Japanese researchers have discovered an overlap between the mechanism of hair color determination and bone resorption.
- Bone is resorbed by osteoclasts, which rely on a group of small “Rab” proteins regulating logistics between various compartments within cells.
- Proteins called Rab32 and Rab38 play a central role in bone resorption in osteoclasts.
- These proteins are also crucial for hair and skin pigmentation.
If there is an imbalance between bone formation and resorption, diseases such as osteoporosis, rheumatism and periodontitis can occur. As a reminder, bones are resorbed by a cell, called an “osteoclast,” and several substances, such as acids and enzymes, are secreted in the places where the osteoclast attaches to the bones and where resorption occurs. Osteoclasts depend on a group of small proteins, called “Rab”, which regulate logistics between various compartments within cells.
Rab32 and Rab38 proteins are crucial for bone resorption and hair pigmentation
However, “the Rab proteins involved have been little understood. To better understand the molecular mechanisms of osteoclast function, we first examined the Rab proteins particularly induced during osteoclast formation in mice”, said Kazuya Noda, professor at Osaka University (Japan). As part of’a first study, the scientist and her team discovered that the Rab32 and Rab38 proteins played a central role in bone resorption in osteoclasts. They are both crucial in determining hair color, regulating logistics to the melanosome, an organelle specialized in pigmentation of skin and hair-forming cells.
In a second study, the researchers conducted an experiment on a mouse lacking Rab32 and Rab38 proteins. Result: the animal had beige hair color and red eyes, while the wild-type mouse has black hair and eyes. The authors found that the rodent lacking both proteins had increased bone density and that with age, its spine became more deformed. “We also showed that bone resorption by osteoclasts is defective in mice whose proteins are doubly inactivated,” explained Shiou-ling, co-author of the work.
Understanding the mechanism of bone resorption to better treat bone diseases
As a reminder, bone diseases such as osteoporosis, rheumatism and periodontitis are associated with hyperactivation of bone resorption by osteoclasts. “Therefore, understanding the underlying mechanism of bone resorption facilitated by Rab32 and Rab38 will provide us with useful information regarding potential therapeutic targets for these pathologies,” concluded Takeshi Noda, who participated in both researches.