Andrew C. White

FGF9 and SHH signaling coordinate lung growth and development through regulation of distinct mesenchymal domains

Morphogenesis of the lung is regulated by reciprocal signaling between epithelium and mesenchyme. In previous studies, we have shown that FGF9 signals are essential for lung mesenchyme development. Using Fgf9 loss-of-function and inducible gain-of-function mouse models, we show that lung mesenchyme can be divided into two distinct regions: the sub-mesothelial and sub-epithelial compartments, which proliferate in response to unique growth factor signals. Fibroblast growth factor (FGF) 9 signals from the mesothelium (the future pleura) to sub-mesothelial mesenchyme through both FGF receptor (FGFR) 1 and FGFR2 to induce proliferation. FGF9 also signals from the epithelium to the sub-epithelial mesenchyme to maintain SHH signaling, which regulates cell proliferation, survival and the expression of mesenchymal to epithelial signals. We further show that FGF9 represses peribronchiolar smooth muscle differentiation and stimulates vascular development in vivo. We propose a model in which FGF9 and SHH signals cooperate to regulate mesenchymal proliferation in distinct submesothelial and subepithelial regions. These data provide a molecular mechanism by which mesothelial and epithelial FGF9 directs lung development by regulating mesenchymal growth, and the pattern and expression levels of mesenchymal growth factors that signal back to the epithelium.

Defining the origins of Ras/p53-mediated squamous cell carcinoma

The precise identity of cancer cells of origin and the molecular events of tumor initiation in epidermal squamous cell carcinoma (SCC) are unknown. Here we show that malignancy potential is related to the developmental capacity of the initiating cancer cell in a genetically defined, intact, and inducible in vivo model. Specifically, these data demonstrate that SCCs can originate from inside the hair follicle stem cell (SC) niche or from immediate progenitors, whereas more developmentally restricted progeny, the transit amplifying (TA) cells, are unable to generate even benign tumors in the same genetic context. Using a temporal model of tumorigenesis in situ, we highlight the phenotypes of cancer progression from the hair follicle SC niche, including hyperplasia, epithelial to mesenchymal transition, and SCC formation. Furthermore, we provide insights into the inability of hair follicle TA cells to respond to tumorigenic stimuli.

FGF9 and SHH regulate mesenchymal Vegfa expression and development of the pulmonary capillary network

The juxtaposition of a dense capillary network to lung epithelial cells is essential for air-blood gas exchange. Defective lung vascular development can result in bronchopulmonary dysplasia and alveolar capillary dysplasia. Although vascular endothelial growth factor A (Vegfa) is required for formation of the lung capillary network, little is known regarding the factors that regulate the density and location of the distal capillary plexus and the expression pattern of Vegfa. Here, we show that fibroblast growth factor 9 (FGF9) and sonic hedgehog (SHH) signaling to lung mesenchyme, but not to endothelial cells, are each necessary and together sufficient for distal capillary development. Furthermore, both gain- and loss-of-function of FGF9 regulates Vegfa expression in lung mesenchyme, and VEGF signaling is required for FGF9-mediated blood vessel formation. FGF9, however, can only partially rescue the reduction in capillary density found in the absence of SHH signaling, and SHH is unable to rescue the vascular phenotype found in Fgf9-/- lungs. Thus, both signaling systems regulate distinct aspects of vascular development in distal lung mesenchyme. These data suggest a molecular mechanism through which FGF9 and SHH signaling coordinately control the growth and patterning of the lung capillary plexus, and regulate the temporal and spatial expression of Vegfa.

An FGF-WNT gene regulatory network controls lung mesenchyme development

Lung mesenchyme is a critical determinant of the shape and size of the lung, the extent and patterning of epithelial branching, and the formation of the pulmonary vasculature and interstitial mesenchymal components of the adult lung. Fibroblast growth factor 9 (FGF9) is a critical regulator of lung mesenchymal growth; however, upstream mechanisms that modulate the FGF mesenchymal signal and the downstream targets of mesenchymal FGF signaling are poorly understood. Here we have identified a robust regulatory network in which mesenchymal FGF signaling regulates beta-Catenin mediated WNT signaling in lung mesenchyme. By conditionally inactivating beta-Catenin in lung mesenchyme, we show that mesenchymal WNT-beta-Catenin signaling is essential for lung development and acts to regulate the cell cycle G1 to S transition and the FGF responsiveness of mesenchyme. Together, both FGF and WNT signaling pathways function to sustain mesenchymal growth and coordinate epithelial morphogenesis during the pseudoglandular stage of lung development.

