An Explanation of Bone Remodeling Involving the Rejuvenating Protein DEL-1

(The eye-catching image is cited from a free Getty Images photo of bone cells)

In the previous article, I introduced the rejuvenating protein known as DEL-1. (This article is written so that it can be understood even if you haven't read the previous one.)

There are research reports indicating that DEL-1 is particularly effective for anti-aging of bones within cells.

Human bones do not remain in the same state forever once they are formed.
Old bone is broken down, and new bone is created. This mechanism is called "
bone remodeling."

The cells that break down old bone are "osteoclasts." The cells that create new bone are "
osteoblasts." The cells trapped inside the bone that monitor it are "
osteocytes." Note that in terms related to bone remodeling, the character for bone is read as "kotsu" in all cases, such as "hakotsu" and "kotsuga," rather than "hone."kotsu
.

When you are young, the balance between the work of breaking down bone and creating bone is maintained. However, due to
aging, this balance is prone to collapse. When the
speed of creating new bone cannot keep up with the speed of breaking down bone, the bones gradually become weaker.

DEL-1 is involved in this bone remodeling. This is because DEL-1 is thought to assist in three functions: processing old cells, suppressing inflammation, and creating new cells.

In this article, I will explain bone remodeling involving DEL-1. (Research on bone anti-aging by DEL-1 will be introduced in the next article.)

1. Bones are constantly being rebuilt throughout life

Many people may think that "human bones are just left to age once they are formed." However, actual bone is a
living tissue that breaks down old bone and creates new bone in its place, repeating this process throughout one's life. This
metabolism, which combines the "breaking down" and "creating" of bone, is bone remodeling.

Bones are like pillars that support the body.
However, their contents are not inorganic materials like concrete.
Inside the bone, many cells continue to work.
Cells that break down old bone, cells that create new bone, cells that monitor the state of the bone, and others communicate with each other to adjust the condition of the bone.

Bone remodeling is very similar to renovating a house by tearing down old parts and repairing them with new materials.
However, there is a major difference from home renovation.
In the case of bone, this work is happening all over the body and continuously in parallel.
Therefore, the entire bone is not destroyed and renewed all at once.

Small areas of old bone are removed and new bone is created in their place, a process that is throughout the body and constantly repeated.
In adult bone, it is estimated that about 5% per year is replaced through remodeling, and by simple calculation, it would correspond to 20 years for the entire skeleton to be renewed.
On the other hand, general explanations sometimes state that "about 10 years" is required for bone replacement.
However, this does not mean that "all the bone in the body becomes brand new after 10 to 20 years."
This is because the speed varies depending on the type of bone, location, age, hormonal status, etc.

An important fact is that "bone continues to change throughout life."
In other words, the current bone is not the same bone that was made when you were a child.
It is repaired little by little in daily life and replaced with new bone.

2. Three types of cells responsible for bone remodeling

There are three types of cells responsible for bone remodeling.

① Osteoclasts ② Osteoblasts ③ Osteocytes

① Osteoclasts: Break down old bone

Osteoclasts are cells that break down old bone.

On the surfaceof the bone, it creates a small sealed space between itself and the bone. Then, it pumps
acid into that area to dissolve minerals such as calcium and phosphorus that support the hardness of the bone. Furthermore, it releases
enzymes that break down collagen, which is one of the main components of bone.

In this way, old bone is gradually removed. In other words, osteoclasts are not
bad cells that weaken bone. Rather, they are
essential for removing old or damaged bone and replacing it with new bone. In terms of home renovation, they play a role similar to a demolition contractor
that removes old walls and floors. In bone remodeling, this destruction work happens first.

② Osteoblasts: Building new bone

Working after osteoclasts have removed old bone are osteoblasts.

Osteoblasts build new bone in the areas that were carved out. What they
build first is not immediately hard bone. They create the
foundation material for bone, known as bone matrix. The core of this bone matrix is
collagen. As
minerals such as calcium and phosphorus deposit onto the foundation created by collagen, it gradually turns into hard bone.

In terms of home renovation, osteoblasts are the construction crew that uses new materials to build the structure.

③ Osteocytes: Monitoring the state of the bone

And another important component is osteocytes.

