Papers by Thomas Doetschman
genesis, 2011
The p75 NTR neurotrophin receptor has been implicated in multiple biological and pathological pro... more The p75 NTR neurotrophin receptor has been implicated in multiple biological and pathological processes. While significant advances have recently been made in understanding the physiologic role of p75 NTR , many details and aspects remain to be determined. This is in part because the two existing knockout mouse models (Exons 3 or 4 deleted, respectively), both display features that defy definitive conclusions. Here we describe the generation of mice that carry a conditional p75 NTR (p75 NTR-FX) allele made by flanking Exons 4-6, which encode the transmembrane and all cytoplasmic domains, by loxP sites. To validate this novel conditional allele, both neural crest-specific p75 NTR /Wnt1-Cre mutants and conventional p75 NTR null mutants were generated. Both mutants displayed abnormal hind limb reflexes, implying that loss of p75 NTR in neural crestderived cells causes a peripheral neuropathy similar to that seen in conventional p75 NTR mutants. This novel conditional p75 NTR allele will offer new opportunities to investigate the role of p75 NTR in specific tissues and cells. genesis 49:862-869, 2011. V
The Journal of Immunology
Previous studies have suggested that oral tolerance induction by low doses of Ag is mediated by i... more Previous studies have suggested that oral tolerance induction by low doses of Ag is mediated by inhibitory cytokines, particularly TGF-β1. To examine the roles of TGF-β1 and other inhibitory cytokines in the induction of oral tolerance, TGF-β1 null mice and controls were gavaged with 10 to 20 mg (high dose) or 1 mg (low dose) of OVA for 3 days. After immunization with OVA, the in vitro proliferative response of OVA-specific popliteal lymph node cells was assessed. Lymphocytes from all TGF-β1 null mice fed high doses of OVA exhibited highly significant suppression compared with controls. A weaker, but still significant, suppression was observed in lymphocytes from the majority of TGF-β1 null mice fed low doses of OVA. In addition, supernatants from these lymphocytes exhibited lower levels of IL-4, IL-10, and IFN-γ than those from water-fed control animals. These results indicate that while TGF-β1 may play a role in suppression, inhibitory cytokines are not the exclusive mechanism by ...
International Journal of Molecular Sciences, 2021
Background: Concerns are emerging that a high-fat diet rich in n-6 PUFA (n-6HFD) may alter gut mi... more Background: Concerns are emerging that a high-fat diet rich in n-6 PUFA (n-6HFD) may alter gut microbiome and increase the risk of intestinal disorders. Research is needed to model the relationships between consumption of an n-6HFD starting at weaning and development of gut dysbiosis and colonic inflammation in adulthood. We used a C57BL/6J mouse model to compare the effects of exposure to a typical American Western diet (WD) providing 58.4%, 27.8%, and 13.7% energy (%E) from carbohydrates, fat, and protein, respectively, with those of an isocaloric and isoproteic soybean oil-rich n-6HFD providing 50%E and 35.9%E from total fat and carbohydrates, respectively on gut inflammation and microbiome profile. Methods: At weaning, male offspring were assigned to either the WD or n-6HFD through 10–16 weeks of age. The WD included fat exclusively from palm oil whereas the n-6HFD contained fat exclusively from soybean oil. We recorded changes in body weight, cyclooxygenase-2 (COX-2) expression...
Development, 2002
The development of endochondral bones requires the coordination of signals from several cell type... more The development of endochondral bones requires the coordination of signals from several cell types within the cartilage rudiment. A signaling cascade involving Indian hedgehog (Ihh) and parathyroid hormone related peptide (PTHrP) has been described in which hypertrophic differentiation is limited by a signal secreted from chondrocytes as they become committed to hypertrophy. In this negative-feedback loop, Ihh inhibits hypertrophic differentiation by regulating the expression of Pthrp, which in turn acts directly on chondrocytes in the growth plate that express the PTH/PTHrP receptor. Previously, we have shown that PTHrP also acts downstream of transforming growth factor β (TGFβ) in a common signaling cascade to regulate hypertrophic differentiation in embryonic mouse metatarsal organ cultures. As members of the TGFβ superfamily have been shown to mediate the effects of Hedgehog in several developmental systems, we proposed a model where TGFβ acts downstream of Ihh and upstream of P...
