Enhanced Efficacy of Cholesterol-Minus Sonic Hedgehog in Postnatal Skin

Gestational iron deficiency affects the ratio between interneuron subtypes in the postnatal cerebral cortex in mice

Gestational iron deficiency (gID) is highly prevalent and associated with an increased risk of intellectual and developmental disabilities in affected individuals that are often defined by a disrupted balance of excitation and inhibition (E/I) in the brain. Using a nutritional mouse model of gID, we previously demonstrated a shift in the E/I balance towards increased inhibition in the brains of gID offspring that was refractory to postnatal iron supplementation. We thus tested whether gID affects embryonic progenitor cells that are fated towards inhibitory interneurons. We quantified relevant cell populations during embryonic inhibitory neuron specification and found an increase in the proliferation of Nkx2.1+ interneuron progenitors in the embryonic medial ganglionic eminence at E14 that was associated with increased Shh signaling in gID animals at E12. When we quantified the number of mature inhibitory interneurons that are known to originate from the MGE, we found a persistent disruption of differentiated interneuron subtypes in early adulthood. Our data identify a cellular target that links gID with a disruption of cortical interneurons which play a major role in the establishment of the E/I balance.

Hepatic expression of Sonic Hedgehog induces liver fibrosis and promotes hepatocarcinogenesis in a transgenic mouse model

BACKGROUND & AIMS

Liver fibrosis is an increasing health concern worldwide and a major risk factor for hepatocellular carcinoma (HCC). Although the involvement of Hedgehog signaling in hepatic fibrosis has been known for some time, the causative role of activated Hedgehog signaling in liver fibrosis has not been verified in vivo.

METHODS

Using hydrodynamics-based transfection, a transgenic mouse model has been developed that expresses Sonic Hedgehog (SHH), a ligand for Hedgehog signaling, in the liver. Levels of hepatic fibrosis and fibrosis-related gene expression were assessed in the model. Hepatic expression of SHH was induced in a murine model for hepatocellular adenoma (HCA) and tumor development was subsequently investigated.

RESULTS

The transgenic mice revealed SHH expression in 2-5% of hepatocytes. Secreted SHH activated Hedgehog signaling in numerous cells of various types in the tissues. Hepatic expression of SHH led to fibrosis, activation of hepatic stellate cells, and an upregulation of various fibrogenic genes. Liver injury and hepatocyte apoptosis were observed in SHH mice. Persistent expression of SHH for up to 13months failed to induce tumors in the liver; however, it promoted liver tumor development induced by other oncogenes. By employing a HCA model induced by P53(R172H) and KRAS(G12D), we found that the SHH expression promoted the transition from HCA to HCC.

CONCLUSIONS

SHH expression in the liver induces liver fibrosis with concurrent activation of hepatic stellate cells and fibrogenic genes. It can also enhance hepatocarcinogenesis induced by other oncogenes.

Overexpressing sonic hedgehog peptide restores periosteal bone formation in a murine bone allograft transplantation model

Although activation of hedgehog (Hh) signaling has been shown to induce osteogenic differentiation in vitro and bone formation in vivo, the underlying mechanisms and the potential use of Hh-activated mesenchymal progenitors in bone defect repair remain elusive. In this study, we demonstrated that implantation of periosteal-derived mesenchymal progenitor cells (PDMPCs) that overexpressed an N-terminal sonic hedgehog peptide (ShhN) via an adenoviral vector (Ad-ShhN) restored periosteal bone collar formation in a 4-mm segmental bone allograft model in immunodeficient mice. Ad-ShhN enhanced donor cell survival and microvessel formation in collagen scaffold at 2 weeks after surgery and induced donor cell-dependent bone formation at 6 weeks after surgery. Fluorescence-activated cell sorting analysis further showed that Ad-ShhN-PDMPC-seeded scaffold contained a twofold more CD45(-)Sca-1(+)CD34(+)VEGFR2(+) endothelial progenitors than Ad-LacZ-PDMPC-seeded scaffold at day 7 after surgery. Ad-ShhN-transduced PDMPCs induced a 1.8-fold more CD31(+) microvessel formation than Ad-LacZ-transduced PDMPCs in a coculture of endothelial progenitors and PDMPCs. Taken together, our data show that overexpression of ShhN in mesenchymal progenitors improves bone defect reconstruction by enhancing donor progenitor cell survival, differentiation, and scaffold revascularization at the site of compromised periosteum. Hh agonist-based therapy, therefore, merits further investigation in tissue engineering-based applications aimed at enhancing bone defect repair and reconstruction.

