Evidence for Direct Effects of Prolactin on Human Osteoblasts: Inhibition-of Cell Growth and Mineralization

Hyperprolactinemia is one of the risk factor of decrease in bone mass which has been believed to be mediated by hypogonadism. However, the presence of prolactin receptor in human osteosarcoma cell line and primary bone cell culture from mouse calvariae supported the hypothesis of a direct prolactin (PRL) action on bone cells. Therefore, the aim of this study was to investigate the role of PRL and its signal transduction pathway in the regulation of bone metabolism via osteoblast differentiation. Human pre-osteoblasts (SV-HFO) that differentiate in a 3-week period from proliferating pre-osteoblasts (days 2-7) to extracellular matrix producing cells (days 7-14) which is eventually mineralized (days 14-21) were used. Concentration of PRL mimicked a lactating period (100 ng/ml) was used to incubate SV-HFO for 21 days in osteogenic medium. Human prolactin receptor mRNA and protein are expressed in SV-HFO. PRL significantly decreased osteoblast number (DNA content) which was due to a decrease in proliferation. PRL increased osteogenic markers, RUNX2 and ALP in early stage of osteoblast differentiation while decreasing it later suggesting a bi-directional effect. Calcium measurement and Alizarin red staining showed a reduction of mineralization by PRL while having neither an effect on osteoblast activity nor RANKL/OPG mRNA ratio. We also demonstrated that PRL action on mineralization was not via PI-3 kinase pathway. The present study provides evidence of a direct effect of prolactin on osteoblast differentiation and in vitro mineralization. J. Cell. Biochem. 107: 677-685, 2009. (C) 2009 Wiley-Liss, Inc

Deletion of Zfp521 rescues the growth plate phenotype in a mouse model of Jansen metaphyseal chondrodysplasia

Jansen metaphyseal chondrodysplasia (JMC) is caused by a constitutively activating mutation of the parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor (PTHR1) and is characterized by widening of the metaphyses, reduction of long bone length, and short stature. A transgenic mouse expressing this mutation under the collagen α1(II) promoter has been generated to investigate the mechanisms responsible for this chondrodysplasia. We recently identified zinc finger protein 521 (Zfp521) as a downstream target gene of PTHrP signaling. Interestingly, loss of Zfp521 from chondrocytes leads to reduced cell proliferation and increased differentiation in the growth plate. Thus, we hypothesized that specifically ablating Zfp521 from Jansen chondrocytes could sufficiently rescue the chondrodysplasia phenotype. Our results show that Zfp521 expression is up-regulated in Jansen mouse growth plate chondrocytes and that PTHR1 is required for Zfp521 expression. Its ablation from Jansen chondrocytes restored normal cell differentiation, thus initiating chondrocyte apoptosis at the chondro-osseous junction, leading to partial rescue of endochondral bone formation shown by proper bone length. This study provides the first genetic evidence that Zfp521 is required downstream of PTHR1 signaling to act on chondrocyte proliferation, differentiation, and cell death.—Seriwatanachai, D., Densmore, M. J., Sato, T., Correa, D., Neff, L., Baron, R., Lanske, B. Deletion of Zfp521 rescues the growth plate phenotype in a mouse model of Jansen metaphyseal chondrodysplasia

Prolactin Expression in the Cochlea of Aged BALB/c Mice Is Gender Biased and Correlates to Loss of Bone Mineral Density and Hearing Loss

Prolactin is a versatile hormone with over 300 known functions and predominantly expressed in the pituitary. However, its expression has additionally been found in a number of extrapituitary organs. Recently, we described the expression of prolactin in the inner ear of mice, where it was correlated to age. Previous research has shown prolactin to be linked to abnormal bone metabolism and hearing loss due to changes in morphology of the bony otic capsule. Here we further investigated the relationship between prolactin, hearing loss and cochlea bone metabolism. BALB/c mice were tested for hearing using ABR at 6 and 12 months of age. Bone mineral density of the cochlea was evaluated using microCT scanning. Prolactin expression was calculated using quantitative real time PCR. Expression of the key regulators of bone metabolism, osteoprotegerin and receptor activator of nuclear factor-kappaB ligand were also determined. We found that prolactin expression was exclusive to the female mice. This also correlated to a greater threshold shift in hearing for the females between 6 and 12 months of age. Analyses of the cochlea also show that the bone mineral density was lower in females compared to males. However, no gender differences in expression of osteoprotegerin or receptor activator of nuclear factor-kappaB ligand could be found. Further analysis of cochlea histological sections revealed larger ostocyte lacunae in the females. These results provide a possible mechanism for an age related hearing loss sub-type that is associated with gender and provides clues as to how this gender bias in hearing loss develops. In addition, it has the potential to lead to treatment for this specific type of hearing loss

Bone Remodeling, Bone Mass and Weight Gain in Patients with Stabilized Schizophrenia in Real-Life Conditions Treated with Long-Acting Injectable Risperidone

Background: Prolactin-raising antipsychotics, risperidone (antidopaminergic activity), may be associated with low bone mass. On the other hand, risperidone may cause an increase in body weight thought to be favorable for bone. Objectives: (1) To determine bone remodeling parameters and bone mass in patients with schizophrenia on long-term treatment with long-acting injectable risperidone (LAIR) in naturalistic settings, and (2) to evaluate the change in body weight, metabolic profile and neuroendocrine status in these patients. Design: This was a prospective, cross-sectional study. Patients: Patients included 26 outpatients with controlled schizophrenia in real-life conditions (age 31.3 +/- 1.3 years, BMI 28.1 +/- 1.0) on long-term maintenance therapy with LAIR for a mean of 18.0 +/- 1.6 months (range 6-36) with a mean dose of 38 +/- 2 mg. 35 subjects matched for sex, age, BMI and education served as healthy controls. Methods: Serum osteocalcin, C-terminal telopeptide of type I collagen (CTx), vitamin D, leptin, prolactin, sex steroids, and parathyroid hormone were assessed. Indices of insulin sensitivity and resistance were determined following an oral glucose tolerance test (OGTT). Bone mineral density (BMD) was measured by dual X-ray absorptiometry at the lumbar spine (LS) and femoral neck (FN). Results: Mild to moderate hyperprolactinemia (1,000-2,000 mU/l) was associated with asymptomatic hypogonadism. Prolactin values >2,000 mU/l occurred in a few female patients. Hypogonadism leads to a slight increase (upper limit of normal) in bone resorption marker (CTx) in patients with schizophrenia (p = 0.023). As for bone mass, although lower at the spine than in healthy subjects, it did not reach statistical significance (p = 0.094), while at the FN, BMD was not different from healthy subjects. Body weight increased on average 8.7 +/- 1.6 kg in more than 50% of patients. Leptin levels adjusted for BMI in females were significantly higher in patients than in healthy female subjects (p = 0.018), while in males there was no difference between the groups (p = 0.833). A high prevalence of low vitamin D levels and more current smokers were found in patients with schizophrenia. As for the metabolic profile during treatment with risperidone, the low Matsuda index of insulin sensitivity (p = 0.039) confirmed insulin resistance in these patients. Conclusion: A potential long-term consequence of asymptomatic hypogonadism due to risperidone-induced hyperprolactinemia might cause a slight rise in bone resorption marker (CTx). On the other hand, by increasing body weight, risperidone could have a protective effect on the bone and thus no change in bone mass was recorded when compared with healthy controls