Physiological reports, 2013
Pathological cardiac hypertrophy and cardiac fibrosis are remodeling events that result in mechan... more Pathological cardiac hypertrophy and cardiac fibrosis are remodeling events that result in mechanical stiffness and pathophysiological changes of the myocardium. Both humans and animal models display a sexual dimorphism where females are more protected from pathological remodeling. Fibroblast growth factor 2 (FGF2) mediates cardiac hypertrophy, cardiac fibrosis and protection against cardiac injury and is made in high molecular weight and low molecular weight isoforms (Hi FGF2 and Lo FGF2, respectively). Although some light has been shed on isoform-specific functions in cardiac pathophysiology, their roles in pathologic cardiac remodeling have yet to be determined. We tested the hypothesis that Lo FGF2 and Hi FGF2 modulate pathological cardiac remodeling in an isoform-specific manner. Young adult male and female mice between 8-12 weeks of age of mixed background that were deficient in either Hi FGF2 or Lo FGF2 (Hi KO or Lo KO, respectively) were subjected to daily injections of isop...
TheScientificWorldJournal, Jan 28, 2011
Recent studies have suggested an important role for periostin and transforming growth factor beta... more Recent studies have suggested an important role for periostin and transforming growth factor beta (TGF beta) and bone morphogenetic protein (BMP) ligands in heart valve formation and valvular heart diseases. The function of these molecules in cardiovascular development has previously been individually reviewed, but their association has not been thoroughly examined. Here, we summarize the current understanding of the association between periostin and TGF beta and BMP ligands, and discuss the implications of this association in the context of the role of these molecules in heart valve development and valvular homeostasis. Information about hierarchal connections between periostin and TGF beta and BMP ligands in valvulogenesis will increase our understanding of the pathogenesis, progression, and medical treatment of human valve diseases.
Cancer research, Jan 15, 2002
Patients with ulcerative colitis are at risk for colon cancer and frequently have microsatellite ... more Patients with ulcerative colitis are at risk for colon cancer and frequently have microsatellite instability,which, in turn, is usually associated with inactivation of transforming growth factor (TGF) beta signaling. TGF-beta1 deficiency in mice can lead to colon cancer that is preceded by precancerous lesions having submucosal inflammation and hyperplastic crypts. Germ-free TGF-beta1-deficient mice are free of inflammation, hyperplasia, and cancer, but when reintroduced into a Helicobacter hepaticus-containing specific pathogen-free room, these lesions reappear. Because adenoma/carcinoma but not inflammation/hyperplasia is dependent on the genetic backgrounds tested, colitis is required, but not sufficient, for carcinogenesis. This animal model should provide insight into the protective role of TGF-beta1 in early stages of ulcerative colitis-associated human colon cancer.
Cancer research, Jan 15, 1999
The transforming growth factor beta (TGF-beta) pathway is known to play an important role in both... more The transforming growth factor beta (TGF-beta) pathway is known to play an important role in both human and urine colon cancer. However, the staging, ligand specificity, and mechanism underlying the tumor suppressive activity of this pathway are unknown. We developed a mouse model for colon cancer that identifies an early role for TGF-beta1 in tumor suppression and implicates TGF-beta2 or TGF-beta3 in the prevention of metastasis. Analysis of the development of colon cancer in TGF-beta1 knockout mice pinpoints the defect to the hyperplasty/adenoma transition and reveals that the mechanism involves an inability to maintain epithelial tissue organization and not a loss of growth control, increased inflammatory activity, or increased genetic instability. These mice provide a unique opportunity to investigate the specific role of TGF-beta1 at this critical transition in the development of colon cancer.
The transforming growth factor b (TGF-b) pathway is known to play an important role in both human... more The transforming growth factor b (TGF-b) pathway is known to play an important role in both human and murine colon cancer. However, the staging, ligand specificity, and mechanism underlying the tumor suppres- sive activity of this pathway are unknown. We developed a mouse model for colon cancer that identifies an early role for TGF-b1 in tumor sup- pression and implicates
Development (Cambridge, England), 2002
The development of endochondral bones requires the coordination of signals from several cell type... more The development of endochondral bones requires the coordination of signals from several cell types within the cartilage rudiment. A signaling cascade involving Indian hedgehog (Ihh) and parathyroid hormone related peptide (PTHrP) has been described in which hypertrophic differentiation is limited by a signal secreted from chondrocytes as they become committed to hypertrophy. In this negative-feedback loop, Ihh inhibits hypertrophic differentiation by regulating the expression of Pthrp, which in turn acts directly on chondrocytes in the growth plate that express the PTH/PTHrP receptor. Previously, we have shown that PTHrP also acts downstream of transforming growth factor beta (TGFbeta) in a common signaling cascade to regulate hypertrophic differentiation in embryonic mouse metatarsal organ cultures. As members of the TGFbeta superfamily have been shown to mediate the effects of Hedgehog in several developmental systems, we proposed a model where TGFbeta acts downstream of Ihh and u...
