For anyone who has ever studied the science of how the molecular biology of the growth plate within hormones interact this post will be a complete outline and summary on one of the best well understood hormone/protein pathways. It includes the Parathyroid Hormone-Related Protein (PTHrP), Parathyroid Hormone (PTH), and Indian Hedgehog (Ihh).

Because it is so well understood, it is easy to understand why and how it affects the fate of the growth plates.

Analysis & Interpretation

If you treated young mice (not adult mice) with the PTH, growth plate thickness, chondrocyte number, and the overall bone lengthen increases. If you tried to unload the bone, you decrease all three. If you did PTH administration with unloading, the PTH reduces the effect of unloading the bone.

The PTHrP (parathyroid hormone related peptide) and Ihh (indian hedgehog) works in a growth restraining feedback loop by controlling the pace of chondrocyte differentiation in the human growth plate. The PTHrP and Ihh are expressed at the same chondrocytes are the estrogen receptors alpha and beta types. If you remove either the PTH or the PTHrP it results in bone abnormal growth which is usually stunting from the chondrocytes which age faster and multiply slower.

IHH, PTHrP, and PTH/PTHrP receptor mRNA were detected in prehypertrophic and hypertrophic chondrocytes in both sexes during development. The presence of IHH, PTC, PTHrP, and PTH/PTHrP receptor protein in prehypertrophic and hypertrophic chondrocytes. In addition, staining for hedgehog, PTC, and PTHrP also was observed in growth plate stem cells. Furthermore, no mRNA or protein expression of the mentioned factors was detected in the perichondrium. Our data suggest that in contrast to the proposed feedback loop in the early embryonic growth plate, which requires the presence of the perichondrium, a feedback loop in the postnatal growth plate can be confined to the growth plate itself. In fact, two loops might exist: (1) a loop confined to the transition zone and early hypertrophic chondrocytes, which might in part be autocrine and (2) a loop involving the growth plate stem cells.

Indian hedgehog (IHH), produced by prehypertrophic and hypertrophic chondrocytes, stimulates production of parathyroid hormone-related protein (PTHrP) by perichondrial and early chondrocytic cells. PTHrP then maintains chondrocytes in a proliferative, less differentiated state. IHH and PTHrP may participate in a negative feedback loop that synchronizes and determines the pace of differentiation of chondrocytes in the growth plate. IHH is a master regulator of both chondrocyte and osteoblast differentiation.

PTHrP appears to act as a bifunctional modulator of both chondrocyte proliferation and differentiation, through signal transduction linked to the PTH/PTHrP receptor and by its direct action in the nucleolus. While the downstream promoter controls PTH/PTHrP receptor gene expression in bone and cartilage, it is differentially regulated in the two tissues. 1alpha,25-dihydroxyvitamin D3 downregulated the activity of the downstream promoter in osteoblasts, but not in chondrocytes, both in vivo and in vitro

As always the most important parts are highlighted.

From PubMed study HERE

PTHrP and the regulation of longitudinal growth: Exploring novel strategies to increase final height in children with short stature.

Dit is de samenvatting van de aanvraag.

