Skerry, T. M. | bioRxiv Science

bioRxiv2024

Receptor activity modifying protein modulation of parathyroid hormone-1 receptor function and signalling.

Receptor activity-modifying proteins (RAMPs) are known to modulate the pharmacology and function of several G protein-coupled receptors (GPCRs), including the parathyroid hormone 1 receptor (PTH1R). However, the precise effects of different RAMPs on PTH1R signalling and trafficking remain poorly understood. Here we investigated the impact of RAMP2 and RAMP3 on PTH1R function using a range of PTHand PTH-related protein (PTHrP)-derived ligands. FRET imaging revealed that PTH1R preferentially interacts with RAMP2 and, to a lesser extent, RAMP3, but not RAMP1. Interestingly, RAMP3 co-expression resulted in reduced cell surface expression of PTH1R, suggesting a potential role in receptor trafficking or internalization. The presence of RAMP2 significantly enhanced PTH1R-mediated cAMP accumulation, {beta}-arrestin recruitment, and calcium signalling in response to PTH (1-34), PTHrP (1-34), PTH (1-84), and the PTH (1-17) analogue ZP2307. In contrast, RAMP3 co-expression attenuated or completely abolished those responses. We found that full-length PTHrP analogues, PTHrP (1-108) and PTHrP (1-141), exhibited lower potency and efficacy than PTHrP (1-34) in activating PTH1R. RAMP2 significantly increased potency and/or efficacy when compared to PTH1R alone cells, while RAMP3 significantly reduced these responses. Antibody-capture scintillation proximity assays demonstrated that RAMP2 differentially modulates G protein activation by PTH1R in a ligand-dependent manner, with PTH (1-34) and PTHrP (1-34) inducing distinct patterns of G protein subtype activation. These findings highlight the complex role of RAMPs in regulating PTH1R signalling and trafficking, revealing differential effects of RAMP2 and RAMP3 on receptor function. The data suggest that targeting the PTH1R/RAMP2 complex may be a promising strategy for developing novel bone anabolic therapies by leveraging biased agonism and functional selectivity. Further research using physiologically relevant models is needed to elucidate the therapeutic potential of this approach.

pharmacology and toxicology↗

bioRxiv2020

Feeding intervention potentiates the effect of mechanical loading to induce new bone formation in mice

The benefits of increased human lifespan depend upon duration of healthy, independent living; the healthspan. Bone-wasting disorders contribute significantly to loss of independence, frailty and morbidity in older people. Therefore, there is an unmet need globally for lifestyle interventions to reduce the likelihood of bone fractures with age. Although many mechanisms are involved in disorders of bone loss, there is no single regulatory pathway and, therefore, there is no single treatment available to prevent their occurrence. Our aim in these studies was to determine whether fasting/feeding interventions alter the effect of mechanical loading on bone anabolic activities and increase bone mass. In young 17-week-old mice, 16-hour fasting period followed by reintroduction of food for 2 hours increased markedly the potency of mechanical loading, that mimics the effect of exercise, to induce new cortical bone formation. Consistent with this finding, fasting and re-feeding increased the response of bone to a loading stimulus that, alone, does not stimulate new bone formation in ad-lib fed mice. Older mice (20-months) experienced no potentiation of loading-induced bone formation with the same timing of feeding interventions. Interestingly, the pre-, prandial and postprandial endocrine responses in older mice were different from those in young animals. The hormones that change in response to timing of feeding have osteogenic effects that interact with loading-mediated effects. Our findings indicate associations between timing of food ingestion and bone adaptation to loading. If translated to humans, such non-pharmacological lifestyle interventions may benefit skeletal health of humans throughout life-course and in older age.

physiology↗