The hormone prolactin is a novel, endogenous trophic factor able to regulate reactive glia and to limit retinal degeneration

Abstract

Retinal degeneration is characterized by the progressive destruction of retinal cells, causing the deterioration and eventual loss of vision. We explored whether the hormone prolactin provides trophic support to retinal cells, thus protecting the retina from degenerative pressure. Inducing hyperprolactinemia limited photoreceptor apoptosis, gliosis, and changes in neurotrophin expression, and it preserved the photoresponse in the phototoxicity model of retinal degeneration, in which continuous exposure of rats to bright light leads to retinal cell death and retinal dysfunction. In this model, the expression levels of prolactin receptors in the retina were upregulated. Moreover, retinas from prolactin receptor-deficient mice exhibited photoresponsive dysfunction and gliosis that correlated with decreased levels of retinal bFGF, GDNF, and BDNF. Collectively, these data unveiled prolactin as a retinal trophic factor that may regulate glial-neuronal cell interactions and is a potential therapeutic molecule against retinal degeneration.

Keywords: gliosis; prolactin; retinal degeneration; trophic factor.

Figures

Figure 1.

Hyperprolactinemia prevents retinal cell apoptosis and photoresponsive dysfunction associated with light damage. A–F, Serum prolactin levels (A), retinal apoptosis (B), representative ERG responses under scotopic conditions (C), averaged amplitudes and implicit times of A- and B-waves under scotopic conditions (D), representative ERG responses under photopic conditions (E), and averaged amplitudes and implicit times of the photopic B-wave in sham and hyperprolactinemic (AP) rats exposed or not to BCL for 48 h (F). ERG analysis was performed on responses registered at maximal intensity stimulation (1.2 log cd.s/m2). Serum prolactin levels correspond to the mean ± SD of 4–14 animals per group. Other data correspond to the mean± SEM (n = 16–20 per group, three independent experiments; *p < 0.05, **p < 0.01, ***p < 0.001, and ****p < 0.0001, as indicated; two-way ANOVA with Bonferroni's post hoc test). n.s., Not significant; PRL, prolactin.

Figure 2.

Hyperprolactinemia protects against alterations of OPs caused by light damage. A, B, Representative OP recordings (A) and averaged OP amplitude and implicit time in response to the maximal light stimulus (1.2 log cd.s/m2) under scotopic conditions (B), in sham and hyperprolactinemic (AP) rats exposed or not exposed to BCL for 48 h. Data correspond to the mean ± SEM (n = 9–18 per group, three independent experiments; **p < 0.01 as indicated; two-way ANOVA with Bonferroni's post hoc test). OP1 to OP5 have been labeled as 1–5. n.s., Not significant.

Figure 3.

High levels of circulating prolactin limit retinal gliosis and neurotrophin expression changes associated with light damage, which upregulates the prolactin receptor in the retina. A, Quantitative PCR (qPCR)-based quantification of GFAP mRNA levels in retinas from sham and hyperprolactinemic (AP) rats exposed or not exposed to BCL for 48 h. The data are presented as the mean ± SEM (n = 4–9 per group, three independent experiments; **p < 0.01 as indicated; two-way ANOVA with Bonferroni's post hoc test). B, qPCR-based quantification of bFGF, NGF, GDNF, PEDF, CNTF, and BDNF mRNA levels in retinas from sham and hyperprolactinemic (AP) rats exposed or not exposed to BCL for 48 h. The data are presented as the mean ± SEM (n = 4–9 per group, three independent experiments; *p < 0.05, **p < 0.01, and ***p < 0.001 as indicated; two-way ANOVA with Bonferroni's post hoc test). C, qPCR-based quantification of prolactin receptor (PRL-R) mRNA levels in retinas from rats exposed or not exposed to BCL for 48 h. The data are presented as the mean ± SEM (n = 4–9 per group, three independent experiments; ***p < 0.001 as indicated, Student's t test).

Figure 4.

prlr−/− mice show photoresponsive dysfunction. A, B, Representative H&E-stained retinas (A) and averaged thickness of each layer of the retina (B) from prlr+/+and prlr−/− mice. Four sections per retina from each of six animals per group were analyzed in three separate experiments. Scale bar, 50 μm. C, Representative scotopic ERG response in prlr+/+, prlr+/−, and prlr−/− mice at 1.2 log cd.s/m2. D, Averaged amplitudes and implicit times of the scotopic A- and B-waves in prlr+/+, prlr+/−, and prlr−/− mice at increasing stimulus intensities. Data are presented as the mean ± SEM (n = 3–13 per group, seven independent experiments; *p < 0.05 vs values in prlr+/+ mice; one-way ANOVA with Bonferroni's post hoc test). E, Representative photopic ERG response in prlr+/+, prlr+/−, and prlr−/− mice. F, Averaged amplitude and implicit time of the photopic B-wave in prlr+/+, prlr+/−, and prlr−/− mice at 1.2 log cd.s/m2. Data are presented as the mean ± SEM (n = 3 per group, three independent experiments; *p < 0.05 as indicated; one-way ANOVA with Bonferroni's post hoc test). n.s., Not significant; ONL, outer nuclear layer; INL, inner nuclear layer; IPL, inner plexiform layer; OPL, outer plexiform layer; OS, outer segment; GCL, ganglion cell layer.

Figure 5.

prlr−/− mice show altered OPs. A, Representative OPs in prlr+/+, prlr+/−, and prlr−/− mice in response to the maximal light stimulus (1.2 log cd.s/m2). OP1–OP4 have been labeled from 1 to 4. B, Averaged OP amplitude in prlr+/+, prlr+/−, and prlr−/− mice at 1.2 log cd.s/m2. Data correspond to the mean ± SEM (n = 3 per group, three independent experiments; *p < 0.05 vs values for prlr−/− mice; one-way ANOVA with Bonferroni's post hoc test).

Figure 6.

Retinas from prlr−/− mice show decreased expression levels of bFGF, GDNF, and BDNF, and a tendency to increased gliosis. A, Retinal apoptosis from prlr+/+and prlr−/− mice. B, Quantitative PCR (qPCR)-based quantification of rhodopsin mRNA levels in retinas from prlr+/+, prlr+/−, and prlr−/− mice. Apoptosis data correspond to the mean ± SEM (n = 4 per group, two independent experiments. qPCR data correspond to the mean ± SEM (n = 4–9 per group; *p < 0.05 vs values for prlr+/+ mice; one-way ANOVA with Bonferroni's post hoc test). C, qPCR-based quantification of GFAP mRNA levels in retinas from prlr+/+, prlr+/−, and prlr−/− mice. The data are presented as the mean ± SEM (n = 4–9 per group, three independent experiments; *p < 0.05 vs values for prlr+/+ mice; one-way ANOVA with Bonferroni's post hoc test). D, qPCR-based quantification of bFGF, GDNF, BDNF, CNTF, PEDF, and NGF mRNA levels in retinas from prlr+/+, prlr+/−, and prlr−/− mice. The data are presented as the mean ± SEM (n = 4–9 per group, three independent experiments; **p < 0.01 and ***p < 0.001 vs values in prlr+/+ mice; one-way ANOVA with Bonferroni's post hoc test). n.s., Not significant.