Faculty Bibliography

The glucuronide transporter GusB, the product of the gusB gene from Escherichia coli, is responsible for detoxification of metabolites. In this study, we successfully expressed GusB homologously in E. coli and investigated its oligomeric state in n-dodecyl-beta-D: -maltoside (DDM) detergent solution. Evidence for a pentameric state with a Stokes radius of 57 +/- 2 A for the purified GusB protein in DDM solution was obtained by analytical size-exclusion HPLC. The elution peak corresponding to pentameric GusB is commonly seen in elution profiles in the different buffer systems examined over a wide pH range. Hence, it is likely that GusB resides in the membrane as a pentamer. Stability studies with different incubation periods with the typical lipids, such as dimyristoylphosphatidylcholine, and total E. coli phospholipids, as the representatives of both phosphatidylcholine and phosphatidylethanolamine, show some clues to two-dimensional crystallization of GusB with lipids.

The mammary gland is an epidermal appendage that begins to form during embryogenesis, but whose development is only completed during pregnancy. Each mammary gland begins as a budlike invagination of the surface ectoderm, which then gives rise to a simple duct system by birth. Subsequent development occurs during sexual maturation and during pregnancy and lactation. In this review, we outline the distinct stages of embryonic mammary development and discuss the molecular pathways involved in the regulation of morphogenesis at each stage. We also discuss the potential relevance of embryonic breast development to the pathophysiology of breast cancer and highlight questions for future research

Understanding liver development should lead to greater insights into liver diseases and improve therapeutic strategies. In a forward genetic screen for genes regulating liver development in zebrafish, we identified a mutant--oliver--that exhibits liver-specific defects. In oliver mutants, the liver is specified, bile ducts form and hepatocytes differentiate. However, the hepatocytes die shortly after their differentiation, and thus the resulting mutant liver consists mainly of biliary tissue. We identified a mutation in the gene encoding translocase of the outer mitochondrial membrane 22 (Tomm22) as responsible for this phenotype. Mutations in tomm genes have been associated with mitochondrial dysfunction, but most studies on the effect of defective mitochondrial protein translocation have been carried out in cultured cells or unicellular organisms. Therefore, the tomm22 mutant represents an important vertebrate genetic model to study mitochondrial biology and hepatic mitochondrial diseases. We further found that the temporary knockdown of Tomm22 levels by morpholino antisense oligonucleotides causes a specific hepatocyte degeneration phenotype that is reversible: new hepatocytes repopulate the liver as Tomm22 recovers to wild-type levels. The specificity and reversibility of hepatocyte ablation after temporary knockdown of Tomm22 provides an additional model to study liver regeneration, under conditions where most hepatocytes have died. We used this regeneration model to analyze the signaling commonalities between hepatocyte development and regeneration.

BACKGROUND & AIMS: Nonalcoholic steatohepatitis (NASH) is a disorder that consists of steatosis and hepatic inflammation. It is not known why only some people with steatosis develop NASH. Recently, we identified dietary cholesterol as a factor that directly leads to hepatic inflammation and hepatic foam cell formation. We propose a mechanism by which Kupffer cells (KCs) take up modified cholesterol-rich lipoproteins via scavenger receptors (SRs). KCs thereby accumulate cholesterol, become activated, and may then trigger an inflammatory reaction. Scavenging of modified lipoproteins mainly depends on CD36 and macrophage scavenger receptor 1. METHODS: To evaluate the involvement of SR-mediated uptake of modified lipoproteins by KCs in the development of diet-induced NASH, female low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice were lethally irradiated and transplanted with bone marrow from Msr1(+/+)/Cd36(+/+)or Msr1(-/-)/Cd36(-/-) mice and fed a Western diet. RESULTS: Macrophage and neutrophil infiltration revealed that hepatic inflammation was substantially reduced by approximately 30% in Msr1(-/-)/Cd36(-/-)-transplanted mice compared with control mice. Consistent with this, the expression levels of well-known inflammatory mediators were reduced. Apoptotis and fibrosis were less pronounced in Msr1(-/-)/Cd36(-/-)-transplanted mice, in addition to the protective phenotype of natural antibodies against oxidized low-density lipoprotein in the plasma. Surprisingly, the effect on hepatic inflammation was independent of foam cell formation. CONCLUSIONS: Targeted inactivation of SR pathways reduces the hepatic inflammation and tissue destruction associated with NASH, independent of hepatic foam cell formation

High density lipoprotein (HDL), an endogenous nanoparticle, transports fat throughout the body and is capable of transferring cholesterol from atheroma in the vessel wall to the liver. In the present study, we utilized HDL as a multimodal nanoparticle platform for tumor targeting and imaging via nonspecific accumulation and specific binding to angiogenically activated blood vessels. We reconstituted HDL (rHDL) with amphiphilic gadolinium chelates and fluorescent dyes. To target angiogenic endothelial cells, rHDL was functionalized with alphavbeta3-integrin-specific RGD peptides (rHDL-RGD). Nonspecific RAD peptides were conjugated to rHDL nanoparticles as a control (rHDL-RAD). It was observed in vitro that all 3 nanoparticles were phagocytosed by macrophages, while alphavbeta3-integrin-specific rHDL-RGD nanoparticles were preferentially taken up by endothelial cells. The uptake of nanoparticles in mouse tumors was evaluated in vivo using near infrared (NIR) and MR imaging. All nanoparticles accumulated in tumors but with very different accumulation/binding kinetics as observed by NIR imaging. Moreover, confocal microscopy revealed rHDL-RGD to be associated with tumor endothelial cells, while rHDL and rHDL-RAD nanoparticles were mainly found in the interstitial space. This study demonstrates the ability to reroute HDL from its natural targets to tumor blood vessels and its potential for multimodal imaging of tumor-associated processes.

