Tuesday, February 22, 2011

Grow Taller by Inhibiting Actin Polymerization

Inhibiting actin polymerization may be a way to force mesenchymal stem cells to commit to a chondrogenic lineage.  The actin cytoskeleton plays a huge role in mechanosensativity(or the sensativity of cells to load).  Compounds or other factors that all us to manipulate the actin cytoskeleon may help restore sensitivity to methods such as lateral synovial joint loading and also other loading regimes(like weight lifting).  There are compounds that inhibit actin polymerization.  Could they be a way to increase height growth?

Synthetic triterpenoids target the Arp2/3 complex and inhibit branched actin polymerization.

"Synthetic triterpenoids are anti-tumor agents that affect numerous cellular functions including apoptosis and growth inhibition. Here, we used mass spectrometric and protein array approaches and uncovered that triterpenoids associate with proteins of the actin cytoskeleton, including actin-related protein 3 (Arp3). Arp3, a subunit of the Arp2/3 complex, is involved in branched actin polymerization and the formation of lamellipodia. 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO)-Im and CDDO-Me were observed to 1) inhibit the localization of Arp3 and actin at the leading edge of cells, 2) abrogate cell polarity, and 3) inhibit Arp2/3-dependent branched actin polymerization[CDDO and CDDO-Me can help you grow taller by inhibiting actin polymerization but it would probably need to be controlled as you need cell migration sometimes]. We confirmed our drug effects with siRNA targeting of Arp3 and observed a decrease in Rat2 cell migration. Taken together, our data suggest that synthetic triterpenoids target Arp3 and branched actin polymerization to inhibit cell migration."

Inhibiting cell migration may be one way to achieve mesenchymal stem cell condensation, one of the key steps for height growth.  However,  the application of CDDO or CDDO-Me would have to be precise as cell migration is needed to fight infections for instance.  You also need initial cell migration to get the stem cells all in one spot.

AlphaE-catenin regulates actin dynamics independently of cadherin-mediated cell-cell adhesion.

"alphaE-catenin binds the cell-cell adhesion complex of E-cadherin and beta-catenin (beta-cat) and regulates filamentous actin (F-actin) dynamics. In vitro, binding of alphaE-catenin to the E-cadherin-beta-cat complex lowers alphaE-catenin affinity for F-actin, and alphaE-catenin alone can bind F-actin and inhibit Arp2/3 complex-mediated actin polymerization. In cells, to test whether alphaE-catenin regulates actin dynamics independently of the cadherin complex, the cytosolic alphaE-catenin pool was sequestered to mitochondria without affecting overall levels of alphaE-catenin or the cadherin-catenin complex. Sequestering cytosolic alphaE-catenin to mitochondria alters lamellipodia architecture [lamellipodia are a part of the actin cytoskeleton on the outer portion of the skull, altering this architecture may also alter actin cytoskeleton sensitivity] and increases membrane dynamics[increase in membrane activity which would help with chondrogenic differentiation] and cell migration without affecting cell-cell adhesion. In contrast, sequestration of cytosolic alphaE-catenin to the plasma membrane reduces membrane dynamics. These results demonstrate that the cytosolic pool of alphaE-catenin regulates actin dynamics independently of cell-cell adhesion."

"During development, cells migrate to specific sites and then, upon contact with other cells, become stationary and differentiate into tissues"<-We want stem cells to migrate to one area, become stationary and differentiate into chondrocytes, so we want to only inhibit cell migration in one specific area(the area of the new growth plate)

"Membrane activity at the leading edge of cells, driven largely by Arp2/3 complex–mediated nucleation of branched filamentous actin (F-actin) networks, promotes cell movement and is involved in the initiation of intercellular contacts. After contact initiation in simple epithelial cells, the actin network associated with the plasma membrane is reorganized and eventually forms bundled filaments oriented parallel to the lateral contact between cells. These changes in actin organization coincide with dampening of membrane dynamics and cell migration and the establishment of strong cell–cell adhesion"<-just condensing the cells by itself by a mechanism such as Lateral Synovial Joint Loading induced hydrostatic pressure may be enough to inhibit cell migration

Actin polymerization is important but you need to inhibit the Arp2/3 complex at a specific point.  You'd want a localized inhibition where you'd want the new growth plate.  It's just too complex to be achieved right now.  Just keep doing LSJL like you're doing and cells should migrate when they're supposed to and adhese when they're supposed to.

Profilin1 regulates sternum development and endochondral bone formation.