Reciprocal epithelial-mesenchymal FGF signaling is required for cecal development

Fibroblast growth factor (FGF) signaling mediates reciprocal mesenchymal-epithelial cell interactions in the developing mouse lung and limb. In the gastrointestinal (GI) tract, FGF10 is expressed in the cecal mesenchyme and signals to an epithelial splice form of FGF receptor (FGFR) 2 to regulate epithelial budding. Here, we identify FGF9 as a reciprocal epithelial-mesenchymal signal required for cecal morphogenesis. Fgf9 null (Fgf9-/-) mouse embryos have agenesis of the embryonic cecum, lacking both mesenchymal expansion and an epithelial bud. In the cecal region of Fgf9-/- embryos, mesenchymal expression of Fgf10 and Bmp4 is notably absent, whereas the expression of epithelial markers, such as sonic hedgehog, is not affected. Using epithelial and whole explant cultures, we show that FGF9 signals to mesenchymal FGFRs and that FGF10 signals to epithelial FGFRs. Taken together, these data show that an epithelial FGF9 signal is necessary for the expansion of cecal mesenchyme and the expression of mesenchymal genes that are required for epithelial budding. Thus, these data add to our understanding of FGF-mediated reciprocal epithelial-mesenchymal signaling.

Refining the role for adult stem cells as cancer cells of origin

Significant progress has been made to identify the cells at the foundation of tumorigenesis, the cancer cell of origin (CCO). The majority of data points towards resident adult stem cells (ASCs) or primitive progenitors as the CCO for those cancers studied, highlighting the importance of stem cells not only as propagators but also as initiators of cancer. Recent data suggest tumor initiation at the CCOs can be regulated through both intrinsic and extrinsic signals and that the identity of the CCOs and their propensity to initiate tumorigenesis is context dependent. In this review, we summarize some of the recent findings regarding CCOs and solid tumor initiation and highlight its relation with bona fide human cancer.

Genetic studies on the functional relevance of the protein prenyltransferases in skin keratinocytes

The modification of proteins with farnesyl or geranylgeranyl lipids, a process called protein prenylation, facilitates interactions of proteins with membrane surfaces. Protein prenylation is carried out by a pair of cytosolic enzymes, protein farnesyltransferase (FTase) and protein geranylgeranyltransferase type I (GGTase-I). FTase and GGTase-I have attracted interest as therapeutic targets for both cancer and progeria, but very little information exists on the importance of these enzymes for homeostasis of normal tissues. One study actually suggested that FTase is entirely dispensable. To explore the importance of the protein prenyltransferases for normal tissues, we used conditional knockout alleles for Fntb and Pggt1b (which encode the beta-subunits of FTase and GGTase-I, respectively) and a keratin 14-Cre transgene to create mice lacking FTase or GGTase-I in skin keratinocytes. Keratinocyte-specific Fntb knockout mice were viable but developed severe alopecia. Although hair follicles appeared normal during development, they were morphologically abnormal after birth, and ultrastructural and immunohistochemical studies revealed many apoptotic cells. The interfollicular epidermis of Fntb-deficient mice appeared normal; however, keratinocytes from these mice could not proliferate in culture. As expected, non-farnesylated prelamin A and non-farnesylated DNAJA1 accumulated in Fntb-deficient keratinocytes. Keratinocyte-specific Pggt1b knockout mice survived development but died shortly after birth. Like Fntb-deficient keratinocytes, Pggt1b-deficient keratinocytes did not proliferate in culture. Thus, both FTase and GGTase-I are required for the homeostasis of skin keratinocytes.