Longitudinal growth is controlled by the activity of the chondrocytes in the epiphyseal plate, which is present at the distal ends of the long bones, and is regulated by a multitude of hormones, growth factors and metabolic conditions. Among these, gonadal steroids and particularly estrogen, are of pivotal importance. In humans, estrogen is responsible for growth plate closure causing a complete arrest in longitudinal growth at the end of puberty. The molecular mechanisms by which estrogen influences longitudinal growth and induces growth plate closure are largely unknown. One such mechanism can be the growth restraining feedback loop consisting of Parathyrooid Hormone related Peptide (PTHrP) and Indian Hedgehog (Ihh). This feedback loop has been shown to regulate longitudinal bone growth by controlling the pace of chondrocyte differentiation in the embryonal chicken, mice and human growth plate. More recently, we have shown that this feedback loop is also operational after birth. In addition, we have found that PTHrP, Ihh and estrogen receptors Era and ß are co-expressed in the same growth plate chondrocytes and that gonadectomy influences the expression of components of the feedback loop. A role for PTHrP in growth plate closure is furthermore supported by observations in humans and transgenic mice, in which the presence of an constitutively activating mutation in the PTH/PTHrP-receptor results in dwarfism and premature growth plate closure. At present, the molecular mechanisms by which the PTHrP/Ihh-feedback loop controls chondrocyte differentiation and is modulated by estrogen are largely unknown. The aims of the present project are: To gain more insight in the molecular mechanism by which ethe PTHrP/Ihh feedback loop controls the pace of chondrocyte differntiation with empasis on the identification of PTHrP target genes and interactions with members of the TGFß/BMP-superfamily. To characterize the interactions between the PTHrP/Ihh-feedback loop and estrogen and to determine its role in growth plate closure. To examine the relevance of the findings in experimental models for longitudinal growth and in archival material of human growth plates. In vitro and ex vivo experiments are performed using the chondrogenic cell line ATDC-5 and cultured metatarsals of wild type, PTHrP -/- and PTH/PTHrP-receptor -/- mice. PTHrP target genes will be identified using DNA microarray technology using both commercially available and custom made cDNA chips. Adenoviral mediated gene transfer will be used to manipulate the expression of receptor for members of the TGFß/BMP-superfamily and estrogen (e.g. mock, wild type, constituteively active, dominant negative). The effects of tese manipulations on the PHTrP/Ihh-feedback loop will be examined at the mRNA level using custom made cDNA chips, at the level of signal transduction by studying the activation state of cytoplasmic signal transduction intermediates, and at the level of transcriptional activation using artificial promotor reporter constructs. The relevance of the findings will be tested in previously collected epiphyseal plates of gonadectomized growing rats or of immature rats supplemented with various sex-steroieds. This material is well characterized with respect to various parameters regarding growth allowing direct correlations between the expression of the candidate tgenes and longitudinal growth. Furthermore, findings will be extended to the human situation by analysing archival growth plates of lethal skeletal dysplasias and of children who have undergone orthopaedic surgery. The results obtained in this study will extent our knownledge on the molecular mechanisms by which longitudinal growth is regulated at the level of the epiphyseal plate and growth plate closure is induced. As such the results will help in the rational design of novel diagnostic tests and growth promoting strategies for growth retarded patients who do not benefit from currently available therapies.

From PubMed study HERE

Journal of Bone and Mineral Metabolism

March 2002, Volume 20, Issue 2, pp 83-90

Human PTH (1–34) induces longitudinal bone growth in rats

Taishi Ogawa, Hiroshi Yamagiwa, Tadashi Hayami, Zhang Liu, Kuan-Yu Huang, Kunihiko Tokunaga,Takehiro Murai, Naoto Endo

Abstract.

The growth plate is a specialized structure that is responsible for longitudinal bone growth (LGR). Growth plate organization is altered with loading in rats. Parathyroid hormone (PTH) is known to induce mitogenic effect on chondrocytes in vitro. Type I PTH/PTH related peptide (rP) receptor is expressed in growth plate cartilage in rats. We therefore investigated the effect of PTH administration on the organization and longitudinal growth rate of the growth plate in rats. We also investigated the effect of PTH on the changes induced by unloading in the organization and growth of the growth plate. Thirty 6-week-old and 30 15-week-old male Sprague-Dawley rats were randomly assigned to five groups (n = 6 per group), i.e., basal controls, control (i.e., normally loaded), PTH-treated control (i.e., PTH-treated under normal loading), unloaded, and PTH-treated under unloading. PTH-treated animals received human PTH (1–34) at a dose of 80 μg/kg per day five times per week for 3 weeks, for the duration of unloading. In young loaded rats treated with the systemic administration of PTH, growth plate thickness, chondrocyte number, and LGR were increased in the proximal tibiae compared with findings in young loaded rats without PTH administration. Hindlimb unloading induced a reduction in growth plate thickness, chondrocyte number, and LGR. In young rats, systemic administration of PTH partly prevented these changes induced by unloading. These preventive effects of PTH were observed only in young rats; not in adult rats. These results show that the systemic administration of PTH stimulates longitudinal bone growth, and diminishes the reduction in growth plate growth induced by unloading in young rats.

