Search

Type 1 alveolar epithelial cells (AT1s) and type 2 alveolar epithelial cells (AT2s) regulate the structural integrity and function of alveoli. AT1s mediate gas exchange, whereas AT2s serve multiple functions, including surfactant secretion and alveolar repair through proliferation and differentiation into AT1s as progenitors. However, mechanisms regulating AT2 proliferation and differentiation remain unclear. Here we demonstrate that Gremlin, an intrinsic inhibitor of bone morphogenetic protein (BMP), induces AT2 proliferation and differentiation. Transient overexpression of Gremlin in rat lungs by adenovirus vector delivery suppressed BMP signaling, induced proliferation of AT2s and the production of Bmp2, which in turn led to the recovery of BMP signaling and induced AT2 differentiation into AT1s. Bleomycin-induced lung injury upregulated Gremlin and showed a similar time course of biomarker expression comparable to the adenovirus model. TGF-β and IL-1β induced Gremlin expression in fibroblasts. Taken together, our findings implicate that Gremlin expression during lung injury leads to precisely timed inhibition of BMP signaling and activates AT2s, leading to alveolar repair. • Regulation mechanisms of type 2 alveolar epithelial cells (AT2) are unclear. • Gremlin, an intrinsic BMP inhibitor, leads to AT2 proliferation and differentiation. • Gremlin expression upregulated in lung injury, leading to AT2 activation. • TGF-beta and IL-1beta induce Gremlin expression in fibroblasts. • Findings implicate Gremlin as key player in lung injury repair. [ABSTRACT FROM AUTHOR]

The DAN gene family (DAN, Differential screening-selected gene Aberrant in Neuroblastoma) is a group of genes that is expressed during development and plays fundamental roles in limb bud formation and digitation, kidney formation and morphogenesis and left-right axis specification. During adulthood the expression of these genes are associated with diseases, including cancer. Although most of the attention to this group of genes has been dedicated to understanding its role in physiology and development, its evolutionary history remains poorly understood. Thus, the goal of this study is to investigate the evolutionary history of the DAN gene family in vertebrates, with the objective of complementing the already abundant physiological information with an evolutionary context. Our results recovered the monophyly of all DAN gene family members and divide them into five main groups. In addition to the well-known DAN genes, our phylogenetic results revealed the presence of two new DAN gene lineages; one is only retained in cephalochordates, whereas the other one (GREM3) was only identified in cartilaginous fish, holostean fish, and coelacanth. According to the phyletic distribution of the genes, the ancestor of gnathostomes possessed a repertoire of eight DAN genes, and during the radiation of the group GREM1, GREM2, SOST, SOSTDC1, and NBL1 were retained in all major groups, whereas, GREM3, CER1, and DAND5 were differentially lost. [Display omitted] • We recovered the monophyly of all DAN paralogs and divided them into five groups. • We described two new DAN gene lineages. • The ancestor of gnathostomes possessed a repertoire of eight DAN genes. [ABSTRACT FROM AUTHOR]

Mutations in the Bone Morphogenetic Protein (BMP) pathway are associated with a range of defects in skeletal formation. Genetic analysis of BMP signaling requirements is complicated by the presence of three partially redundant BMPs that are required for multiple stages of limb development. We generated an inducible allele of a BMP inhibitor, Gremlin , which reduces BMP signaling. We show that BMPs act in a dose and time dependent manner in which early reduction of BMPs result in digit loss, while inhibiting overall BMP signaling between E10.5 and E11.5 allows polydactylous digit formation. During this period, inhibiting BMPs extends the duration of FGF signaling. Sox9 is initially expressed in normal digit ray domains but at reduced levels that correlate with the reduction in BMP signaling. The persistence of elevated FGF signaling likely promotes cell proliferation and survival, inhibiting the activation of Sox9 and secondarily, inhibiting the differentiation of Sox9 -expressing chondrocytes. Our results provide new insights into the timing and clarify the mechanisms underlying BMP signaling during digit morphogenesis. [ABSTRACT FROM AUTHOR]

Highlights: [•] TGF-β2, CTGF and gremlin can induce HLECs expression of EMT and ECM. [•] Silencing gremlin and CTGF effectively block gremlin and CTGF-induced EMT and ECM. [•] TGF-β2, gremlin and CTGF can activate Smad signaling pathway in HLECs. [•] Silencing gremlin or CTGF effectively inhibit the TGF-β2/Smad signaling pathway. [•] Blockade of Smad2 and Smad3 can inhibit gremlin and CTGF-induced EMT and ECM. [ABSTRACT FROM AUTHOR]