The FASEB Journal, 2009
Genetic background significantly affects angiogenesis in mice. However, lymphangiogenic response ... more Genetic background significantly affects angiogenesis in mice. However, lymphangiogenic response to growth factors (GFs) in different strains has not been studied. We report constitutive expression of corneal lymphatics that extends beyond the limits of normal limbal vessels. In untreated corneas, the total number (P,)600.0؍ the number above blood vessels (P01؍ ؊8), and the area of preexisting lymphatics (P)700.0؍ were significantly higher in C57BL/6 than in BALB/c mice. Normal corneas of three other strains, the nu/nu, 129E, and Black Swiss mice, showed in most parameters intermediate phenotypes. FGF-2 Ϫ/Ϫ mice showed significantly less preexisting lymphatics than control (P,)900.0؍ which suggests a role for this GF in lymphatic development. VEGF-A-induced corneal lymphangiogenic response was significantly higher in BALB/c mice (P,)30.0؍ but it did not differ significantly in C57BL/6 mice, when compared to PBS-implanted control. FGFR-3 expression was higher in C57BL/6 than BALB/c mice, which suggests GFreceptor heterogeneity as a possible explanation for strain-dependent differences. The heterogeneity of preexisting lymphatic vessels in the limbal area significantly correlated with the extent of corneal lymphangiogenesis (VEGF-A: r,7.0؍ P;10.0؍ FGF-2: r,69.0؍ P01؍ ؊5) in BALB/c but not in C57BL/6 mice. Removal of conjunctival lymphatics did not affect GF-induced lymphangiogenesis. This work introduces physiological expression of lymphatics without blood vessels, which indicates that angiogenesis and lymphangiogenesis, even though intricately related, may occur independently. Furthermore, we show strain-dependence of normal and GF-induced lymphangiogenesis. These differences may affect disease development in various strains.
Nature Medicine, 1998
Vascular tone control is essential in blood pressure regulation, shock, ischemia-reperfusion, inf... more Vascular tone control is essential in blood pressure regulation, shock, ischemia-reperfusion, inflammation, vessel injury/repair, wound healing, temperature regulation, digestion, exercise physiology, and metabolism. Here we show that a well-known growth factor, FGF2, long thought to be involved in many developmental and homeostatic processes, including growth of the tissue layers of vessel walls, functions in vascular tone control. Fgf2 knockout mice are morphologically normal and display decreased vascular smooth muscle contractility, low blood pressure and thrombocytosis. Following intra-arterial mechanical injury, FGF2-deficient vessels undergo a normal hyperplastic response. These results force us to reconsider the function of FGF2 in vascular development and homeostasis in terms of vascular tone control.
Nature Genetics, 1995
Mice lacking TGF-β3 exhibit an incompletely penetrant failure of the palatal shelves to fuse lead... more Mice lacking TGF-β3 exhibit an incompletely penetrant failure of the palatal shelves to fuse leading to cleft palate. The defect appears to result from impaired adhesion of the apposing medial edge epithelia of the palatal shelves and subsequent elimination of the mid-line epithelial seam. No craniofacial abnormalities were observed. This result demonstrates that TGF-β3 affects palatal shelf fusion by an intrinsic, primary mechanism rather than by effects secondary to craniofacial defects. Members of the transforming growth factor-β (TGF-β) gene family have biological activities that control cell proliferation, migration and differentiation, regulation of extracellular matrix deposition and epithelial-mesenchymal transformation 1-3. Mammals contain three highly conserved isoforms of TGF-β, termed TGF-β1, TGF-β2 and TGF-β3, which display distinctive, although at times overlapping, spatial and temporal expression patterns 4-6. Previous studies suggested that TGF-β3 may play a crucial role during palatogenesis 7-9 , Meckel's cartilage formation 10 , cardiac morphogenesis 11 , mammary gland development 12 and wound healing 13. Other tissues expressing TGF-β3 in significant levels are cartilage, bone, brain and lung 4-6,14. In mammalian palatogenesis apposition of the palatal shelves, adhesion of the medial edge epithelia (MEE) and subsequent elimination of the epithelial seam lead to a seamless mesenchymal shelf separating the oral and nasal cavities 15. In vitro organ culture studies indicate that TGF-β1 and TGF-β2 accelerate palatal shelf fusion 16,17 and that antisense oligodeoxynucleotides or neutralizing antibodies to TGF-β3, but not to TGF-β1 or TGF-β2, block the fusion process 9. We have now created mice deficient in TGF-β3, and show that this factor has a role in palatal shelf fusion by means of an intrinsic, primary mechanism and not by effects secondary to craniofacial morphometrics. A comparison of this defect to the inflammatory disorder of TGF-β1-deficient mice 18-21 indicates no overlap in their essential functions.
