Pre-proenkephalin 1 is Downregulated Under Unloading and is Involved in Osteoblast Biology

Area of Science:

• Bone Biology
• Mechanobiology
• Neuropeptide Signaling

Background:

• Pre-proenkephalin 1 (Penk1) is an opioid peptide with analgesic properties.
• Penk1 is downregulated in osteoblasts under mechanical unloading (microgravity model).
• Penk1 downregulation is observed in vivo (tail-suspension, botox injection) and in humans during bed rest.

Purpose of the Study:

• To investigate the role of Penk1 in bone metabolism and response to mechanical unloading.
• To determine the effect of Penk1 deletion on osteoblast differentiation and activity.

Main Methods:

• In vivo models of mechanical unloading (tail-suspension, botox injection) in mice.
• Analysis of Penk1 expression in sera from healthy volunteers during bed rest.
• In vitro studies using osteoblasts, including Penk1 gene silencing (siRNA) and treatment with Met-enkephalin.
• Assessment of osteoblast differentiation, activity, mineralization, and Wnt pathway signaling.
• Phenotypic analysis of Penk1 knockout (Penk1-/-) mice.

Main Results:

• Penk1 global deletion in mice did not result in an overt bone phenotype.
• In vitro, Penk1 gene expression increased during osteoblast differentiation.
• Transient Penk1 silencing in mature osteoblasts altered Wnt pathway signaling (increased SOST1, decreased WNT3A, COL1A1).
• Met-enkephalin treatment enhanced osteoblast differentiation markers (OSX, COL1A1) and mineralization.
• Primary osteoblasts from Penk1-/- mice exhibited reduced metabolic activity, ALP activity, mineralization, and colony formation.

Conclusions:

• Penk1 plays a role in regulating bone's response to mechanical unloading.
• Penk1 influences osteoblast differentiation and activity in a cell-autonomous manner.
• These findings suggest Penk1 as a potential target for managing bone loss associated with unloading.