Abstract: The TGFβ/BMP signaling pathways are involved in glaucomatous damage to the trabecular meshwork (TM) leading to elevated intraocular pressure (IOP), which is a major risk factor for the development and progression of glaucoma. The BMP antagonist gremlin is elevated in glaucomatous TM cells and tissues and can directly elevate IOP. Gremlin utilizes the TGFβ2/SMAD pathway to induce TM extracellular matrix (ECM) proteins. The purpose of this study is to determine whether expression of the ECM cross-linking lysyl oxidase (LOX) genes is regulated by gremlin in cultured human TM cells. Human TM cells were treated with recombinant gremlin, and expression of the LOX genes was examined by quantitative RT-PCR and western immunoblotting. TM cells were pretreated with TGFBR inhibitors (LY364947 or SB431542), an inhibitor of the SMAD signaling pathway (SIS3), or with JNK (SP600125) and p38 MAPK (SB203580) inhibitors to identify the signaling pathway(s) involved in gremlin induction of LOX protein expression. All five LOX genes (LOX and LOXL1–4) were induced by gremlin. Gremlin induction of LOX genes and protein expression was blocked by TGFBR inhibitors as well as by inhibitors of the SMAD3, JNK and p38 MAPK signaling pathways. We conclude that gremlin employs both canonical TGFβ/SMAD and the non-canonical JNK and p38 MAPK signaling pathways to induce LOX genes and proteins in cultured human TM cells. Increased LOX levels may be at least partially responsible for gremlin-mediated IOP elevation and increased aqueous humor outflow resistance leading to glaucoma. [Copyright &y& Elsevier]

Abstract: In patients with primary open angle glaucoma (POAG), the optic nerve head (ONH) shows characteristic cupping correlated with visual field defects. The progressive optic neuropathy is characterized by irreversible loss of retinal ganglion cells (RGC). The critical risk factor for axonal damage at the ONH is an elevated intraocular pressure (IOP). The increase in IOP correlates with axonal loss in the ONH, which might be due to an impaired axoplasmatic flow leading to the loss of RGCs. Damage to the optic nerve is thought to occur in the lamina cribrosa (LC) region of the ONH, which is composed of characteristic sieve-like connective tissue cribriform plates through which RGC axons exit the eye. The cupping of the optic disc, and the compression and excavation of LC are characteristic signs of glaucomatous ONH remodelling. In ONH of POAG patients a disorganized distribution and deposition of elastic fibers and a typical pronounced thickening of the connective tissue septae surrounding the optic nerve fibers is found. Transforming growth factor (TGF)-β2 could be one of the pathogenic factors responsible for the structural alterations in POAG patients as the TGF-β2 levels in the ONH of glaucomatous eyes are elevated as well as in the aqueous homour. TGF-β2 leads to an increased synthesis of extracellular matrix (ECM) molecules mediated by connective tissue growth factor and to an impaired ECM degradation in cultured ONH astrocytes. Bone morphogenetic protein (BMP)-4 effectively antagonizes the effects of TGF-β2 on matrix deposition. The BMP antagonist gremlin blocks this inhibition, allowing TGF-β2 stimulation of ECM synthesis. Overall, the ECM in the ONH is kept in balance in the OHN by factors that augment or block the activity of TGF-β2. [Copyright &y& Elsevier]

Abstract: We have studied hypertrophic and immediately adjacent pre-hypertrophic chondrocytes at the same stage of histologic development in 7day old post-natal Balb/C mouse physes and epiphyses. Laser capture microdissection (LCM) and GeneChip microarray analysis compared the molecular composition of the two hypertrophic chondrocyte regions. Molecules upregulated in dramatically higher levels in the epiphysis were gremlin (58-fold), epidermal growth factor-containing fibulin-like extracellular matrix protein 1 (25-fold), and frizzled related protein (6.4-fold and 5.7-fold). Molecules upregulated in higher levels in the physis were proline arginine-rich end leucine-rich repeat protein (PRELP) (15.6-fold), pyrophosphatase (inorganic) 1 (10-fold) and hedgehog-interacting protein (7.3-fold). Immunocytochemistry for gremlin confirmed specific localization patterns. This study indicates a critical site-specific role for hypertrophic chondrocytes with different synthesis patterns in separate regions even though they appear structurally the same and are at the same stage of development. [Copyright &y& Elsevier]

Abstract: Recent reports highlight the importance of BMP in the vasculature. We investigated the expression pattern and role of the BMP antagonist gremlin in VSMC. We detected gremlin mRNA constitutive expression in adult and embryonic rat aortic VSMC, and in rat carotids. In vitro analysis demonstrated that angiotensin II, TGF-β1 and PDGF induced significant changes in gremlin mRNA expression. Gremlin stable overexpression in A7r5 cells blocked BMP signaling. BMP-induced reduction in VSMC DNA synthesis was markedly inhibited by gremlin overexpression. In fact, gremlin overexpression increased DNA synthesis and cell counts, and accelerated cell cycle progression of VSMC, through mechanisms that include p27kip1 down-regulation. Gremlin also led to marked increments in VSMC migration. In addition, gremlin gene silencing promoted a significant blockade on cell proliferation and migration. In vivo studies disclosed increased gremlin protein expression in the neointima of balloon-injured carotid arteries. In summary, the BMP antagonist gremlin is constitutively expressed in the normal vasculature. Gremlin induces VSMC proliferation and migration and is significantly regulated by growth factors and injury. We postulate that gremlin plays a part in the development of pathological phenotypic changes of adult VSMC. [Copyright &y& Elsevier]