Nature, 1992
Transforming growth factor-β1 (TGF-β1) is a multifunctional growth factor that has profound regul... more Transforming growth factor-β1 (TGF-β1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-β1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-β1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-β1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions. Transforming growth factor-β1 is the prototypic member of a family of structurally related polypeptides referred to as the transforming growth factor superfamily. Members of this family exhibit a variety of proliferative, inductive and regulatory properties, and include the TGF-βs, activins, inhibins, bone morphogenetic proteins, mullerian inhibiting substance, Drosophila decapentaplegic gene complex, and Xenopus Vg-l gene 1-3 TGF-β1 is synthesized as a precursor polypeptide containing a hydrophobic signal sequence, pro-region and mature peptide. The biologically active growth factor is a disulphide-linked homodimer, with each monomer representing the carboxy-terminal 112 amino acids of the precursor which are cleaved from the amino-terminal glycopeptide at a tetrabasic cleavage site 1-3. Three TGF-β isoforms, termed TGF-β1, TGF-β2 and TGF-β3, have been identified in mammals. These isoforms exhibit both overlapping and distinct spatial and temporal patterns of expression throughout development. Pronounced embryonic expression of the TGF-βs in areas undergoing morphogenetic events, particularly those involving epithelialmesenchymal interactions, suggests that these molecules playa critical role during embryonic development 4,5. The large number of cells and tissues that express embryonic TGF-β1 messenger RNA or protein are described in refs 6-11. In the adult, TGF-β1 immunoreactivity is detected in many cell types 12. TGF-β1 elicits diverse cellular responses depending on cell type, state of differentiation and culture conditions 1-3 Thus, TGF-β1 can have either stimulatory or inhibitory effects on the same cell, depending on the cellular environment 1-3. Biological actions of TGF-β1 include regulation of cell proliferation, control of extracellular matrix protein production and degradation, and modulation of cellular differentiation 1-3. In vitro studies with TGF-β1 have demonstrated inhibition of adipogenesis and myogenesis, inhibition of haematopoietic
Journal of Molecular and Cellular Cardiology, 2010
Fibroblast growth factor 2 (FGF2) consists of multiple protein isoforms (low [LMW] and high molec... more Fibroblast growth factor 2 (FGF2) consists of multiple protein isoforms (low [LMW] and high molecular weight [HMW]), which are localized to different cellular compartments, indicating unique biological activity. We previously showed that the LMW isoform is important in protecting the heart from myocardial dysfunction associated with ischemia-reperfusion (I/R) injury, but the roles of the HMW isoforms remain unknown. To elucidate the role of HMW isoforms in I/R and cardioprotection, hearts from novel mouse models,in which the murine FGF2 HMWs are knocked out (HMWKO) or the human FGF2 24 kDa HMW isoform is overexpressed (HMW Tg) and their wildtype (Wt) or non-transgenic (NTg) cohorts were subjected to an ex vivo work-performing heart model of I/R. There was a significant improvement in post-ischemic recovery of cardiac function in HMWKO hearts (76±5%, p<0.05) compared to Wt hearts (55±5%), with a corresponding decrease in HMW Tg function (line 20: 38±6% and line 28: 33±4%, p<0.05) compared to non-transgenic hearts (68±9%). FGF2 LMW isoform was secreted from Wt and HMWKO hearts during I/R, and a FGF receptor (FGFR) inhibitor, PD173074 caused a decrease in cardiac function when administered in I/R in Wt and FGF2 HMWKO hearts (p<0.05), indicating that FGFR is involved in FGF2 LMW isoform's biological effect in ischemia-reperfusion injury. Moreover, overexpression of HMW isoform reduced FGFR1 phosphorylation/activation with no further decrease in the phosphorylation state in the presence of the FGFR inhibitor. Overall, our data indicate that HMW isoforms have a detrimental role in the development of post-ischemic myocardial dysfunction.
