The Human TSHβ Subunit Proteins and Their Binding Sites on the TSH Receptor Using Molecular Dynamics Simulation

To gain further insight into the binding of the normal and variant human TSHβ subunits (TSHβ and TSHβv), we modeled the 2 monomeric proteins and studied their interaction with the TSH receptor ectodomain (TSHR-ECD) using molecular dynamics simulation Furthermore, analyzed their bioactivity in vitro using recombinant proteins to confirm that such binding was physiologically relevant. Examining the interaction of TSHβ and TSHβv with the TSHR-ECD model using molecular dynamic simulation revealed strong binding of these proteins to the receptor ECD. The specificity of TSHβ and TSHβv binding to the TSHR-ECD was examined by analyzing the hydrogen-bonding residues of these subunits to the FSH receptor ECD, indicating the inability of these molecules to bind to the FSH receptors. Furthermore, the modelling suggests that TSHβ and TSHβv proteins clasped the concave surface of the leucine rich region of the TSHR ECD in a similar way to the native TSH using dynamic hydrogen bonding. These mutually exclusive stable interactions between the subunits and ECD residues included some high-affinity contact sites corresponding to binding models of native TSH. Furthermore, we cloned TSHβ and TSHβv proteins using the entire coding ORF and purified the flag-tagged proteins. The expressed TSHβ subunit proteins retained bioactivity both in a coculture system as well as with immune-purified proteins. In summary, we showed that such interactions can result in a functional outcome and may exert physiological or pathophysiological effects in immune cells.

SAT-558 Tsh Modulation Of Bone Biology - Further Evidence From A Recombinant Tsh-β Variant

We have previously shown that TSH has modulatory influences on osteoblasts and osteoclasts and can act as a bone protection ligand. We have also shown that a novel TSH-β variant protein is produced locally by murine and human bone marrow macrophages (Endocrinology 154:4919-26, 2013 and Endocrinology 157:3658-67, 2016). Furthermore, we have also shown by molecular modelling that both TSH-β and TSH-βv can bind to the native TSH receptor. In order to characterize the biological activity of this TSH-β variant we have inserted the gene sequence together with a FLAG tag into the P-secTag2 vector which was then cloned into mammalian HEK-293 cells. Western blot analysis identified 17KD and a 12KD proteins corresponding to the wild type TSH-β and the TSH-βv nucleotide sequence in cell culture lysates and, less so in supernatants, by using a FLAG monoclonal antibody and a TSH-β polyclonal antibody. Protein bands of ~34 KD and 24 KD were observed only in the absence of DTT suggesting dimeric forms of TSH-β and TSH-βv respectively. Detection by Coomassie staining followed by sequence analysis using mass spectrometry confirmed the identity of these proteins after column purification. Furthermore, cyclic AMP responses were generated by both supernatant preparations with an 8-fold increase in luciferase activity with TSH-β and a 4-fold increase with TSH-βv. These data demonstrate the inherent bioactivity of single TSH-β chains which was mirrored by TSH-βv. Local paracrine action by macrophage derived TSH-βv on osteoblasts and osteoclasts is, therefore, most likely and raises the possibility of this variant form having significant osteoprotective activity.

Actions of pituitary hormones beyond traditional targets

Studies over the past decade have challenged the long-held belief that pituitary hormones have singular functions in regulating specific target tissues, including master hormone secretion. Our discovery of the action of thyroid-stimulating hormone (TSH) on bone provided the first glimpse into the non-traditional functions of pituitary hormones. Here we discuss evolving experimental and clinical evidence that growth hormone (GH), follicle-stimulating hormone (FSH), adrenocorticotrophic hormone (ACTH), prolactin, oxytocin and arginine vasopressin (AVP) regulate bone and other target tissues, such as fat. Notably, genetic and pharmacologic FSH suppression increases bone mass and reduces body fat, laying the framework for targeting the FSH axis for treating obesity and osteoporosis simultaneously with a single agent. Certain 'pituitary' hormones, such as TSH and oxytocin, are also expressed in bone cells, providing local paracrine and autocrine networks for the regulation of bone mass. Overall, the continuing identification of new roles for pituitary hormones in biology provides an entirely new layer of physiologic circuitry, while unmasking new therapeutic targets.

Expanding the Role of Thyroid-Stimulating Hormone in Skeletal Physiology

The dogma that thyroid-stimulating hormone (TSH) solely regulates the production of thyroid hormone from the thyroid gland has hampered research on its wider physiological roles. The action of pituitary TSH on the skeleton has now been well described; in particular, its action on osteoblasts and osteoclasts. It has also been recently discovered that the bone marrow microenvironment acts as an endocrine circuit with bone marrow-resident macrophages capable of producing a novel TSH-β subunit variant (TSH-βv), which may modulate skeletal physiology. Interestingly, the production of this TSH-βv is positively regulated by T3 accentuating such modulation in the presence of thyroid overactivity. Furthermore, a number of small molecule ligands acting as TSH agonists, which allosterically modulate the TSH receptor have been identified and may have similar modulatory influences on bone cells suggesting therapeutic potential. This review summarizes our current understanding of the role of TSH, TSH-β, TSH-βv, and small molecule agonists in bone physiology.

