Influence of FGF23 and Klotho on male reproduction: Systemic vs direct effects

Currently, no treatment exists to improve semen quality in most infertile men. Here, we demonstrate systemic and direct effects of Fibroblast growth factor 23 (FGF23) and Klotho, which normally regulate vitamin D and mineral homeostasis, on testicular function. Direct effects are plausible because KLOTHO is expressed in both germ cells and spermatozoa and forms with FGFR1 a specific receptor for the bone-derived hormone FGF23. Treatment with FGF23 increased testicular weight in wild-type mice, while mice with global loss of either FGF23 or Klotho had low testicular weight, reduced sperm count, and sperm motility. Mice with germ cell-specific Klotho (gcKL) deficiency neither had a change in sperm count nor sperm motility. However, a tendency toward fewer pregnancies was detected, and significantly fewer Klotho heterozygous pups originated from gcKL knockdown mice than would be expected by mendelian inheritance. Moreover, gcKL mice had a molecular phenotype with higher testicular expression of Slc34a2 and Trpv5 than wild-type littermates, which suggests a regulatory role for testicular phosphate and calcium homeostasis. KLOTHO and FGFR1 were also expressed in human germ cells and spermatozoa, and FGF23 treatment augmented the calcium response to progesterone in human spermatozoa. Moreover, cross-sectional data revealed that infertile men with the highest serum Klotho levels had significantly higher serum Inhibin B and total sperm count than men with the lowest serum Klotho concentrations. In conclusion, this translational study suggests that FGF23 and Klotho influence gonadal function and testicular mineral ion homeostasis both directly and indirectly through systemic changes in vitamin D and mineral homeostasis.

Effects of klotho deletion from bone during chronic kidney disease

Klotho is a type I transmembrane protein that acts as a permissive co-receptor for FGF23 and helps to maintain proper mineral metabolism. Mice carrying a loss-of-function mutation in either the Klotho or Fgf23 gene develop many similar phenotypes including osteoporosis. Based on these observations it was hypothesized that the bone phenotypes in Klotho- and Fgf23-null mice may be mediated through a common signaling pathway. Recent improvements in antibody specificity have shown that osteoblasts and osteocytes, which produce FGF23, also express low amount of membrane Klotho. But, the role of Klotho in bone is still largely unclear. In this review we summarize the literature and show that Klotho has an FGF23 dependent and independent effect in bone.

Klotho expression in long bones regulates FGF23 production during renal failure

Circulating levels of bone-derived fibroblast growth factor 23 (FGF23) increase early during acute and chronic kidney disease and are associated with adverse outcomes. Membrane-bound Klotho acts as a permissive coreceptor for FGF23, and its expression was recently found in osteoblasts/osteocytes. We hypothesized that Klotho in bone cells is part of an autocrine feedback loop that regulates FGF23 expression during renal failure. Thus, we induced renal failure in mice with targeted deletion of Klotho in long bones. Uremic wild-type (KL^fl/fl ) and knockout (Prx1-Cre;KL^fl/fl ) mice both responded with reduced body weight, kidney atrophy, hyperphosphatemia, and increased bone turnover. Importantly, long bones of Prx1-Cre;KL^fl/fl mice but not their axial skeleton failed to increase FGF23 expression as observed in uremic KL^fl/fl mice. Consequently, Prx1-Cre;KL^fl/fl mice had significantly lower serum FGF23 and parathyroid hormone levels, and higher renal 1-α-hydroxylase expression, serum 1,25-dihydroxyvitamin D, and calcium levels than KL^fl/fl mice. These results were confirmed in two independent models of renal failure, adenine diet induced and 5/6 nephrectomy. Moreover, FGF23-treated bone cells required Klotho to increase FGF23 mRNA and ERK phosphorylation. In summary, our novel findings show that Klotho in bone is crucial for inducing FGF23 production upon renal failure. We propose the presence of an autocrine feedback loop in which Klotho senses the need for FGF23.-Kaludjerovic, J., Komaba, H., Sato, T., Erben, R. G., Baron, R., Olauson, H., Larsson, T. E., Lanske, B. Klotho expression in long bones regulates FGF23 production during renal failure.