From PubMed study HERE

Histol Histopathol. 2000 Jul;15(3):957-70.

Recent studies on the biological action of parathyroid hormone (PTH)-related peptide (PTHrP) and PTH/PTHrP receptor in cartilage and bone.

Amizuka N, Henderson JE, White JH, Karaplis AC, Goltzman D, Sasaki T, Ozawa H.

Source

Department of Oral Anatomy, Niigata University Faculty of Dentistry, Japan. amizuka@dent.niigata-u.ac.jp

Abstract

Mice with a targeted deletion of parathyroid hormone (PTH)-related peptide (PTHrP) develop a form of dyschondroplasia resulting from diminished proliferation and premature maturation of chondrocytes. Abnormal, heterogeneous populations of chondrocytes at different stages of differentiation were seen in the hypertrophic zone of the mutant growth plate. Although the homozygous null animals die within several hours of birth, mice heterozygous for PTHrP gene deletion reach adulthood, at which time they show evidence of osteopenia. Therefore, PTHrP appears to modulate cell proliferation and differentiation in both the pre and post natal period. PTH/PTHrP receptor expression in the mouse is controlled by two promoters. We recently found that, while the downstream promoter controls PTH/PTHrP receptor gene expression in bone and cartilage, it is differentially regulated in the two tissues. 1alpha,25-dihydroxyvitamin D3 downregulated the activity of the downstream promoter in osteoblasts, but not in chondrocytes, both in vivo and in vitro. Most of the biological activity of PTHrP is thought to be mediated by binding of its amino terminus to the PTH/PTHrP receptor. However, recent evidence suggests that amino acids 87-107, outside of the amino terminal binding domain, act as a nucleolar targeting signal. Chondrocytic cell line, CFK2, transfected with wild-type PTHrP cDNA showed PTHrP in the nucleoli as well as in the secretory pathway. Therefore, PTHrP appears to act as a bifunctional modulator of both chondrocyte proliferation and differentiation, through signal transduction linked to the PTH/PTHrP receptor and by its direct action in the nucleolus.

PMID:  10963138 [PubMed – indexed for MEDLINE]

From PubMed study HERE

The parathyroid hormone-related protein and Indian hedgehog feedback loop in the growth plate.

Kronenberg HM, Chung U.

Source
Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.

Abstract

Since I am temporarily living in the Far East, first in South Korea, and now China, I do read and watch a lot of news of the local nations. One news that has been going around the Korean airwaves is about one of the most famous Korean singers in the last decade, a female singer that goes by the name of Boa.

Recently, maybe a few months ago, the singer came on in a public show to express her regret at her short stature (source HERE).

Singer BoA expressed her regret over her short height.

BoA revealed through her Twitter on September 18th, “If I could go back to my teens…I would drink so much milk…I want to return :’(”

BoA also wrote, “I’m going to listen to Eun Ji Won‘s ’160′* while sleeping ^^ good night ^^”

*(160 cm is about 5.25 ft)

Fans who visited BoA’s Twitter responded with comments like, “Honest national singer“, “You’re still pretty even if you’re small“, and “If you’re tall also, you’d be too perfect~“.

Meanwhile, BoA will reveal her repackage album, “Copy & Paste“, through KBS Music Bank on the 24th.

Source: Newsen

From Soompi website HERE…

Me: I guess even the best and most famous of us still might feel small. Will we never be satisfied with who we are? 

What are the bone growth factors?

Me: I am going to find out what are the primary, and the most influential bone growth factors by using four main scientific papers published in journals.

1. From PubMed, US National Library of Medicine, National Institute of Health. Link HERE.

Clin Orthop Relat Res. 1991 Feb;(263):30-48.

Bone growth factors.

Here is a nice quick tip I learned a few days ago after listening to a podcast where a consultant Olivia Fox Cabane was interviewed on what makes a person charismatic and how to create charisma in their persona through learning about postures, body language, and attitude.

As for the part which talks about how to create Charisma, there are 3 elements she gives.

