Current Research

Effects of Prolactin on Rat Calvarial Bone Cells

 1. Background---Prolactin and the Signaling Pathway

  ♦ Prolactin, a pituitary hormone, is released in two forms, unmodified (U-      PRL) and phosphorylated (P-PRL). The amount of each released is physiologically regulated.

  ♦ Tumor-induced hyperprolactinemia is associated with osteopenia (reduced bone mass).

  ♦ Elevation of prolactin by neuroleptic drugs results in osteopenia.

  ♦ Prolonged lactation results in significant bone loss.

  ♦ Aging is correlated with increased prolactin and increased bone loss.

Fig. 1 Signaling Pathway of Prolactin

2. Previous Work from the Lab

♦ In our Lab, we have produced recombinant versions of each Prolactin. For the phosphorylated form, a molecular mimic in which the normally phosphorylated serine was replaced by an aspartate residue was produced.

    U-PRL, S179D-PRL(Pseudophosphorylated PRL, PP-PRL).

♦ Administration of extra S179D prolactin to pregnant mother rats to cause a delay in ossification of both calvarial bone and endochondral bone of developing pups.

♦ Which meant that at least some effects of prolactin were directly on oesteoblasts

♦ That both forms of prolactin inhibited oesteoblast alkaline phosphatase activity.

Fig. 2   Calvarial bone and digit cartilage/endochondral ossification in newborn rat pups in the 3 treatment groups.

          A and D: control pups (no exposure to additional PRL); B and E: tissues from pups exposed to wild-type PRL; and C and F: pups exposed to pseudophosphorylated (PP)-PRL.

         In the PP-PRL-exposed group was reduced endochondral ossification (Fig. 3, C and F). By contrast, administration of wild-type PRL had no obvious effect (Fig. 3, B and E).

Fig. 3   Effect of the recombinant PRLs on ALP activity of primary osteoblast cultures.

               A: Effects at low cell density; PP-PRL can inhibit ALP activity, but U-

                   PRL doesn’t have obvious effect on ALP  

                   activity. 

              B: Effects at high cell density.  Both prolactin can inhibit the activity of

                  Alkaline Phosphatase.

3. Goals of my Project and Research Results

A.   Goals----Using primary rat calvarial osteoblast

1)     To identify which genes related to bone growth are affected by prolactin (U-PRL and PP-PRL).

2)     When identified, to determine how prolactin regulates these genes (molecular mechanisms).

                                      Table 1 Genes which have been examined

4. Results from my Experiments

♦ Both prolactins inhibit alkaline phosphatase expression.  

♦ PP-PRL can increase BMP4. In contrast, U-PRL doesn’t affect BMP4. 

♦  Both prolactins have no obvious effect  on rVDR, rOPN and rOC. 

♦ U-PRL can inhibit Estrogen Receptor α and Estrogen Receptor β. But, PP-PRL doesn’t affect them.

According to the results above, changes in all 4 identified prolactin-responsive genes are consistent with an osteopenic role for prolactin.

Curriculum Vitae