T3 Regulates a Human Macrophage-Derived TSH-β Splice Variant: Implications for Human Bone Biology

TSH and thyroid hormones (T3 and T4) are intimately involved in bone biology. We have previously reported the presence of a murine TSH-β splice variant (TSH-βv) expressed specifically in bone marrow-derived macrophages and that exerted an osteoprotective effect by inducing osteoblastogenesis. To extend this observation and its relevance to human bone biology, we set out to identify and characterize a TSH-β variant in human macrophages. Real-time PCR analyses using human TSH-β-specific primers identified a 364-bp product in macrophages, bone marrow, and peripheral blood mononuclear cells that was sequence verified and was homologous to a human TSH-βv previously reported. We then examined TSH-βv regulation using the THP-1 human monocyte cell line matured into macrophages. After 4 days, 46.1% of the THP-1 cells expressed the macrophage markers CD-14 and macrophage colony-stimulating factor and exhibited typical morphological characteristics of macrophages. Real-time PCR analyses of these cells treated in a dose-dependent manner with T3 showed a 14-fold induction of human TSH-βv mRNA and variant protein. Furthermore, these human TSH-βv-positive cells, induced by T3 exposure, had categorized into both M1 and M2 macrophage phenotypes as evidenced by the expression of macrophage colony-stimulating factor for M1 and CCL-22 for M2. These data indicate that in hyperthyroidism, bone marrow resident macrophages have the potential to exert enhanced osteoprotective effects by oversecreting human TSH-βv, which may exert its local osteoprotective role via osteoblast and osteoclast TSH receptors.

Thyroid and bone: macrophage-derived TSH-β splice variant increases murine osteoblastogenesis

It is now firmly established that TSH may influence the physiology and patho-physiology of bone by activating osteoblasts and inhibiting osteoclast activity resulting in relative osteoprotection. Whether this influence is directly exerted by pituitary-derived TSH in vivo is less certain, because we have previously reported that the suppression of pituitary TSH does not remove such protection. Here, we have characterized the functional relevance of a novel form of the TSH-β subunit, designated TSH-βv, known to be produced by murine bone marrow cells. We found that fresh bone marrow-derived macrophages (MØs) preferentially produced TSH-βv and, when cocultured with CHO cells engineered to overexpress the full-length TSH receptor, were able to generate the production of intracellular cAMP; a phenomenon not seen in control CHO cells, such results confirmed the bioactivity of the TSH variant. Furthermore, cocultures of MØs and osteoblasts were shown to enhance osteoblastogenesis, and this phenomenon was markedly reduced by antibody to TSH-β, suggesting direct interaction between MØs and osteoblasts as observed under the electron microscope. These data suggest a new paradigm of local modulation of bone biology by a MØ-derived TSH-like molecule and raise the question of the relative contribution of local vs pituitary-derived TSH in osteoprotection.

Hyperthyroid-associated osteoporosis is exacerbated by the loss of TSH signaling

The osteoporosis associated with human hyperthyroidism has traditionally been attributed to elevated thyroid hormone levels. There is evidence, however, that thyroid-stimulating hormone (TSH), which is low in most hyperthyroid states, directly affects the skeleton. Importantly, Tshr-knockout mice are osteopenic. In order to determine whether low TSH levels contribute to bone loss in hyperthyroidism, we compared the skeletal phenotypes of wild-type and Tshr-knockout mice that were rendered hyperthyroid. We found that hyperthyroid mice lacking TSHR had greater bone loss and resorption than hyperthyroid wild-type mice, thereby demonstrating that the absence of TSH signaling contributes to bone loss. Further, we identified a TSH-like factor that may confer osteoprotection. These studies suggest that therapeutic suppression of TSH to very low levels may contribute to bone loss in people.

The role of beta-endorphin in the acute motor stimulatory and rewarding actions of cocaine in mice

RATIONALE

Opioid receptor antagonists have been shown to attenuate the rewarding and addictive effects of cocaine. Furthermore, cocaine has been shown to cause the release of beta-endorphin, an endogenous opioid peptide.

OBJECTIVE

We assessed whether this neuropeptide would play a functional role in cocaine-induced motor stimulation and conditioned place preference (CPP).