1. Presence

2. Power

3. Warmth

I don’t want to focus on the specifics on what to do to display these three elements which Cabane says exhibit charisma but I do want to mention that she did state that a person can make themselves look and appear taller by doing 4 main things.

1. Stand up with a straight posture

2. Puff out the chest by breathing in the stomach

3. Lower the eyes gaze towards the downward direction

4. Put your hands behind your back.

I would guess that just these 4 tips will probably make a person especially a man, look dominant, powerful, at at least 1-2 inches taller.

This is a question which I have wanted to answer for the longest time, “What is the highest theoretical height of the human species?”

The main way I wanted to answer this question was to use physics principles and try to calculate the most reasonable answer.

First, let’s review the legends and stories of cultures which talk about giants, creatures which are said to be even hundreds of feet tall. Let’s assume that those stories of bipedal creatures are exaggerations and that if the stores were based on real life humanoid creatures, then the actual height was probably less than 30 feet.

We know that the tallest recorded human is Robert Wadlow, who right before the died at 22 was nearly up to the 9 feet point. So we can say with certainty that humans can get to at least 9 feet in height. However, as most people like Wadlow are, they seemed to have suffered from problems of their pituitary gland, whether is was from hypertrophy or tumor compressions.

We know that almost Everyone who is passed the 7′ 6″ point has had a history of pituitary gland issues. There are a few people who seem to grow to that height from genetics but they are extremely rare. Plus, even if the person does reach that height from genetics, it seems that they are more prone to injuries, especially in the joints like the knees, ankles, and hips. This suggest to us that the weakest areas of the human body will be where the answer can be reached.This means that even if people do reach enormous height from genetics, they may not traditionally have lived long enough or been healthy enough to find a mate and reproduce to mass on the tallness gene.

Since the majority of humans are of a height in the middle of the distribution bell curve, the environment would be made and tailored for people in the middle, putting people who are too tall at a disadvantage.

Humans are bipedal creatures so if we look for other species which move in bipedal fashion, we can make better and more accurate guesses. We have heard stories of Bigfoot and Sasquatch who are usually reported around the 7-9 feet mark. Many anthropologist say that is is possible the Bigfoot of Cryptozoological fame is really the modern development of a very distance primate relative of the human, Gigantopithecus Blacki which is estimated to be up to 10 feet tall.

If we then take into consideration ancient Native American stories of red haired giants and the occasional giant skeleton that seems to be found, we can state with some confidence that a height of 12 feet is totally possible.

If we were to extend the definition of research further, we can look for the largest bipedal animals that have ever lived on Earth as a model. There really is almost no mammals or animals today that only stands on two legs, but four. Creatures like the Elephant and Giraffe are tall but their huge weight is distributed across four limbs. We have to look at dinosaurs and see how tall they reached.

From resource 1, we find that the tallest herbivore dinosaur was the Shantungosaurus standing approximately 25 feet tall.

From resource 2, we find that the tallest carnivore dinosaur was the Carcharodontosaurus standing at 12 feet around the hips and estimably to be maybe 20 feet tall.

If we remember that the dinosaurs went through a sort of evolutionary arms race in terms of growing larger and larger, I would guess that the herbivores and carnivores evoked along with each other until they reached was is theoretically possible for animals on earth.

The maximum possible height for any bipedal animal on earth should be around the 30 feet mark, because anything over it will have cartilage problems in the joints of the knees when it moves. As far as biologist know animals today, most large creatures on land have their body defined by bones, and the bones are not flexible or elastic so movement in all three 3 dimensions of space requires the need for joints. Joints are flexible but their flexibility come a the cost of not being as strong as the actual bone parts.

From physics, remember principle 1, As a creature increase in height in 1 dimension, their mass which is proportional to their weight which is proportional to their volume increases in 3 dimensions, which their surface areas increases by 2 dimensions. This means that as any creature gets taller, their weight will increase at a geometric rate which is a factor of the height increase multiplied by itself 2 times over as in delW=(delH)^3.

