement schedules (n = 5 rats per group). *, P < 0.03 compared with respective OVX. B, In CA1 neurons Pgr mRNA was increased by E2, P4, and E2+P4 on the 4-d schedule, and by E2 or P4 alone on the 30-d schedule. Modest increase in Pgr mRNA was also seen in CA3 neurons by P4 (P4 alone and E2+P4 group) only on the 4-d schedule. Pgr mRNA did not respond to either the 4-d or 30-d schedule in DG neurons. **, P < 0.01 vs. OVX in CA1. ^, P < 0.01 compared with 4-d schedule in CA1. *, P < 0.05, vs. OVX in CA3 neurons.

Fig. 4.

Expression of Pgrmc1 and Pgr in NPC. A and B, Colocalization of Pgrmc1 and Pgr in replicating (BrdU) NPC by double immunohistochemistry for Pgrmc1 with BrdU (A) and Pgr with BrdU (B); individual colabeled cell magnified in inset. C and D, Double immunohistochemistry for Pgrmc1 (C) with Doublecortin (DCX), a marker of newly generated neurons in SGZ of DG and Pgr (D) with DCX showed colocalization of both in DCX-positive newly generated neurons; individual colabeled cell magnified in inset. Scale bars, 20 μm. E, Hormonal regulation of neurogenesis by E2 and P4 in the DG subgranular zone. Both E2 and P4 (4-d schedule; n = 6 rats per group) increased the number of BrdU⁺ cells in SGZ; response to E2+P4 was slightly lower (P = 0.15; not significant). *, P < 0.03, vs. OVX. Avg., Average.