MATERIALS AND METHODS

Mice lacking beta-endorphin and their wild-type littermates were habituated to motor activity chambers for 1 h, then injected with cocaine (0, 15, 30, or 60 mg/kg, intraperitoneally) or morphine (0, 5, or 10 mg/kg, subcutaneously), and motor activity was recorded for 1 h. In the CPP paradigm, mice were tested for baseline place preference on day 1. On days 2 and 3, mice received an alternate-day saline/cocaine (15, 30, or 60 mg/kg) or saline/morphine (10 mg/kg) conditioning session and then tested for postconditioning place preference on day 4.

RESULTS

Cocaine-induced motor stimulation and CPP were both reduced in mice lacking beta-endorphin. On the other hand, motor stimulation and CPP induced by morphine were not altered in mutant mice.

CONCLUSION

The present results demonstrate that the endogenous opioid peptide beta-endorphin plays a modulatory role in the motor stimulatory and rewarding actions of acute cocaine.

Bone loss in thyroid disease: role of low TSH and high thyroid hormone

More than 10% of postmenopausal women in the United States receive thyroid hormone replacement therapy and up to 20% of these women are over-replaced inducing subclinical hyperthyroidism. Because hyperthyroidism and post menopausal osteoporosis overlap in women of advancing age, it is urgent to understand the effect of thyroid hormone excess on bone. We can now provide results that not thyroid hormones but also TSH itself has an equally important role to play in bone remodeling.

High-mobility group box proteins modulate tumor necrosis factor-alpha expression in osteoclastogenesis via a novel deoxyribonucleic acid sequence

We have previously shown that mice lacking the TSH receptor (TSHR) exhibit osteoporosis due to enhanced osteoclast formation. The fact that this enhancement is not observed in double-null mice of TSHR and TNFalpha suggests that TNFalpha overexpression in osteoclast progenitors (macrophages) may be involved. It is unknown how TNFalpha expression is regulated in osteoclastogenesis. Here, we describe a receptor activator for nuclear factor-kappaB ligand (RANKL)-responsive sequence (CCG AGA CAG AGG TGT AGG GCC), spanning from -157 to -137 bp of the 5'-flanking region of the TNFalpha gene, which functions as a cis-acting regulatory element. We further show how RANKL treatment stimulates the high-mobility group box proteins (HMGB) HMGB1 and HMGB2 to bind the RANKL-responsive sequence and up-regulates TNFalpha transcription. Exogenous HMGB elicits the expression of cytokines, including TNFalpha, as well as osteoclast formation. Conversely, TSH inhibits the expression of HMGB and TNFalpha and the formation of osteoclasts. These results suggest that HMGB play a pivotal role in osteoclastogenesis. We also show a direct correlation between the expression of HMGB and TNFalpha and osteoclast formation in TSHR-null mice and TNFalpha-null mice. Taken together, we conclude that HMGB and TNFalpha play critical roles in the regulation of osteoclastogenesis and the remodeling of bone.

The mu opioid receptor is involved in buprenorphine-induced locomotor stimulation and conditioned place preference

The analgesic effect of buprenorphine is mediated via the mu opioid receptor (MOP). In the present study, using mice lacking the MOP and their wild-type littermates, we determined the role of the MOP in buprenorphine-induced locomotor stimulation and conditioned place preference (CPP). Buprenorphine (3 mg/kg) increased motor activity in wild-type but not in MOP knockout mice, showing the motor stimulatory action of buprenorphine is mediated via the MOP. When the mice were given the same treatment once daily for 5 consecutive days and challenged with buprenorphine on day 11, the motor stimulatory action of buprenorphine was enhanced in wild-type but not in MOP knockout mice, showing sensitization developed to the motor stimulatory action of buprenorphine and this phenomenon was mediated via the MOP. Likewise, buprenorphine induced CPP in wild-type mice after four alternate-day saline/buprenorphine (3 mg/kg) injections paired with olfactory and visual cues. However, buprenorphine failed to induce CPP in MOP knockout mice. In contrast, amphetamine (1 mg/kg) induced a comparable CPP in wild-type and MOP knockout mice. Together, the present results suggest that the ability of buprenorphine to increase motor activity and induce locomotor sensitization and CPP is mediated via the MOP.

Differential involvement of enkephalins in analgesic tolerance, locomotor sensitization, and conditioned place preference induced by morphine

In this study, the authors investigated the role of enkephalins in morphine-induced conditioned place preference, locomotor sensitization, and analgesic tolerance. Both preproenkephalin wild type (ppENK [+/+]) and knockout (ppENK [-/-]) mice showed similar preference for the morphine-paired chamber over the vehicle-paired chamber, indicating morphine induced comparable conditioned place preference in ppENK (+/+) and ppENK (-/-) mice. Sensitization developed to the motor stimulatory action of morphine after its repeated administration, but the magnitude of this response was not altered in ppENK (-/-) mice. However, as shown previously, ppENK (-/-) mice displayed blunted morphine analgesic tolerance. Taken together, the results suggest that enkephalins may be important for the development of analgesic tolerance but not for conditioned place preference or behavioral sensitization induced by morphine.