Effect of calcium ions on human calcitonin. Possible implications for bone resorption by osteoclasts

Abstract

Calcium ions (Ca(2+)) are indispensable for life and are involved in important physiological actions, which makes maintaining a constant level of blood Ca(2+) essential. Ca(2+) is mainly stored in bones which serve as a reservoir and its homeostasis is modulated by various hormones. Human calcitonin (hCt) is a small peptide hormone that exerts its physiological effect on Ca(2+) metabolism by means of osteoclast-mediated bone resorption inhibition. Most of these actions are mediated through peptide/receptor interaction that acts via a second messenger. However, in vitro studies have shown that hCt can interact with membrane lipids to form ion channels in membrane models. This ability is due to the peptide's secondary structure and aggregation state, that can be modulated by different molecules. In our study, we evaluated the effect of Ca(2+), at different concentrations, both on the hCt ion channel incorporated into a planar lipid membrane made up of phosphatidylcholine containing 15% phosphatidylglycerol and on the secondary structure of hCt in an aqueous environment. Ca(2+) is able to interact with the hCt peptide by acting on the channel incorporated into the membrane as well as on the peptide in solution, both by increasing hCt channel frequency and in solution promoting α-helix formation, that counteracts the fibrillating process. These experimental observations, suggesting that hCt senses Ca(2+) concentration variations, strengthen the hypothesis that channel formation represents an extra source of Ca(2+) entry into osteoclasts in addition to the well-known interaction of the monomer with the specific receptor.

Structural Biology of Calcitonin: From Aqueous Therapeutic Properties to Amyloid Aggregation

“…Despite the prevalence of these larger species of prefibrillar aggregates, smaller (<20mer) prefibrillar oligomers are the species putatively responsible for membrane permeabilization, exhibiting enhanced pore‐formation activity ,,,. As with several other amyloid peptides, pore formation by CT oligomers leads to calcium leakage and loss of cell homeostasis, with this behavior being modified by both membrane composition and membrane structure ,,,,. As mentioned previously, the biological relevance of such pore formation remains unknown.…”

“…CT‐membrane interactions have been studied extensively, both for the possibility of physiological relevance via pore formation, and for the increasing prevalence of lipid‐based delivery options for therapies ,,,. As with other amyloid peptides, CT preferentially interacts with membranes containing anionic lipids, cholesterol, and GM1 ganglioside ,,,,,,.…”

“…Loss of focal adhesions leads to decreased efficiency in resorption and eventual decline in overall osteoclast numbers . CT can also form calcium permeable pores in lipid bilayers, with some claiming that such ion flow could lead to osteoclast detachment from the bone matrix ,,,. A role for calcium permeable CT pores in vivo requires further exploration, although calcium‐dependent alterations of osteoclast function are known ,…”

Glucagon‐like peptide 2 decreases osteoclasts by stimulating apoptosis dependent on nitric oxide synthase

“…And TRAP produced by osteoclasts can alleviate the inhibitory effect of OPN on mineralization, suggesting a potential role for TRAP in skeletal mineralization . Furthermore, human calcitonin (hCt) is a small peptide hormone that exerts its physiological effect on Ca(2 + ) metabolism by means of osteoclast‐mediated bone resorption inhibition …”

“…24 Furthermore, human calcitonin (hCt) is a small peptide hormone that exerts its physiological effect on Ca(2 + ) metabolism by means of osteoclastmediated bone resorption inhibition. 25 Furthermore, it is obvious that GLP2 activates the TGFβ-Smad2/3 signalling. Herein, the involvement of GLP2 is supported by results from 5 parallel sets of experiments: (i) GLP2 enhances the interaction between TGFβRII and SARA, and between TGFβRII and regulates RANKL-induced osteoclastogenesis through reciprocal cooperation between Smad2/3 and c-Fos.…”