As a creature gets taller, they take on more mass in the top and bottom. Their knees and lower joints have more pounds per square inch extorted. If we remember from our studies of human femur cortical bone strength, it is just as strong as steel, with a maximum compressive strength of being over 200 Mpa. This value was found from human femur bones being tested on mechanical instruments which exerted a compressive loading force on the bones.

Assume the human body is just a geometric cylindrical shaped weight at a proportion of 1:5.5 for width: height since average human gait is about 1 feet and average human height is about 5 and a half feet tall, and put two rods to support it.

From source 1, we know the average human body density. – Average human body density. 1400 kg/m3 = 1.4 g/cm 3

since the we can first choose a value of say 4 feet width getting 22 feet in height assuming depth=width, then we can calculate the volume with 4*4*22 which we can then divide by the density to find the weight of a human that is 22 feet tall. That weight is then equated with 2 times the loading force of a leg limb which has a width assumed to be 1/4 th the torso length of 4 feet (which is 1 feet). We know that the human long bones are not solid bone but hollow so we can use the formula

R1^2*pi-R2^2*pi= Area of single femur bone. Another assumption is to assume the outer cortical thickness is possibly the same thickness as the inter medullary cavity, so about 2  inches thick. Area of bone is around 24 area units (assume 3^2*pi-1^2*i). since the maximum compressive force is around 200 MPa of each area unit, we multiple the two limb areas by the maximum compressive load, which is a force/area unit. and cam then compare the two values, the weight of the entire creature to the maximum compressive force the two hollow limbs can handle. This calculation can be easily done using any computational tool. The value which will eventually be reached from recursive convergent calculation should be far higher than the 30 feet that nature allows. However, this is only from comparing the bone loading capacity, not the joint or cartilage loading capacity, which is far less.

Another calculation with the maximum compressive strength of hyaline cartilage will be done but the overall method has already been explained.

The 2nd major calculation is to see just how hard the heart would have to do work to be able to pump the amount of blood needed to the body to make everything work. We know that atmospheric pressure s about 760 mmHg. We also know the density of human blood. since the heart is at the center of the human body, we can take half of a height, say for a 20 feet tall beast and find out how much work would be needed to pump up to the center of the body.

From wikipedia,…Blood accounts for 8% of the human body weight,^[3] with an average density of approximately 1060 kg/m³, very close to pure water’s density of 1000 kg/m³.^[4] The average adult has a blood volume of roughly 5 liters (1.3 gal)

The amount of blood from 5 liters has to be multiplied by the increase in height factor, which is a cubed function. Once the amount of total volume of blood is found in a 20 feet tall bipedal animal, we assume more than half of that amount (say 70%) must go from the legs and arms up to the heart, The femoral arteries and arm arteries are all attached to the heart, but a significant amount of the blood must go to the brain to supply it with the needed amount of oxygen. The work is defined by a heart pump is by knowing the dimeter, a constant function, and the flow velocity, Flow velocity is from taking the entire blood volume, knowing the total surface area of the blood vessels which is found from multiplying by the same increase factor, and knowing how many times in a minute (or the rate) which the heart must pump through the system .depending on how we want to assume the type of pump the heart may be, we use different factor constants to know the amount of work the heart does. For the heart to do the type of work, we must figure out whether such a speed is possible from looking at the amount of food or chemical energy goes into the body. At this point, I am not sure how to find certain value to make that calculation.

My final guess is that humans are limited by their cartilage in the joints, and and blood pumping upwards against the force of gravity which will limit them to less than 20 feet, but I would guess 15 feet in maximum height is completely reasonable.

Something that I have also been interested about for a long time was to ask whether we could possibly alter or increase the number of insulin growth factor receptors in the growth plates to possibly increase height.