Abstract: Proper outgrowth of the limb bud requires a positive feedback loop between Sonic hedgehog (Shh) in the zone of polarizing activity (ZPA) and Fgfs in the overlying apical ectodermal ridge. The Bmp antagonist Gremlin is expressed in a domain anterior to the ZPA and is thought to act as a signaling intermediate between Shh and Fgf. It is currently unclear whether Shh acts directly or indirectly to initiate and maintain Gremlin. In this study, we confirm that Bmp activity is necessary and sufficient for induction of Gremlin. Beads soaked in the Bmp antagonist Noggin downregulate Gremlin, while beads soaked in Bmp2 cause its upregulation. Furthermore, Bmp2 is also capable of upregulating Gremlin in oligozeugodactyly mutant limbs that lack Shh activity, demonstrating that Gremlin expression does not depend on the combined exposure to both these factors. In spite of the ability of Bmp2 to induce Gremlin, beads soaked in high concentrations of Bmp2 downregulate Gremlin around the bead without apparent induction of cell death, whereas another target gene Msx2 is upregulated around the bead. Consistent with this concentration-dependent effect, we find that low concentrations of Bmp2 upregulate Gremlin while high concentrations of Bmp2 downregulate Gremlin in limb mesenchyme cultures. These data implicate Bmp activity as a required intermediate in the Shh–Fgf4 signaling loop. Though we show that Bmp activity is sufficient to upregulate Gremlin, Gremlin expression is excluded from a posterior domain of the limb, and expansion of this domain as limb outgrowth proceeds is important in terminating the Shh–Fgf4 signaling loop. We find that the posterior limb is refractory to Gremlin induction in response to Bmp2, suggesting that termination of the Shh–Fgf4 signaling loop results from inability of Bmp activity to induce Gremlin in the posterior. In contrast, in the oligozeugodactyly limb, we find that beads soaked in Bmp2 can induce Gremlin in the posterior, demonstrating that Shh activity is required for exclusion of Gremlin in the posterior. Finally, by blocking Shh activity with cyclopamine, we find evidence that continued Shh activity is also required to maintain refractoriness to Gremlin expression in response to Bmp activity. [Copyright &y& Elsevier]

Abstract: The evolutionary origin of the anterior–posterior and the dorsoventral body axes of Bilateria is a long-standing question. It is unclear how the main body axis of Cnidaria, the sister group to the Bilateria, is related to the two body axes of Bilateria. The conserved antagonism between two secreted factors, BMP2/4 (Dpp in Drosophila) and its antagonist Chordin (Short gastrulation in Drosophila) is a crucial component in the establishment of the dorsoventral body axis of Bilateria and could therefore provide important insight into the evolutionary origin of bilaterian axes. Here, we cloned and characterized two BMP ligands, dpp and GDF5-like as well as two secreted antagonists, chordin and gremlin, from the basal cnidarian Nematostella vectensis. Injection experiments in zebrafish show that the ventralizing activity of NvDpp mRNA is counteracted by NvGremlin and NvChordin, suggesting that Gremlin and Chordin proteins can function as endogenous antagonists of NvDpp. Expression analysis during embryonic and larval development of Nematostella reveals asymmetric expression of all four genes along both the oral–aboral body axis and along an axis perpendicular to this one, the directive axis. Unexpectedly, NvDpp and NvChordin show complex and overlapping expression on the same side of the embryo, whereas NvGDF5-like and NvGremlin are both expressed on the opposite side. Yet, the two pairs of ligands and antagonists only partially overlap, suggesting complex gradients of BMP activity along the directive axis but also along the oral–aboral axis. We conclude that a molecular interaction between BMP-like molecules and their secreted antagonists was already employed in the common ancestor of Cnidaria and Bilateria to create axial asymmetries, but that there is no simple relationship between the oral–aboral body axis of Nematostella and one particular body axis of Bilateria. [Copyright &y& Elsevier]

Abstract: Specific therapies of diabetic nephropathy (DN) are not available, and current treatment strategies are limited to management of blood glucose levels and control of hypertension. The re-activation of developmental programs in DN suggests new potential therapeutic targets. Bone morphogenetic protein-7 (BMP-7) and its antagonist, Gremlin is revealed to be involved in renal development and diabetic nephropathy. This article reviews the changes of BMP-7 and Gremlin in diabetic kidney, the protective effects on diabetic nephropathy when targeting BMP-7 and Gremlin, and the possible mechanism. The reorganization of the re-activation of Gremlin and BMP-7 in diabetic kidney had shed light on the identification of novel therapeutic targets for DN. [Copyright &y& Elsevier]