A Mouse Model for Studying Nutritional Programming: Effects of Early Life Exposure to Soy Isoflavones on Bone and Reproductive Health

Over the past decade, our research group has characterized and used a mouse model to demonstrate that "nutritional programming" of bone development occurs when mice receive soy isoflavones (ISO) during the first days of life. Nutritional programming of bone development can be defined as the ability for diet during early life to set a trajectory for better or compromised bone health at adulthood. We have shown that CD-1 mice exposed to soy ISO during early neonatal life have higher bone mineral density (BMD) and greater trabecular inter-connectivity in long bones and lumbar spine at young adulthood. These skeletal sites also withstand greater forces before fracture. Because the chemical structure of ISO resembles that of 17-β-estradiol and can bind to estrogen receptors in reproductive tissues, it was prudent to expand analyses to include measures of reproductive health. This review highlights aspects of our studies in CD-1 mice to understand the early life programming effects of soy ISO on bone and reproductive health. Preclinical mouse models can provide useful data to help develop and guide the design of studies in human cohorts, which may, depending on findings and considerations of safety, lead to dietary interventions that optimize bone health.

Bone-specific gene expression patterns and whole bone tissue of female mice are programmed by early life exposure to soy isoflavones and folic acid

Female mice exposed to soy isoflavones (ISO) during early postnatal life have improved bone outcomes at adulthood. Since long-lasting effects may be mediated by DNA methylation, we hypothesized that providing supplemental folic acid (FA), a methyl donor, during early life, would enhance the positive effect of ISO to bone health. Bone-specific gene expression patterns were studied to understand potential mechanisms. CD-1 dams (n=36) were randomized to adequate or supplemental levels of FA (2 or 8 mg/kg diet) during pregnancy and lactation, and offspring received corn oil or ISO (7 mg/kg body weight/d) from postnatal day 1 to 10. From weaning, pups were fed an adequate FA diet and were studied to 4 months of age. Female offspring exposed to supplemental FA+ISO had higher bone mineral density (BMD), trabecular connectivity and peak load at the lumbar spine compared to females exposed to adequate FA. Female offspring exposed to adequate FA+ISO or supplemental FA had higher (P<.05) BMD and greater resistance to fracture at the lumbar spine and the femur; higher trabecular connectivity at the lumbar spine; and lower expression of DNA methyltransferase 3a (Dnmt3a) and neuropeptide Y (NPY) in the femur compared to mice exposed to adequate FA. In addition, only mice exposed to adequate FA+ISO had microstructural improvements at the femur neck and higher serum osteoprotegrin (OPG) and insulin growth factor-I (IGF-I). In summary, exposure to supplemental FA did not enhance the positive effect of ISO in bone. However, exposure to adequate FA+ISO or supplemental FA improved bone at least in part by suppressing Dnmt3a and NPY.

Adequate but not supplemental folic acid combined with soy isoflavones during early life improves bone health at adulthood in male mice

Previous investigations from our laboratory have demonstrated that neonatal exposure to soy isoflavones (ISO) improves bone outcomes in CD-1 mice at adulthood with greater benefits in females than males. This study determined whether early-life exposure to supplemental folic acid (FA) - that may enhance DNA methylation of target genes - in combination with ISO provides greater benefits to male bone development than ISO alone. CD-1 dams were randomized to a low (0 mg/kg diet), adequate (2 mg/kg diet) or supplemental (8 mg/kg diet) level of FA during pregnancy and lactation. Offspring received corn oil or ISO (7 mg/kg of body weight per day) from postnatal day 1-10. From weaning, males were fed adequate FA and studied to age 4 months. Offspring exposed to adequate FA+ISO had multiple benefits to bone health: higher (P<.05) bone mineral density (BMD) and greater (P<.05) resistance to fracture at the femur and lumbar spine than mice exposed to adequate FA alone. Exposure to supplemental FA+ISO resulted in higher (P<.05) serum osteoprotegerin (OPG), and a higher ratio of OPG to receptor activator for nuclear factor κβ ligand (RANKL) but did not result in greater BMD or strength at the femur or lumbar spine than supplemental FA alone. In conclusion, early-life exposure to adequate FA+ISO provided functional benefits to male bone development, while improvements induced by supplemental FA+ISO were limited to a higher level of serum OPG. Mechanistic studies are needed to better understand how FA and ISO improve bone development in male offspring.

