IRS-1 stands for insulin related substrate 1. The key to inducing change in the body is inhibiting the bodies negative feedback mechanisms. IRS-1 is not involved in negative feedback mechanisms but it still relates to mesenchymal stem cells and growing taller.
Subcellular localization of IRS-1 in IGF-I-mediated chondrogenic proliferation, differentiation and hypertrophy of bone marrow mesenchymal stem cells.
"Bone marrow derived mesenchymal stem cells (BM-MSC) can differentiate into chondrocytes. The activated type 1 insulin-like growth factor receptor (IGF-IR), interacting with the insulin receptor substrate-1 (IRS-1){LSJL downregulates IRS-1}, can induce cancer cell proliferation and transformation. In cancer or transformed cells, IRS-1 has been shown to localize in the cytoplasm where it activates the canonical Akt pathway, as well as in the nucleus where it binds to nuclear proteins. IGF-I has distinct time-dependent effect on primary BM-MSC chondrogenic pellets: initially (2-day culture), IGF-I induces proliferation; subsequently, IGF-I promotes chondrocytic differentiation (7-day culture). In the present study, by using MSC from the BM of IRS-1(- / - ) mice we show that IRS-1 mediates almost 50% of the IGF-I mitogenic response and the MAPK-MEK/ERK signalling accounts for the other 50%. After stimulation with IGF-I, we found that in 2-day old human and mouse derived BM-MSC pellets, IRS-1 (total and phosphorylated) is nuclearly localized and that proliferation prevails over differentiation. The IGF-I mitogenic effect is Akt-independent. In 7-day MSC pellets, IGF-I stimulates the chondrogenic differentiation of MSC into chondrocytes, pre-hypertrophic and hypertrophic chondrocytes and IRS-1 accumulates in the cytoplasm. IGF-I-dependent differentiation is exclusively Akt-dependent. IGF-I induces a temporally regulated nuclear or cytoplasmic localization of IRS-1 that correlate with the transition from proliferation to chondrogenic differentiation."
"IGF binding to the IGF-IR results in autophosphorylation of the receptor and activation of its intrinsic tyrosine activity that, in turn, leads to the phosphorylation of multiple substrates, including insulin receptor substrate-1 (IRS-1)""IRS-1 is a docking protein for the IGF-IR which binds to and activates phosphatidylinositol-3-kinase (PI3-K)"
"IGF-I dependent MAPK signalling proceeds from IGF-IR phosphorylated Shc proteins leading to the sequential activation of mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 (MEK1/2) and extracellular signal-regulated kinase 1/2"
"almost half of the IGF-I proliferative action on MSC is mediated by IRS-1"
"While IRS-1 is nuclearly localized, IGF-I-mediated proliferation prevails over differentiation. The expression of IRS-1, together with MEK/ERK activation, accounts for the IGF-I mitogenic effect that is Akt-independent"
Now if we can inject extraneous IRS-1 it may be possible for supramaximal growth if IRS-1 doesn't provide a negative feedback mechanism to IGF-1.
Leptin increases proliferation of human steosarcoma cells through activation of PI(3)-K and MAPK pathways.
"Serum leptin levels are strongly and directly related to fat body mass (FBM). Bone mineral density (BMD) increases with FBM. Leptin[produced by mainly adipose tissue but also cartilage and bone as well] exerts direct osteogenic effects in vitro.
Saos-2 cell lines were used. Leptin receptor common form (OB-Ra) and long form (OB-Rb) were detected by RT-PCR and immunocytochemistry. PI(3)-K activity was immunoprecipitated using antibodies directed against tyrosine-phosphorylated proteins and IRS-1. The activated form of p42/p44 MAPK was investigated in cytosolic extracts of confluent Saos-2 in response to leptin.
In this study, we tested the hypothesis that leptin might be a mediator linking obesity and bone cell proliferation. Saos-2 cells expressed OB-Ra and OB-Rb. Leptin (10 nmol/L - 2 umol/L) caused a significant increase in the activation of PI (3)-K that was accompanied by an increase in cell proliferation dose dependently based on the [3H]-thymidine incorporation. The specific PI (3)-K inhibitors LY294002 and wortmannin blocked leptin-induced cell proliferation. Interestingly, leptin activated MAPK and the specific MAPK-inhibitor PD98059 blocked DNA synthesis induced by leptin. Leptin may increase bone mass by stimulating osteoblast proliferation through activation of the P1 (3)-K and MAPK signaling pathways[this activation of the MAPK pathways may be beneficial to chondrocytes as well]."