Activation of the Hh pathway in periosteum-derived mesenchymal stem cells induces bone formation in vivo: implication for postnatal bone repair

While the essential role of periosteum in cortical bone repair and regeneration is well established, the molecular pathways that control the early osteogenic and chondrogenic differentiation of periosteal stem/progenitor cells during repair processes are unclear. Using a murine segmental bone graft transplantation model, we isolated a population of early periosteum-callus-derived mesenchymal stem cells (PCDSCs) from the healing autograft periosteum. These cells express typical mesenchymal stem cell markers and are capable of differentiating into osteoblasts, adipocytes, and chondrocytes. Characterization of these cells demonstrated that activation of the hedgehog (Hh) pathway effectively promoted osteogenic and chondrogenic differentiation of PCDSCs in vitro and induced bone formation in vivo. To determine the role of the Hh pathway in adult bone repair, we deleted Smoothened (Smo), the receptor that transduces all Hh signals at the onset of bone autograft repair via a tamoxifen-inducible RosaCreER mouse model. We found that deletion of Smo markedly reduced osteogenic differentiation of isolated PCDSCs and further resulted in a near 50% reduction in periosteal bone callus formation at the cortical bone junction as determined by MicroCT and histomorphometric analyses. These data strongly suggest that the Hh pathway plays an important role in adult bone repair via enhancing differentiation of periosteal progenitors and that activation of the Hh pathway at the onset of healing could be beneficial for repair and regeneration.

Overexpression of sonic Hedgehog in the lung mimics the effect of lung injury and compensatory lung growth on pulmonary Sca-1 and CD34 positive cells

Cells localized in the bronchioalveolar duct junction of the murine lung have been identified as potential bronchioalveolar stem cells. Based on the surface marker expression, two main phenotypes have been proposed: Sca-1(+), CD34(+), CD45(-), Pecam(-) and Sca-1(low), CD34(-) CD45(-), Pecam(-) cells. An increase in the number of Sca-1(+), CD34(+) CD45(-), Pecam(-) cells and activation of the sonic hedgehog (Shh) pathway was observed following unilateral pneumonectomy and naphthalene-induced airway injury. Overexpression of Shh in the respiratory tract also resulted in an increase of this cell population. Syngeneic transplantation of beta-galactosidase-expressing bone marrow cells demonstrated that the increase of Sca-1(+), CD34(+), CD45(-), Pecam(-) cells in the lung was a result of local proliferation. Intratracheal administration of purified Shh-stimulated Sca-1(+), CD45(-), Pecam(-) cells coexpressing CD34 to syngeneic mice following pneumonectomy resulted in engraftment of these cells predominantly in the airways for up to 3 months, whereas Sca-1(-), CD45(-), Pecam(-) cells did not engraft. This study suggests that local Sca-1(+), CD34(+), CD45(-), Pecam(-) cells are stimulated during compensatory lung growth, following airway injury and overexpression of Shh and have some potential to engraft in the airways, without showing clonal properties in vivo.

Transient overexpression of sonic hedgehog alters the architecture and mechanical properties of trabecular bone

Bone formation and remodeling involve coordinated interactions between osteoblasts and osteoclasts through signaling networks involving a variety of molecular pathways. We hypothesized that overexpression of Sonic hedgehog (Shh), a morphogen with a crucial role in skeletal development, would stimulate osteoblastogenesis and bone formation in adult animals in vivo. Systemic administration of adenovirus expressing the N-terminal form of Shh into adult mice resulted in a primary increase in osteoblasts and their precursors. Surprisingly, however, this was associated with altered trabecular morphology, decreased bone volume, and decreased compressive strength in the vertebrae. Whereas no change was detected in the number of osteoclast precursors, bone marrow stromal cells from Shh-treated mice showed enhanced osteoclastogenic potential in vitro. These effects were mediated by the PTH/PTH-related protein (PTHrP) pathway as evidenced by increased sensitivity to PTH stimulation and upregulation of the PTH/PTHrP receptor (PPR). Together, these data show that Shh has stimulatory effects on osteoprogenitors and osteoblasts in adult animals in vivo, which results in bone remodeling and reduced bone strength because of a secondary increase in osteoclastogenesis.

Sonic hedgehog expands diaphyseal trabecular bone altering bone marrow niche and lymphocyte compartment

Bone marrow contains distinct microenvironments that regulate hematopoietic stem cells (HSCs). The endosteal HSC niche includes osteoblasts, mineral, and extracellular matrix proteins that interact through various molecular signals to control HSCs. Sonic hedgehog (Shh) is a morphogen involved in the regulation of skeletal development and hematopoiesis, but the effects of Shh on bone in relation to the HSC niche are not well understood. We demonstrate that systemic overexpression of Shh in mice increases osteoblast number with the resultant formation of new trabeculae in the femoral diaphysis. Suggestive of a functional change in the hematopoietic niche, numbers of Lin(-) Sca-1(+) c-Kit(+) cells with hematopoietic progenitor function expand, although cells with in vivo repopulating capacity in the wild-type environment do not increase. Instead, Shh mediates a decrease in number of bone marrow lymphocytes accompanied by a decreased expression of stromal-derived growth factor 1 (SDF-1) and a decrease in Flk2-expressing Lin(-) Sca-1(+) c-Kit(+) cells, indicating a modulation of early lymphopoiesis. This is caused by a microenvironment-induced mechanism as Shh treatment of bone marrow recipients, but not donors, results in a dramatic depletion of lymphocytes. Together, these data suggest that Shh mediates alterations in the bone marrow hematopoietic niche affecting the early lymphoid differentiation.