DoorHandle5
Iron
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You haven’t responded to this eitherDexter
PrettyBoyMaxxing
For the proliferating zone, I sent this to my boy cuz I have no retort honestly, he said this:
the proliferating zone, once resuscitated, will build a gap between the osteoblasts and the resting zone's stem cells. once the gap is created by these columnar chondrocytes stacking one atop the other, the PTHrP gradient will naturally become great enough that prehypertrophic and hypertrophic zones can develop. these zones develop organically without the need for us to act. the key is the proliferating zone. if that is resuscitated, all bets are off. the gradients that are vital develop naturally by virtue of spacing. hormones need to be managed (AI's), but the zones themselves will otherwise provide the signals they all need to maintain themselves.
that written, there's a plethora of research done examining what transpires when SOX, PTHrP, and SMO agonists (or other Hedgehog pathway activators or enhancers) are applied to the growth plates of animal models, and from these studies, we can paint a picture of how plastic and flexible the system is, and how readily progenitors in the resting zone (mesenchymal stem cells) operate to generate chondrocytes if given the right circumstances. hell, in rabbits, they've even studied dissection of the growth plate and aberrant reinsertion (perpendicular to the original direction) and found that the growth plate would add length along the width of the bone. it demonstrates that the stem cells in the resting zone are polarized, and they will generate columns even if oriented in aberrant directions. they've studied constitutive Hedgehog activation (constantly active Hedgehog signaling) in murine models, done via PTCH1 knockout, and found that cartilaginous "islands" (ectopic cartilage) can be produced off the resting zone's chondroprogenitors. these studies elucidate that influencers like PTHrP, SOX, and even Hedgehog molecules can whip up a proliferative response dedicated to endochrondral ossification in theory. the trick is now seeing if we can harness that in vivo, which is admittedly extremely challenging to do! I will never take away from how difficult this is when local application of these agents is not possible. that is the crux of the problem to me. give me a way to ensure that the stem cell niche is constantly and specifically inundated with PTHrP & SOX proteins, and I will be much more optimistic. currently, no recourse therein. systemic circulation is the only hope.
I’m trying to recreate resting & proliferating zones. That’s the fundamental mission, and if there are remnant stem cells present, enough stimulation with PTHrP & SOX could potentially inhibit osteogenic pressures and induce the chondrogenesis necessary to recreate a proliferating zone that can build space between the resting zone and the osteoblast-containing front.
if I'm not mistaken, I think there might actually be research currently ongoing in which the researchers are seeking to cause transdifferentiation (from osteoblast to chondrocyte) of the cells of the fused epiphysis. my fixation is on a parallel strategy that focuses instead on multipotent stem cells that may already be present. these cells obviously have the potential to differentiate chondrogenically if inundated with the right factors.
the premise is that a sliver of cartilage would need to be generated first. this will be the resting zone. if that resting zone can survive with continuous PTHrP & SOX pressure, the proliferating zone ensues. with continuing chondrogenic pressure, the proliferating zone expands enough to buy the resting zone enough of a buffer to no longer require the inundation of PTHrP & SOX proteins. at this point, exogenous PTHrP supply is abrogated, and a natural PTHrP gradient develops that allows for prehypertrophic and hypertrophic zones to develop distal to the resting zone.
and just to reiterate becuz we seem to continuously come circling back to the fact that a functional growth plate has prehypertrophic and hypertrophic zones, as well as the proliferating & resting zones that I've chosen to fixate on. the point is that these former zones will develop organically once PTHrP provision is ceased because of the AMPLE osteogenic pressure provided by the cells of the trabecular bone below the growth plate. PTHrP & SOX generated by chondroprogenitors of the resting zone will not diffuse far enough away from the resting zone, and the consequent gradient will allow for chondrocyte hypertrophy to begin. there's no need for us to manipulate anything to facilitate the development of prehypertrophic and hypertrophic zones; the bone will ensure that that happens, anyway.
the bone WILL NOT allow for a proliferating zone to develop sans heavy SOX pressure, though. that is the part we have to play God on. hence, inundation with abaloparatide that can induce SOX activity. this ensures MSC renewal (PTHrP) and chondrogenesis at the expense of osteogenesis (SOX)
Ur all talk bro