Journal of Molecular and Cellular Cardiology, 2007
BACKGROUND: Our laboratory showed that overexpression of fibroblast growth factor-2 (FGF2) protec... more BACKGROUND: Our laboratory showed that overexpression of fibroblast growth factor-2 (FGF2) protected the heart against ischemia-reperfusion injury. FGF2 has different protein isoforms (low [LMW] and high [HMW] molecular weight isoforms) produced from alternative translation start sites. However, which FGF2 isoform(s) mediates this cardioprotection, and which signaling pathway (i.e., mitogen-activated protein kinase (MAPK)) elicits FGF2 isoform-induced cardioprotection remains to be elucidated. METHODS AND RESULTS: Wildtype, Fgf2 KO (absence of all FGF2 isoforms) and FGF2 LMWKO (absence of LMW isoform) hearts were subjected to an ex vivo work-performing heart ischemic model of 60 minutes ischemia and 120 minutes reperfusion. There was a significant decrease in the recovery of post-ischemic contractile function as well as in creatine kinase (CK) release (p<0.05) in Fgf2 KO and FGF2 LMWKO mouse hearts compared to wildtype hearts. Following ischemia-reperfusion injury, MKK4/7, JNK, and c-Jun were significantly phosphorylated (i.e., activated), and the levels of TUNEL-positive nuclei and caspase 3 cleavage were significantly increased in vehicle-treated Fgf2 KO and FGF2 LMWKO compared to wildtype hearts (p<0.05). A novel JNK pathway inhibitor, CEP11004 (50nM), significantly restored the post-ischemic contractile function and reduced myocardial cell death, as measured by CK release and apoptotic markers, compared to DMSO-treated cohorts (p<0.05). Overall, our data indicate that the LMW isoform has an important role in restoring cardiac function after ischemia-reperfusion (I/R) injury. These results provide unequivocal evidence that inhibition of JNK signaling is involved in FGF2 LMW isoformmediated cardioprotection and that the potential mechanism may be through inhibition of the apoptotic process.
Journal of Clinical Investigation, 1999
In vitro, fibroblast growth factor-2 (FGF2) has been implicated in cardiomyocyte growth and reexp... more In vitro, fibroblast growth factor-2 (FGF2) has been implicated in cardiomyocyte growth and reexpression of fetal contractile genes, both markers of hypertrophy. However, its in vivo role in cardiac hypertrophy during pressure overload is not well characterized. Mice with or without FGF2 (Fgf2 +/+ and Fgf2-/-, respectively) were subjected to transverse aortic coarctation (AC). Left ventricular (LV) mass and wall thickness were assessed by echocardiography preoperatively and once a week postoperatively for 10 weeks. In vivo LV function during dobutamine stimulation, cardiomyocyte cross-sectional area, and recapitulation of fetal cardiac genes were also measured. AC Fgf2-/mice develop significantly less hypertrophy (4-24% increase) compared with AC Fgf2 +/+ mice (41-52% increase). Cardiomyocyte cross-sectional area is significantly reduced in AC Fgf2-/mice. Noncoarcted (NC) and AC Fgf2-/mice have similar β-adrenergic responses, but those of AC Fgf2 +/+ mice are blunted. A lack of mitotic growth in both AC Fgf2 +/+ and Fgf2-/hearts indicates a hypertrophic response of cardiomyocytes. Consequently, FGF2 plays a major role in cardiac hypertrophy. Comparison of αand β-cardiac myosin heavy chain mRNA and protein levels in NC and AC Fgf2 +/+ and Fgf2-/mice indicates that myosin heavy chain composition depends on hemodynamic stress rather than on FGF2 or hypertrophy, and that isoform switching is transcriptionally, not posttranscriptionally, regulated.
