This same mechanism was also observed in paralyzed patients and volunteers who participated in a bed rest study. To uncover the molecular mechanism behind this protective process, the researchers collaborated with proteomics experts and identified nearly 2,700 proteins in the bears' platelets, shedding light on their unique ability to avoid thrombosis during hibernation.
HEAT SHOCK PROTEIN 47
A significant finding from the research project was the identification of 71 upregulated and 80 downregulated proteins during hibernation compared to summer activity in brown bears. One of the key proteins of interest was heat shock protein 47 (HSP47), which was downregulated by 55-fold in hibernating bears compared to their active state. This downregulation of HSP47 was also observed in other mammalian species, including humans and pigs, indicating a conservation mechanism for thrombosis prevention during immobilisation.
The researchers further demonstrated that reducing HSP47 protein levels led to decreased interaction between blood platelets and inflammatory cells. HSP47 was found to be capable of directly activating inflammatory cells, which could potentially increase the risk of venous thrombosis in immobilized acute patients. Therefore, blocking HSP47 with suitable molecules could be a potential strategy to prevent thrombosis in such patients. While currently available small molecules for HSP47 inhibition are not suitable for human use, the researchers plan to search for suitable substances to explore new treatment possibilities for individuals at risk of thrombosis.
Molecular chaperones are proteins that help fold newly synthesized polypeptides into their proper 3D structure or keep them inactive until they reach their correct location in the cell. They are also called heat shock proteins (HSPs) because they increase in cells under stress. These chaperones are found in many cell types and play essential roles in maintaining protein folding, cellular organization, and complex assembly. Some Hsps also have cytoprotective functions during stress. Others, like αB-crystallin in the eye and heart, or Hsp47 in collagen-producing cells, have specialized roles. They help with specific protein assembly or stability, and their levels may change in disease conditions.
HSP47 is another example of a specialized HSP. It is selectively expressed in the endoplasmic reticulum of cells that synthesize and secrete type I or type III collagen under normal conditions. HSP47 physically associates with procollagen molecules, stabilizes procollagen monomers, prevents premature aggregation, and modulates their transfer to the Golgi apparatus for export from the cell. Increased levels of Hsp47 and type I collagen are observed in tissues undergoing pathological fibrosis, and inhibiting Hsp47 expression decreases type I collagen production.