When osteoblasts create new bone, some of them become trapped within the bone they have created.
Then, the osteoblasts transform into osteocytes.
Although osteocytes are embedded within the bone, they are by no means dormant.
They extend slender projections inside the bone to form a network with surrounding osteocytes and other cells.
Through this network, they sense the forces and changes applied to the bone.
In other words, osteocytes are like sensors installed inside the bone.
They play an important role in sensing how much force is being applied to the bone and where the load is concentrated, and in regulating bone remodeling.

Bone is not simply a matter of "destroying cells" and "creating cells" working.
Osteocytes monitor the state of the bone and, based on that information, the activities of osteoclasts and osteoblasts are regulated.

3. Bone remodeling proceeds through "destroying → cleaning → creating"

Bone remodeling is not just a case of "osteoclasts work, then osteoblasts work."
In reality, it proceeds through five stages.

① Initiation ② Bone resorption ③ Reversal ④ Bone formation ⑤ Quiescence

① Initiation: Deciding where to repair

Bone remodeling does not begin indiscriminately anywhere in the bone.

When force is repeatedly applied to bone in daily life, micro-damage (microcracks) or changes can occur.
When osteocytes sense these phenomena, information regarding the location where bone repair is needed is transmitted.

Then, bone remodeling is initiated at that location.
The osteocytes are essentially signaling, "This location needs to be repaired."

② Bone resorption: Osteoclasts destroy old bone

Next, osteoclasts gather at the site targeted for repair.
Osteoclasts adhere closely to the bone surface, and use acid and enzymes to remove old bone.
They dissolve calcium and phosphorus as minerals, and also break down organic components such as collagen
. In this way, the old bone is removed.

This process is called bone resorption.
Resorption here does not mean absorbing nutrients from the intestines.
It is used to mean that bone tissue is broken down by cells and returned to the body.

③ Reversal: Switching from "breaking down" to "building"

Once bone resorption is complete, the process enters a stage called reversal.
This is a very important part of bone remodeling because it is where the process switches from "breaking down bone" to "building bone."

In the areas scraped away by osteoclasts, debris from the broken-down bone remains.
Cells that prepare the surface work there to create an environment where the next bone-building cells can function.
At the same time, it is thought that substances released from inside the bone due to bone resorption and signals emitted from osteoclasts and others promote bone formation by osteoblasts.

In other words, the "breaking down" and "building" of bone are not completely independent.
There is a mechanism called coupling where the initial bone resorption leads to subsequent bone formation.

④ Bone formation: Osteoblasts build new bone

Next, osteoblasts appear.
Osteoblasts gather at the sites scraped by osteoclasts and first create bone matrix, which is the foundation of new bone centered on collagen.
After that, calcium and phosphorus are deposited onto that foundation, and it gradually turns into hard bone.

This work of building new bone is called bone formation.
Bone formation takes longer than bone resorption.
In other words, bone remodeling does not proceed at the same speed for "breaking down" and "building."
Therefore, it is important that the amount of bone broken down and the amount built balance out accurately.

⑤ Quiescence: New bone is completed and waits for the next repair

Once enough new bone has been built, the area returns to a stable state.
Then, after a while, new bone remodeling begins in another location.
In this way, small repair projects of "breaking down and building" are being carried out in parallel in bones all over the body.

The above process is the "mechanism by which bone is maintained throughout one's entire life."

4. The reason why bone is deliberately "broken down and then built"

Some people might think, "If the bone is old, shouldn't we just reinforce it without breaking it down?"
Actually, bone remodeling has a very important significance.

① Repairing small cracks in the bone

In daily life, people repeatedly place stress on their bones through activities like walking, running, and carrying objects.
As a result, invisible, tiny damages can occur inside the bones.
These are called micro-damage or microcracks.
Even if each one is a small injury, if they accumulate over a long period, they may affect the strength of the bone.

Therefore, through bone remodeling, damaged parts are removed and replaced with new bone.
In other words, bone remodeling can be thought of as regular maintenance for bones.

② Replacing old bone with new bone

Bones are not necessarily strong just because they are hard.
Bones require both hardness and flexibility.