Bone morphogenetic proteins (BMPs) participate in multiple stages of the fetal skeletogenic program from promoting cell condensation to regulating chondrogenesis and bone formation through endochondral ossification. Here, we show that these pleiotropic functions are recapitulated when recombinant BMPs are used to augment skeletal tissue repair. In addition to their well-documented ability to stimulate chondrogenesis in a skeletal injury, we show that recombinant BMPs (rBMPs) simultaneously suppress the differentiation of skeletal progenitor cells in the endosteum and bone marrow cavity to an osteoblast lineage. Both the prochondrogenic and antiosteogenic effects are achieved because rBMP inhibits endogenous beta-catenin-dependent Wnt signaling. In the injured periosteum, this repression of Wnt activity results in sox9 upregulation; consequently, cells in the injured periosteum adopt a chondrogenic fate. In the injured endosteum, rBMP also inhibits Wnt signaling, which results in the runx2 and collagen type I downregulation; consequently, cells in this region fail to differentiate into osteoblasts. In muscle surrounding the skeletal injury site, rBMP treatment induces Smad phosphorylation followed by exuberant cell proliferation, an increase in alkaline phosphatase activity, and chondrogenic differentiation. Thus different populations of adult skeletal progenitor cells interpret the same rBMP stimulus in unique ways, and these responses mirror the pleiotropic effects of BMPs during fetal skeletogenesis. These mechanistic insights may be particularly useful for optimizing the reparative potential of rBMPs while simultaneously minimizing their adverse outcomes.

Granulin epithelin precursor (GEP) has been implicated in development, tissue regeneration, tumorigenesis, and inflammation. Herein we report that GEP stimulates chondrocyte differentiation from mesenchymal stem cells in vitro and endochondral ossification ex vivo, and GEP-knockdown mice display skeleton defects. Similar to bone morphogenic protein (BMP) 2, application of the recombinant GEP accelerates rabbit cartilage repair in vivo. GEP is a key downstream molecule of BMP2, and it is required for BMP2-mediated chondrocyte differentiation. We also show that GEP activates chondrocyte differentiation through Erk1/2 signaling and that JunB transcription factor is one of key downstream molecules of GEP in chondrocyte differentiation. Collectively, these findings reveal a novel critical role of GEP growth factor in chondrocyte differentiation and the molecular events both in vivo and in vitro.

Irradiation of an amorphous layer of dried sodium phosphate buffer (pH = 7.0) by transmission electron microscopy (100-120 kV) causes rapid formation of numerous small spherical bubbles [10-100 A (= 1-10 nm)] containing an unknown gas. Bubbling is detected even with the first low-dose exposure. In a thin layer (ca. 100-150 A), bubbling typically goes through nucleation, growth, possible fusion, and end-state, after which further changes are not apparent; co-irradiated adjacent areas having a slightly smaller thickness never develop bubbles. In moderately thicker regions (ca. over 200 A), there is no end-state. Instead, a complex sequence of microstructural changes is elicited during continued intermittent high-dose irradiation: nucleation, growth, early simple fusions, a second round of extensive multiple fusions, general reduction of matrix thickness (producing flattening and expansion of larger bubbles, occasional bubble fission, and formation of very large irregularly-shaped bubbles by a third round of compound fusion events), and slow shrinkage of all bubbles. The ongoing lighter appearance of bubble lumens, maintenance of their rounded shape, and extensive changes in size and form indicate that gas content continues throughout their surprisingly long lifetime; the thin dense boundary layer surrounding all bubbles is proposed to be the main mechanism for their long lifetime.

In Drosophila, germ cell survival and directionality of migration are controlled by two lipid phosphate phosphatases (LPP), wunen (wun) and wunen-2 (wun2). wun wun2 double mutant analysis reveals that the two genes, hereafter collectively called wunens, act redundantly in primordial germ cells. We find that wunens mediate germ cell-germ cell repulsion and that this repulsion is necessary for germ cell dispersal and proper transepithelial migration at the onset of migration and for the equal sorting of the germ cells between the two embryonic gonads during their migration. We propose that this dispersal function optimizes adult fecundity by assuring maximal germ cell occupancy of both gonads. Furthermore, we find that the requirement for wunens in germ cell survival can be eliminated by blocking germ cell migration. We suggest that this essential function of Wunen is needed to maintain cell integrity in actively migrating germ cells