Dimeric R25CPTH(1-34) Peptide Activates the Parathyroid Hormone-1 Receptor and Stimulates Bone Formation in Osteoporotic Mice

Główne pojęcia

A dimeric form of the R25CPTH(1-34) peptide, a variant of parathyroid hormone, can activate the PTH1 receptor and stimulate bone formation in osteoporotic mouse models, suggesting its potential as a novel therapeutic for osteoporosis.

Streszczenie

This study investigates the functional properties of a dimeric form of the R25CPTH(1-34) peptide, a variant of parathyroid hormone (PTH) with a cysteine substitution at position 25. The key findings are:

The R25CPTH(1-84) peptide can form dimers both intracellularly and extracellularly due to the introduced cysteine residue.

The dimeric R25CPTH(1-34) peptide exhibits altered activity on the PTH1 receptor (PTH1R) compared to the monomeric form, with moderate selectivity for the G protein-coupled RG conformation of the receptor.

A single injection of dimeric R25CPTH(1-34) in mice induced acute calcemic and phosphaturic responses comparable to PTH(1-34).

Repeated daily injections of dimeric R25CPTH(1-34) in intact mice increased calvarial bone thickness and improved trabecular and cortical bone parameters in ovariectomized osteoporotic mice, similar to the effects of PTH(1-34).

Unlike PTH(1-34), dimeric R25CPTH(1-34) did not significantly increase plasma cAMP levels in mice, suggesting differences in the activation of downstream signaling pathways.

Overall, the results reveal the surprising capacity of a dimeric PTH peptide ligand to activate the PTH1R and stimulate bone formation, suggesting a potential new approach for developing therapeutic PTH analogs for osteoporosis.

Statystyki

Dimeric R25CPTH(1-34) induced acute increases in blood ionized calcium levels in mice that were comparable to those induced by PTH(1-34).
Dimeric R25CPTH(1-34) injection in mice led to a slight decrease in plasma phosphate levels at 2 hours post-injection, while PTH(1-34) induced a significant decrease at 1 hour.
Injection of dimeric R25CPTH(1-34) significantly increased urine phosphate levels at 2 hours post-injection in mice.
Treatment with dimeric R25CPTH(1-34) in ovariectomized osteoporotic mice increased femoral cortical bone mineral density by 104%, cortical bone volume fraction by 125%, cortical thickness by 107%, and cortical area fraction by 116%.
Serum levels of bone formation markers P1NP and alkaline phosphatase were significantly increased in both PTH(1-34) and dimeric R25CPTH(1-34) treated groups in ovariectomized mice.

Cytaty

"The overall results reveal a surprising capacity of a dimeric PTH peptide ligand to activate the PTH1R in vitro and in vivo, suggesting a potential new path of therapeutic PTH analog development."
"Considering the proven bone-anabolic capacity of several established PTH agonist ligands, and the need for safe, long-term treatments for skeletal disorders, our studies on dimeric R25CPTH(1–34) suggest alternative strategies to consider in such drug development programs."

Kluczowe wnioski z

Dimeric R25CPTH(1–34) Activates the Parathyroid Hormone-1 Receptor in vitro and Stimulates Bone Formation in Osteoporotic Female Mice

by Noh,M., Che,... o www.biorxiv.org 03-14-2024

https://www.biorxiv.org/content/10.1101/2024.03.13.584815v1

Głębsze pytania

What are the potential mechanisms underlying the differences in signaling and biological responses between monomeric and dimeric forms of the R25CPTH peptide?

The differences in signaling and biological responses between the monomeric and dimeric forms of the R25CPTH peptide can be attributed to several potential mechanisms. Firstly, the dimeric structure of R25CPTH may alter the binding mode to the PTH1R, leading to changes in receptor conformation and downstream signaling pathways. The dimeric form may have different affinities for the RG and R0 receptor conformations, impacting the activation of intracellular signaling cascades such as the cAMP-PKA pathway. This altered binding affinity and selectivity can result in differential activation of downstream effectors, influencing the overall biological response.
Additionally, the stability and pharmacokinetics of the dimeric peptide may differ from the monomeric form, affecting its bioavailability and duration of action. The dimeric R25CPTH peptide may have distinct interactions with receptor complexes, leading to unique cellular responses and functional outcomes. Furthermore, the dimeric structure could modulate interactions with other proteins or receptors, influencing the overall signaling network and biological effects of the peptide.

How might the dimeric R25CPTH peptide be further optimized or modified to enhance its bone anabolic effects and minimize potential side effects compared to existing PTH-based therapies?

To enhance the bone anabolic effects and minimize potential side effects of the dimeric R25CPTH peptide, several optimization strategies can be considered. Firstly, structural modifications can be explored to fine-tune the dimeric peptide's binding affinity and selectivity for the PTH1R, optimizing its interaction with the receptor and downstream signaling pathways. Rational design approaches, such as site-directed mutagenesis or peptide engineering, can be employed to enhance the peptide's potency and specificity towards bone-forming pathways.
Moreover, targeted delivery systems or formulations can be developed to improve the pharmacokinetic profile and tissue-specific accumulation of the dimeric peptide, enhancing its efficacy while reducing off-target effects. Utilizing nanotechnology or conjugation strategies, the dimeric R25CPTH peptide can be encapsulated or targeted to bone tissues, maximizing its bone anabolic effects while minimizing systemic exposure and potential adverse reactions.
Furthermore, combination therapies or synergistic approaches can be explored to enhance the overall bone-building effects of the dimeric peptide. By combining the dimeric R25CPTH with other bone-targeting agents or growth factors, synergistic effects on bone formation and remodeling can be achieved, providing a comprehensive and potent treatment strategy for osteoporosis.

Given the connection between the R25CPTH mutation and high bone mineral density observed in a patient, what insights could further study of this natural variant provide for understanding PTH receptor activation and bone metabolism regulation?

Further study of the R25CPTH mutation and its association with high bone mineral density in a patient can provide valuable insights into PTH receptor activation and bone metabolism regulation. By elucidating the molecular mechanisms underlying the enhanced bone-building effects of the R25CPTH variant, researchers can gain a deeper understanding of the structural determinants and functional consequences of PTH receptor activation.
Investigating the impact of the R25CPTH mutation on PTH1R signaling pathways, downstream effectors, and bone remodeling processes can reveal novel insights into the complex interplay between PTH, its analogs, and bone metabolism. Understanding how the dimeric R25CPTH peptide modulates osteoblast and osteoclast activity, bone formation, and resorption can shed light on potential therapeutic targets for osteoporosis and other bone-related disorders.
Moreover, studying the natural variant can provide a unique perspective on the physiological role of PTH and its analogs in maintaining bone health and mineral homeostasis. By characterizing the effects of the R25CPTH mutation in preclinical models and clinical studies, researchers can uncover new avenues for drug development, personalized medicine approaches, and targeted therapies for bone disorders.