Journal of Clinical Investigation, 2002
Angiotensin II (Ang II), a potent hypertrophic stimulus, causes significant increases in TGFb1 ge... more Angiotensin II (Ang II), a potent hypertrophic stimulus, causes significant increases in TGFb1 gene expression. However, it is not known whether there is a causal relationship between increased levels of TGF-β1 and cardiac hypertrophy. Echocardiographic analysis revealed that TGF-β1-deficient mice subjected to chronic subpressor doses of Ang II had no significant change in left ventricular (LV) mass and percent fractional shortening during Ang II treatment. In contrast, Ang II-treated wildtype mice showed a >20% increase in LV mass and impaired cardiac function. Cardiomyocyte crosssectional area was also markedly increased in Ang II-treated wild-type mice but unchanged in Ang II-treated TGF-β1-deficient mice. No significant levels of fibrosis, mitotic growth, or cytokine infiltration were detected in Ang II-treated mice. Atrial natriuretic factor expression was ∼6-fold elevated in Ang II-treated wild-type, but not TGF-β1-deficient mice. However, the αto β-myosin heavy chain switch did not occur in Ang II-treated mice, indicating that isoform switching is not obligatorily coupled with hypertrophy or TGF-β1. The Ang II effect on hypertrophy was shown not to result from stimulation of the endogenous renin-angiotensis system. These results indicate that TGF-β1 is an important mediator of the hypertrophic growth response of the heart to Ang II.
Journal of Cellular Physiology, 2009
Parathyroid hormone (PTH) increases Fibroblast growth factor receptor-1 (FGFR1) and Fibroblast gr... more Parathyroid hormone (PTH) increases Fibroblast growth factor receptor-1 (FGFR1) and Fibroblast growth factor-2 (FGF-2) expression in osteoblasts and the anabolic response to PTH is reduced in Fgf2−/− mice. This study examined whether candidate factors implicated in the anabolic response to PTH were modulated in Fgf2−/− osteoblasts. PTH increased Runx-2 protein expression in Fgf2+/+ but not Fgf2−/− osteoblasts. By immunocytochemistry, PTH treatment induced nuclear accumulation of Runx-2 only in Fgf2+/+ osteoblasts. PTH and FGF-2 regulate Runx-2 via activation of the cAMP response element binding proteins (CREBs). Western blot time course studies showed that PTH increased phospho-CREB within 15 min that was sustained for 24 h in Fgf2+/+ but had no effect in Fgf2−/− osteoblasts. Silencing of FGF-2 in Fgf2+/+ osteoblasts blocked the stimulatory effect of PTH on Runx-2 and CREBs phosphorylation. Studies of the effects of PTH on proteins involved in osteoblast precursor proliferation and apoptosis showed that PTH increased cyclinD1-cdk4/6 protein in Fgf2+/+ but not Fgf2−/− osteoblasts. Interestingly, PTH increased the cell cycle inhibitor p21/waf1 in Fgf2−/− osteoblasts. PTH increased Bcl-2/Bax protein ratio in Fgf2+/+ but not Fgf2−/− osteoblasts. In addition PTH increased cell viability in Fgf2+/+ but not Fgf2−/− osteoblasts. These data suggest that endogenous FGF-2 is important in PTH effects on osteoblast proliferation, differentiation and apoptosis. Reduced expression of these factors may contribute to the reduced anabolic response to PTH in the Fgf2−/− mice. Our results strongly indicate that the anabolic PTH effect is dependent in part on FGF-2 expression.
Journal of Biological Chemistry, 1999
Upon activation, platelets store and release large amounts of the peptide transforming growth fac... more Upon activation, platelets store and release large amounts of the peptide transforming growth factor 1 (TGF1). The released TGF1 can then act on nearby vascular cells to mediate subsequent vessel repair. In addition, TGF1 may circulate to bone marrow and regulate megakaryocyte activity. It is not known what effect, if any, TGF1 has on platelets. Adult TGF1-deficient mice exhibit thrombocythemia and a mild bleeding disorder that is shown to result from faulty platelet aggregation. TGF1-deficient platelets are shown to contain functional receptors, and preincubation with recombinant TGF1 improves aggregation, demonstrating that TGF1 plays an active role in platelet aggregation. TGF1-deficient platelets fail to retain bound fibrinogen in response to aggregation agonists, but they possess normal levels of the ␣ IIb / 3 fibrinogen receptor. Signaling from agonist receptors is normal because the platelets change shape, produce thromboxane A 2 , and present P-selectin in response to stimulation. Consequently, activation and maintenance of ␣ IIb / 3 into a fibrinogen-binding conformation is impaired in the absence of TGF1. 4-Phorbol 12-myristate 13-acetate treatment and protein kinase C activity measurements suggest a defect downstream of protein kinase C in its activation cascade. Because platelets lack nuclei, these data demonstrate for the first time a non-transcriptionally mediated TGF1 signaling pathway that enhances the activation and maintenance of integrin function.
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Papers by Thomas Doetschman