Clinical outcomes after withdrawal of anti–tumor necrosis factor α therapy in patients with juvenile idiopathic arthritis: A twelve-year experience

OBJECTIVE To estimate the length of time to disease flare and the likelihood of achieving clinical remission after discontinuation of treatment with tumor necrosis factor α (TNFα) blockers in patients with juvenile idiopathic arthritis (JIA). METHODS We conducted a retrospective chart review in a cohort of patients with JIA treated with TNFα inhibitors between January 1, 1998 and November 1, 2009. Demographic information, laboratory data, and medication exposure were extracted using a standardized tool. Outcomes of interest were based on preliminary criteria for remission in JIA. RESULTS One hundred seventy-one patients with 255 discrete episodes of anti-TNFα treatment were reviewed. The median duration of patient observation was 59.7 months (range 5.8-211.2 months). Among patients in whom disease was inactive after discontinuation of anti-TNFα therapy, 50% had persistently inactive disease at 6 months, and 33% had clinical remission at 12 months. The median duration of anti-TNFα therapy after inactive disease was obtained was 6.1 months (range 0-67.9 months). No significant association was observed between the time to disease flare after cessation of treatment with TNFα antagonists and the length of time from the diagnosis of JIA to the initiation of anti-TNFα therapy, the duration of therapy following the onset of inactive disease, or the total duration of treatment with TNFα antagonists prior to discontinuation. The category of JIA, sex, and age at diagnosis were not associated with the risk of relapse. CONCLUSION One-third of patients with JIA can successfully undergo withdrawal of treatment with TNFα antagonists and be spared the cost and potential morbidity of treatment for at least 12 months. Further studies are needed to identify factors to accurately identify these patients.

Recurrent Parotitis as a Presentation of Primary Pediatric Sjögren Syndrome

Parotitis is a common condition seen in the pediatric population, usually as an isolated occurrence associated with viral or bacterial infection. The differential diagnosis expands when recurrent parotitis is encountered. One etiology is primary pediatric Sjögren syndrome (SS), an autoimmune condition typically associated with dryness of the eyes and mouth in adults. Pediatric patients often present with isolated recurrent bilateral parotitis, however, and we describe 4 such cases in children aged 9 to 17 years at presentation. Despite lack of ocular complaints, 3 of these patients had ocular findings on ophthalmologic exam. Our patients also exhibited classic laboratory abnormalities, including positive antinuclear antibody, SS A, and SS B antibodies; presence of rheumatoid factor; and hypergammaglobulinemia. Consideration of SS in the child with recurrent parotitis is important for timely and appropriate referral and treatment. We review the differential diagnosis of parotitis in children as well as the salient features of pediatric SS.

Hemorrhage Rates From Brain Arteriovenous Malformation in Patients With Hereditary Hemorrhagic Telangiectasia

Background and Purpose— Hereditary hemorrhagic telangiectasia (HHT) is a systemic disease characterized by mucocutaneous telangiectasias, epistaxis, and arteriovenous malformations (AVMs). Intracranial hemorrhage (ICH) rates in this population are not well described. We report ICH rates and characteristics in HHT patients with brain AVMs (HHT-BAVMs). Methods— We studied the first 153 HHT-BAVM patients with follow-up data enrolled in the Brain Vascular Malformation Consortium HHT Project. We estimated ICH rates after BAVM diagnosis. Results— The majority of patients were women (58%) and white (98%). The mean age at BAVM diagnosis was 31±19 years (range, 0–70), with 61% of cases diagnosed on asymptomatic screening. Overall, 14% presented with ICH; among symptomatic cases, 37% presented ruptured. During 493 patient-years of follow-up, 5 ICH events occurred yielding a rate of 1.02% per year (95% confidence interval, 0.42–2.44%). ICH-free survival differed significantly by ICH presentation (P=0.003); ruptured cases had a higher ICH rate (10.07%; 95% confidence interval, 3.25–31.21%) than unruptured cases (0.43%; 95% confidence interval, 0.11–1.73%). Conclusions— Patients with HHT-BAVM who present with hemorrhage are at a higher risk for rehemorrhage compared with patients with BAVM detected presymptomatically.