"[The] actin cytoskeleton system is regulated by critical modulators including actin binding proteins. Among them, profilin1 (Pfn1) is a key player to control actin fiber structure and it is involved in a number of cellular activities such as migration. During the early phase of body development, skeletal stem cells and osteoblastic progenitor cells migrate to form initial rudiments for future skeletons. During this migration, these cells extend their process based on actin cytoskeletal rearrangement to locate themselves in an appropriate location within microenvironment.  Here, we examined the role of Pfn1 in skeletal development using a genetic ablation of Pfn1 in MPCs by using Prx1-Cre recombinase. We found that Pfn1 deficiency in MPCs caused complete cleft sternum. Notably, Pfn1 deficient mice exhibited absence of trabecular bone in the marrow space of appendicular long bone. This phenotype is location specific, as Pfn1 deficiency did not largely affect osteoblasts in cortical bone. Pfn1 deficiency also suppressed longitudinal growth of long bone[would overepxression of Pfn1 increase height?]."

Specific changes to the mechanism of cell locomotion induced by overexpression of beta-actin.

"Overexpression of beta-actin is known to alter cell morphology. Here we show that overexpressing beta-actin in myoblasts has striking effects on motility, increasing cell speed to almost double that of control cells. This occurs by increasing the areas of protrusion and retraction and is accompanied by raised levels of beta-actin in the newly protruded regions. These regions of the cell margin, however, show decreased levels of polymerised actin, indicating that protrusion can outpace the rate of actin polymerisation in these cells. Moreover, the expression of beta*-actin (a G244D mutant, which shows defective polymerisation in vitro) is equally effective at increasing speed and protrusion. Concomitant changes in actin binding proteins show no evidence of a consistent mechanism for increasing the rate of actin polymerisation in these actin overexpressing cells. The increase in motility is confined to poorly spread cells in both cases and the excess motility can be abolished by blocking myosin function with butanedione monoxime (BDM).  The additional motility shown by cells overexpressing beta-actin appears not to result from an increase in the rate of actin polymerisation but to depend on myosin function. This suggests that the additional protrusion arises from a different mechanism. We discuss the possibility that it is related to retraction-induced protrusion in fibroblasts. In this phenomenon, a wave of increased protrusion follows a sudden collapse in cell spreading."

Osteopontin Promotes Mesenchymal Stem Cell Migration and Lessens Cell Stiffness via Integrin β1, FAK, and ERK Pathways.

Osteopontin is typically a cell associated with osteoblasts but if it reduces in the dissolution of the actin cytoskeleton maybe it can enhance chondrogenesis.

"The expression of osteopontin (OPN){LSJL upregulates osteopontin} is elevated in response to injury and inflammation [and has a] role [in] rat bone marrow-derived mesenchymal stem cells (rMSCs)-directed migration. OPN activated focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK) signaling pathways by the ligation of integrin β1 in rMSCs. Inhibitors of FAK and ERK pathways inhibited OPN-induced rMSCs migration, indicating the possible involvement of FAK and ERK activation in OPN-induced migration in rMSCs. OPN reduced cell stiffness in rMSCs via integrin β1, FAK, and ERK pathways, suggesting that the promotion of rMSCs migration might partially be contributing to the decrease in cell stiffness stimulated by OPN. To further examine the role of OPN on cell motility and stiffness, actin cytoskeleton of rMSCs was observed. The reduced well-defined F-actin filaments and the promoted formation of pseudopodia in rMSCs induced by OPN explained the reduction in cell stiffness and the increase in cell migration. OPN binding to integrin β1 promotes rMSCs migration through the activation of FAK and ERK pathways, which may be attributed to the change in cell stiffness caused by the reduction in the amount of organized actin cytoskeleton."

"Transforming growth factor β (TGF-β) can promote MSC differentiation into either smooth muscle cells (SMCs) or chondrogenic cells. Here we showed that the stiffness of cell adhesion substrates modulated these differential effects. MSCs on soft substrates had less spreading, fewer stress fibers and lower proliferation rate than MSCs on stiff substrates. MSCs on stiff substrates had higher expression of SMC markers α-actin and calponin-1; in contrast, MSCs on soft substrates had a higher expression of chondrogenic marker collagen-II and adipogenic marker lipoprotein lipase (LPL). TGF-β increased SMC marker expression on stiff substrates. However, TGF-β increased chondrogenic marker expression and suppressed adipogenic marker expression on soft substrates, while adipogenic medium and soft substrates induced adipogenic differentiation effectively. Rho GTPase was involved in the expression of all aforementioned lineage markers, but did not account for the differential effects of substrate stiffness. In addition, soft substrates did not significantly affect Rho activity, but inhibited Rho-induced stress fiber formation and α-actin assembly. MSCs on soft substrates had weaker cell adhesion, and that the suppression of cell adhesion strength mimicked the effects of soft substrates on the lineage marker expression. These results provide insights of how substrate stiffness differentially regulates stem cell differentiation, and have significant implications for the design of biomaterials with appropriate mechanical property for tissue regeneration."