The thing I have learned so far is that the effect of IGF-1 is both systemic and local in nature. Also it seems that both the hGH and the IGF-1 both can work to stimulate the growth plate chondrocytes from the study “IGF-Independent Effects of Growth Hormone on Growth Plate Chondrocyte Function”

From the Wikipedia article on the Insulin-like Growth Factor 1 Receptor…

“…is a protein found on the surface of human cells. It is a transmembrane receptor that is activated by a hormone called Insulin-like growth factor 1 (IGF-1) and by a related hormone called IGF-2. It belongs to the large class of tyrosine kinase receptors. This receptor mediates the effects of IGF-1, which is a polypeptide protein hormone similar in molecular structure to insulin. IGF-1 plays an important role in growth and continues to have anabolic effects in adults – meaning that it can induce hypertrophy of skeletal muscle and other target tissues. Mice lacking the IGF-1 receptor die late in development, and show a dramatic reduction in body mass, testifying to the strong growth-promoting effect of this receptor. Mice carrying only one functional copy of igf1r are normal, but exhibit a ~15% decrease in body mass.”

From PubMed study “IGF-1R signaling in chondrocytes modulates growth plate development by interacting with the PTHrP/Ihh pathway.”

Abstract

Systemic derangements and perinatal death of generalized insulin-like growth factor 1 (IGF-1) and IGF-1 receptor (IGF-1R) knockout mice preclude definitive assessment of IGF-1R actions in growth-plate (GP) chondrocytes. We generated cartilage-specific Igf1r knockout ((Cart) Igf1r(-/-)) mice to investigate local control of chondrocyte differentiation in the GP by this receptor. These mice died shortly after birth and showed disorganized chondrocyte columns, delayed ossification and vascular invasion, decreased cell proliferation, increased apoptosis, and increased expression of parathyroid hormone-related protein (Pthrp) RNA and protein in their GPs. The increased Pthrp expression in the knockout GPs likely was due to an increase in gene transcription, as determined by the increased activity of a LacZ reporter that was inserted downstream of the endogenous PTHrP promoter and bred into the knockout mice. To circumvent the early death of (Cart) Igf1r(-/-) mice and investigate the role of IGF-1R during postnatal growth, we made tamoxifen (Tam)-inducible, cartilage-specific Igf1r knockout ((TamCart) Igf1r(-/-)) mice. At 2 weeks of age and 7 to 8 days after Tam injection, the (TamCart) Igf1r(-/-) mice showed growth retardation with a disorganized GP, reduced chondrocyte proliferation, decreased type 2 collagen and Indian Hedgehog (Ihh) expression, but increased expression of PTHrP. Consistent with in vivo observations, in vitro knockout of the Igf1r gene by adenoviral expression of Cre recombinase suppressed cell proliferation, promoted apoptosis, and increased Pthrp expression. Our data indicate that the IGF-1R in chondrocytes controls cell growth, survival, and differentiation in embryonic and postnatal GPs in part by suppression of Pthrp expression.

Analysis & Interpretation:

We see from the Abstract that the IGF1R is needed for at least the formation of the organization of the chondrocyte columns which is absolutely critical for the formation of any length of bone, to get the timing of ossification correctly, cell proliferation, and a slow rate of chondrocyte apoptosis. It seems that when mice which are bred to have the IGF1r gene knockout caused quick death. All of the essential chondrocyte and growth plate compounds like collagen type II, Ihh, were all lower but the PTHrP expression was higher. This result is surprising to me because of a previous post where I wrote that maybe the way to cause regenerated growth plates was to use the higher expression of PTHrP. Maybe I was wrong in believing that increased PTHrP was a good thing.

Implications:

This post shows the real reason why it is important to study every and learn as much as possible about the system we are looking at because the information from one study may correct, disapprove, and change our previous wrong assumptions and ideas. At this point, I would have to say that PTHrP expression may not be useful for chondrocyte proliferation, column formation, etc.

From the Technical Book “Pediatric Bone: Biology & Diseases” pg. 72 by Francis H. Glorieux, John M. Pettifor, Harald Jüppner I have taken 2 clips of the information. It shows that the receptors of the IGF-1 is found on the cell surface of the chondrocytes of the growth plate.

There is 2 types of IGF1R, Type 1 and Type 2. The type 1 is found mostly in the proliferative zone of the growth plate while the Type 2 type is found in all of the zones of maturation in the growth plate. It would seem that there is some ability in the IGF1R in suppresion PTHrP (Parathyroid hormone related protein) expression.