If old bone remains for a long time, the properties of the bone change, which can be disadvantageous for maintaining bone quality.
Bone remodeling maintains the condition of the bone by replacing old parts with new bone.

③ Regulating calcium concentration in the blood

Bones have another extremely important role: calcium storage.
Most of the calcium in the body is stored in the bones and teeth, and bones act like a giant warehouse for storing calcium.

Calcium is not just a substance needed to build bones.
It is an essential mineral for vital activities such as muscle contraction, nerve function, and blood coagulation
.Therefore, the calcium concentration in the blood must be kept within a narrow range.

When calcium in the blood is insufficient, calcium is mobilized from the bones through regulation by hormones and other factors.
Conversely, if calcium is sufficiently supplied, it is stored again in the bones through bone formation.

5. When the balance of bone remodeling is disrupted, it leads to osteoporosis

In healthy young adults, the "amount destroyed" and the "amount created" are basically balanced.
Even if osteoclasts remove old bone, if osteoblasts create roughly the same amount of bone, the total amount of bone does not change significantly.
This can be considered a state where the balance of bone remodeling is maintained.

However, this balance deteriorates with aging.
Especially from middle age onwards, the amount of new bone being formed may not sufficiently keep up with the amount of bone being broken down.
As a result, the total amount of bone decreases little by little.

When this condition progresses, it leads to osteoporosis.
It is important to note that osteoporosis is not simply a disease caused by a lack of calcium.
The balance between the work of breaking down bone and the work of building bone is disrupted, and it is important that not only the bone mass but also the internal structure and quality of the bone change.

Bone aging is related to various factors.
Among them, what is particularly important for women is estrogen.
Estrogen is a type of female hormone, but it also has an important role in bone.
Estrogen has the function of suppressing bone resorption by osteoclasts.
However, when menopause is reached, estrogen secretion decreases significantly.
As a result, bone resorption by osteoclasts becomes active, leading to a high-turnover state where bone turnover itself accelerates.
If bone formation cannot keep up with the speed of bone resorption, the result is that bone is gradually lost.

In other words, osteoporosis is not a phenomenon where bones suddenly become weak because you have aged.
It appears as a result of the difference between "breaking down" and "building up" accumulating little by little over many years.

Summary: Bones "can maintain their strength precisely because they are being broken down"

Bone remodeling is a lifelong maintenance system for bones that removes old bone and replaces it with new bone.

The core of this process involves osteoclasts—osteoblasts—osteocytes. Osteoclasts
break down old bone, osteoblasts create new bone, and osteocytes senseforces applied to the bone to regulate bone remodeling.

Bone remodeling proceeds through the sequence of activation → resorption → reversal → formation → quiescence. It is precisely because this balance is maintained that bones can
repair minor damage caused by daily stress and maintain their strength.

Bones have another extremely important role: calcium storage. However, when the
balance between bone resorption and bone formation is disrupted due to aging or decreased estrogen following menopause, bone mass can gradually decrease. This is a key mechanism that leads to
osteoporosis.

In other words, when considering bone health, what is truly important is not just "not breaking down bone."
It is about maintaining the overall balance of bone remodeling, which is to properly break down old bone and correctly build new bone.

Bone is not a tissue that, once created, remains unchanged for life.
As long as a person is alive, repeated cycles of demolition and construction are occurring within the bones.
This repetition supports the human body, allows for movement, and protects vital activities.

This time, I will link to information about collagen.
There was a time when it was said that even if collagen is ingested orally, it is broken down into amino acids and does not reach the bones.
However, the recent view is that it does reach the bones because it is not all broken down into amino acids, but also exists in the form of collagen peptides.

Additionally, I personally believe it is better not to take calcium supplements.
Taking them can lead to a phenomenon called the calcium paradox, where calcium actually leaches out of the bones.

This article is intended to provide general health information and is not intended for the diagnosis, treatment, or prevention of any specific disease.
If you have any concerns about your physical condition, please consult a professional such as a doctor.

The next post will be published on Thursday, August 6th, at 10:00 AM. The world's top-level research institution for DEL-1 research is
Niigata University. I will explain the
Niigata University research announced in 2026.

Thank you for reading until the end.
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