Early life exposure to genistein and daidzein disrupts structural development of reproductive organs in female mice

In mice, exposure to isoflavones (ISO), abundant in soy infant formula, during the first 5 d of life alters structural and functional development of reproductive organs. Effects of longer exposures are unknown. The study objective was to evaluate whether exposure to a combination of daidzein and genistein in the first 10 compared to 5 d of life results in greater adverse effects on ovarian and uterine structure in adult mice. Thirteen litters of 8-12 pups were cross-fostered and randomized to corn oil or ISO (2 mg daidzein + 5 mg genistein/kg body weight/d) for the first 5 or 10 d of life. The 10-d protocol mimicked the period when infants are fed soy protein formula (SPF) but avoids the time when suckling pups can consume mother's diet. Body and organ weights, and histology of ovaries and uteri were analyzed. There were no differences in the ovary or uterus weight, number of ovarian follicles, number of multiple oocyte follicles, or percent of ovarian cysts with 5 or 10 d ISO intervention compared to respective controls. The 10-d ISO group had higher body weights from 6 d to 4 mo of age and a higher percent of hyperplasia in the oviduct than the respective control. Lower number of ovarian corpus lutea and a higher incidence of abnormal changes were reported in the uteri of both ISO groups compared to their respective controls. Five and 10-d exposure to ISO had similar long-lasting adverse effects on the structure of ovaries and uterus in adult mice. Only the 10-d ISO exposure resulted in greater body weight gain at adulthood.

Neonatal administration of isoflavones attenuates deterioration of bone tissue in female but not male mice

Neonatal exposure to soy isoflavones at levels similar to that of infants fed soy protein formula resulted in higher bone mineral density (BMD), improved bone structure, and greater bone strength at young adulthood in female CD-1 mice (1,2). Our objective in this study was to determine whether these improvements in bone quantity and quality at 4 mo of age provide protection against the deterioration of bone tissue that occurs after a decline in endogenous sex steroid production. Male and female CD-1 mice (n = 8-18 pups per group per gender) were randomized to subcutaneous injections of corn oil [negative control (CON)], daidzein + genistein (DG; 7 mg x kg body weight(-1) x d(-1)), or diethylstilbestrol [(DES); positive control, 2 mg x kg body weight(-1) x d(-1)) from postnatal d 1 to 5. At 4 mo of age, mice were ovariectomized (females) or orchidectomized (males) and studied to 8 mo of age. Females treated with DG had higher (P < 0.05) femur and vertebral bone mineral content (BMC) and BMD compared with the CON group. Microstructural analysis revealed that improvements in BMD induced by DG and DES were coupled with greater trabecular thickness at the lumbar spine. Importantly, structural improvements resulted in bones that were more resistant to fracture, as the peak load of the femoral midpoint and lumbar vertebra 2 were higher (P < 0.05) with DG compared with CON. Effects in males were not significant. In conclusion, short-term neonatal exposure to isoflavones provides protection against the deterioration of bone tissue in females but not males after a decline of endogenous sex steroid production.