"matrix stiffness did not significantly affect the activation of Smad2/3 in the absence or presence of TGF-β, suggesting that matrix stiffness regulated mechanotransduction in parallel to Smad2/3 signaling."

"RhoA activation significantly induced the expression of SMC markers on stiff substrates, and to a lesser extent on soft substrates. However, RhoA activation also significantly increased the expression of collagen-II and LPL on a soft substrate"

"RhoA activation drastically induced stress fibers and the assembly of α-actin into fibers in cells on stiff but not soft substrates, suggesting that soft substrates limit the function of Rho activity."

"focal adhesions of cells on soft substrates were fewer and smaller"

"MSCs [were] derived from young and old Sprague-Dawley rats. MSC concentration in bone marrow declines with age [and] their function is altered, especially their migratory capacity and susceptibility toward senescence. High-resolution two-dimensional electrophoresis of the MSC proteome, under conditions of in vitro self-renewal as well as osteogenic stimulation, identified several age-dependent proteins, including members of the calponin protein family as well as galectin-3.  Age-affected molecular functions are associated with cytoskeleton organization and antioxidant defense. [Aged MSCs have] lower actin turnover and diminished antioxidant power. Two main reasons for the compromised cellular function of aged MSCs: (a) declined responsiveness to biological and mechanical signals due to a less dynamic actin cytoskeleton and (b) increased oxidative stress exposure favoring macromolecular damage and senescence."

"[Hematopoietic stem cell] numbers do not necessarily decline with age, but for that cellular function is clearly compromised, for example with regard to mobilization, homing, and lineage choice. Cellular aging of HSCs has been attributed to various mechanisms that exhibit a partial cause and effect relationship to each other. For example, telomere shortening, as a cell-intrinsic trigger for replicative senescence, was shown to be associated with impaired HSC function due to reduced long-term repopulation capacities and increased genetic instability"

"Lifelong dietary restriction increases HSC frequencies and improved HSC function. The self-renewal capacity of HSCs depends on the control of oxidative stress, and additionally, progressive bone marrow failure is associated with elevated reactive oxygen species (ROS). Concordantly, treatment with antioxidative agents has prevented bone marrow failure and restored the reconstitutive capacity of HSCs deficient of Atm, whose gene product inhibits oxidative stress."

Vimentin and Transgelin two aging related actin cytoskeleton proteins are upregulated by LSJL.  The two proteins are also upregulated in aging.

"loss of galectin-3 has been associated with altered Indian hedgehog expression pattern at the growth plate, increased cell death of hypertrophic chondrocytes, and uncoupling of growth plate vascularization"

Decreasing F-actin is pro-chondrogenic.

Cyclic stretching promotes collagen synthesis and affects F-actin distribution in rat mesenchymal stem cells.

"Rat BMSC were harvested from adult rats and cultured to passage 4. Then the cells were seeded onto a silicone{silicone varies in stiffness} membrane loaded with an uniaxial cyclic stretching (10%, 1 Hz) during 3, 6, 12, 24 and 36 h. Stretching enhanced the synthesis of collagen types I and III in BMSC after 24 h stimulation. However, a decrease in fluorescence density of F-actin was observed after the stretching in a time dependent manner. The F-actin filaments seemed much thinner than those of static cells. Cyclic stretching [favors] the synthesis of collagen types I and III, but decreased the amount of F-actin in the BMSC."


  1. Tyler, i cant login the forum...

    I have a real important question, hope you are able to answer it.

    How can we load the upper epiphysis of the FEMUR??
    if you google it for images, you'll see that the epiphysis of the femur(the upper one)is "inside" the leg.. the part u said we should load, that we can reach, is not the epiphysis!

    what can you say about this??

  2. There's not known way to load the femur at this point but loading the knee may affect the epiphysis of the femur.

    However, by definition of shear strain some of the fluid flow may decrease due to resistance before it can reach the upper epiphysis. Eventually, there may be a way to do it using the piezoelectric current. But for now just load the lower part of the femur and hope that the fluid flow flows all the way to the upper epiphysis to increase hydrostatic pressure.