A non-insulin related possibility for the link between being tall and fat. MAPK stands for Mitogen Activated Protein Kinase. P38 is the one most typically associated with height growth. We already know that MAPK is important in chondrocytic differentiation. Although a Leptin mechanism for inducing height would imply a causality between developmental obesity and height gain whereas an increase in insulin sensitivity would only be a correlation between height gain and high bodyfat percentage. But Leptin would not enhance muscle growth whereas insulin would so that would be one way to study the tall and fat connection.
So IRS-1 is important for chondrocyte proliferation and MAPK(P-38) is important for chondrocyte differentiation. It is possible that direct injection of these two substances into the growth plate would enhance height growth barring some negative feedback mechanism.
Here's a grant related to MAPK p38:
EFFECT ON MURINE GROWTH OF BDNF RECEPTOR AND P38 KNOCKOUTS AT THE GROWTH PLATE
"Using large numbers of growth plate chondrocytes isolated from a bovine source, we have identified brain-derived neurotrophic factor (BDNF) as a novel regulator of growth plate maturation, and have begun to examine how BDNF, acting through its receptor TrkB, modulates IGF-I action in growth plate chondrocytes by differentially regulating two MAPK pathways. Growth plate chondrocyte proliferation and differentiation are both dependent on the activation of the classic MAPK, ERK1/2. IGF-I stimulates chondrocyte proliferation via ERK activation, but BDNF inhibits IGF-I-stimulated chondrocyte proliferation. Whereas neurotrophins like BDNF stimulate neuronal cell development by causing sustained ERK activation, BDNF instead inhibits ERK activity in our isolated chondrocytes. Moreover, BDNF activates the p38 MAPK pathway, which has been shown to inhibit proliferation in other cell types. Other groups have implicated p38 in the regulation of growth by showing that p38 inhibition delays chondrocyte maturation. We proposed a model wherein IGF-I-stimulated ERK activation is required for both proliferation and differentiation of chondrocytes, but p38 activation by BDNF is required for the cells to make the transition from proliferation to differentiation. The overall goal of the proposed project is to demonstrate the importance of p38 and TrkB signaling to growth plate development by disrupting their expression in developing chondrocytes, and to further examine the relevant signaling mechanisms in chondrocytes with in vitro studies."<-So we want to inhibit BDNF to grow taller but we're not sure about p38.
According to a personal communication with Hiroki Yokota, the ERK and p38 pathway are involved in LSJL.
MEK/ERK and p38 MAPK regulate chondrogenesis of rat bone marrow mesenchymal stem cells through delicate interaction with TGF-beta1/Smads pathway.
"Chondrogenic differentiation of rat BMSCs was initiated in micromass culture, in the presence of TGF-beta1, for 2 weeks. ERK1/2 and p38 kinase activities were investigated by Western Blot analysis. Specific MAPK inhibitors PD98059 and SB20350 were employed to investigate regulatory effects of MEK/ERK and p38 signals on gene expression of chondrocyte-specific markers, and TGF-beta1 downstream pathways of Smad2/3.
ERK1/2 was phosphorylated in a rapid but transient manner, whereas p38 was activated in a slow and sustained way. The two MAPK subtypes played opposing roles in mediating transcription of cartilage-specific genes for Col2alpha and aggrecan. TGF-beta1-stimulated gene expression of chondrogenic regulators, Sox9, Runx2 and Ihh, was also affected by activity of PD98059 and SB203580, to different degrees. However, influences of MAPK inhibitors on gene expression were relatively minor when not treated with TGF-beta1. In addition, gene transcription of Smad2/3 was significantly upregulated by TGF-beta1, but was regulated more subtly by treatment with MAPK inhibitors."
"JNK has been reported to play only a very minor role in chondrogenesis as JNK phosphorylation is not affected during the process"
"ERK1/2 [may] play a negative role [in chondrogenesis], whereas p38 plays a positive role in chondrogenesis of limb bud mesenchyme initiated in micromass culture"
"Addition of TGF-β1 led to rapid phosphorylation of ERK1/2, which increased on day 1 and peaked on day 3, but then gradually decreased as chondrogenesis proceeded"
"PD98059" inhibits ERK
"SB203580" inhibits p38
"When treated with PD98059 at 10 μm, TGF-β1-induced gene expression of Col2α and aggrecan were significantly enhanced. TGF-β1-induced Col2α mRNA expression was elevated by PD98059 at 1 day of treatment, and was sustained until day 14"
"inhibition of p38 MAPK resulted in substantial reduction in transcription of the cartilage-specific genes"
" the function of ERK1/2 in chondrogenesis may shift in different developmental stages."
"TGF-β1-induced Ihh gene expression was significantly reduced by both PD98059 and SB203580, indicating that both MEK/ERK and p38 pathways are positive regulators of Ihh gene transcription."
No comments:
Post a Comment