Neonatal exposure to daidzein, genistein, or the combination modulates bone development in female CD-1 mice

Neonatal exposure to genistein (GEN), an isoflavone abundant in soy, favorably modulates bone mineral density (BMD) and bone strength in mice at adulthood. The study objective was to determine whether early exposure to a combination of the soy isoflavones daidzein (DAI) and GEN that naturally exists in soy protein-based infant formula results in greater benefits to bone at adulthood than either treatment alone. Male and female CD-1 mice (n = 8-16 pups per group per gender) were randomized to subcutaneous injections of DAI (2 mg x kg body weight(-1) x d(-1)), GEN (5 mg x kg body weight(-1) x d(-1)), DAI+GEN (7 mg x kg body weight(-1) x d(-1)), diethylstilbesterol (DES; positive control) (2 mg x kg body weight(-1) x d(-1)), or control (CON) from postnatal d 1-5 and were studied to 4 mo of age. BMD, biomechanical bone strength, and bone microarchitecture were assessed at the femur and lumbar vertebrae (LV). Females treated with DAI, GEN, DAI+GEN, or DES had greater (P < 0.05) BMD at the LV compared with CON and vertebra in the DAI and DES group were more resistant to compression fractures. Microstructural analyses demonstrated that treatment with DAI and GEN resulted in greater (P < 0.05) trabecular connectivity and trabecular thickness, respectively, than the CON. In conclusion, neonatal exposure to DAI and/or GEN had a positive effect on the skeleton of female mice at adulthood, but, compared with individual treatments, DAI+GEN did not have a greater benefit to bone in females or males.

Adiponectin is a negative regulator of bone mineral and bone strength in growing mice

Obesity is associated with increased bone mineral density (BMD) but the mechanism for this is unclear. Serum levels of the adipokine adiponectin are inversely correlated with obesity, but results from studies on its relationship to bone mass are conflicting. The objective of this study was to compare bone mineral content (BMC), BMD and biomechanical strength properties of femur and lumbar vertebrae in 8- and 16-week old adiponectin transgenic mice (AdTg). These mice exhibit significantly elevated circulating adiponectin but have similar body weights compared to wild-type (WT) littermates that were used as controls. Female AdTg mice displayed significantly lower femur BMC at 8 and 16 weeks of age and femur neck peak load was significantly lower in 8-week old AdTg mice of both genders compared to controls. The peak load from compression testing of an individual lumbar vertebra was significantly lower in female AdTg mice compared to WT at 8 weeks, and this difference persisted at 16 weeks of age. In addition, lumbar vertebrae BMC was significantly lower in 16-week old male AdTg mice compared to WT although vertebra peak load was not different. Serum adiponectin levels were inversely correlated with femur BMC. In summary, elevated circulating adiponectin inhibits the acquisition of bone mass in growing mice and results in decreased biomechanical measures of functional strength that are surrogate measures of susceptibility to fractures. These results support a role for circulating adiponectin as a metabolic link that can explain, at least in part, the positive relationship between obesity and both bone mass and reduced susceptibility to fractures.

Diethylstilbesterol has gender-specific effects on weight gain and bone development in mice

Neonatal exposure to diethylstilbesterol (DES) in female mice programs estrogen-sensitive tissues, resulting in greater body weight gain and positive effects on bone architecture at adulthood. Using the CD-1 mouse model, the objective of the present study was to examine how short-term neonatal exposure to DES modulates weight gain as well as bone mineral density (BMD), bone strength, and bone microarchitecture in both males and females at adulthood. Male and female offspring (n = 8-12 pups/treatment/gender) were randomized to DES (2 mg/kg bw/d) or control (corn oil) from postnatal day 1 to 5 (subcutaneous injection, once daily) and sacrificed at 4 mo of age. Body weight was measured weekly, while bone mineral, strength, and microarchitecture were measured at 4 mo of age. DES treatment resulted in significantly higher body weight in females but lower weight in males at 4 mo of age. In DES-treated females, markedly higher BMD of lumbar vertebrae (LV1-LV3) was translated into significantly stronger LV2 that was more resistant to fracture; similar effects were observed at the femur midpoint. At the spine, males had a markedly lower BMD and peak load, suggesting an adverse effect. Microstructural analyses demonstrated that functional changes in femurs, i.e., peak load, were primarily due to modulation of cortical bone. In conclusion, neonatal exposure to DES exerted gender-specific effects on body weight gain and bone health.