Faculty Bibliography

BACKGROUND: Lipoprotein(a) [Lp(a)] is an inherited atherogenic lipoprotein and an independent risk factor for atherosclerotic cardiovascular disease; however, its clinical role remains limited. OBJECTIVE: We hypothesized that Lp(a) screening in high cardiovascular risk patients could provide insight into disease pathogenesis and modify physician behavior for treatment intensification targeting traditional risk factors when Lp(a)-related risk was identified. METHODS: We screened 113 patients presenting electively for percutaneous coronary intervention (PCI) for Lp(a) who met any of the following criteria: (1) premature coronary artery disease (male age <55 years, female age <65 years); (2) family history of premature coronary artery disease; (3) progression to PCI despite well-controlled traditional risk factors (blood pressure <140/90 mm Hg, and low-density lipoprotein cholesterol <100 mg/dL, and HbA1c <7%, and nonsmoker); or (4) progression to PCI despite at least moderate intensity statin use (simvastatin 40, atorvastatin 40-80, or rosuvastatin 20-40 mg daily). RESULTS: In this high-risk cohort, Lp(a) was elevated in nearly half of all subjects, including those with seemingly well-controlled lipids by prior guidelines, suggesting a role for Lp(a) in conferring residual cardiovascular risk. In our cohort, when screened positive, knowledge of an elevated Lp(a) did not influence referring physicians' treatment intensification targeting traditional modifiable cardiovascular risk factors (P = .18). CONCLUSION: When screened judiciously, elevated levels of Lp(a) are highly prevalent in high cardiovascular risk patients, including at a young age, presenting for PCI and may contribute to previously unappreciated residual cardiovascular risk.

The Lin28a/Let-7 axis has been studied in peripheral tissues for its role in metabolism regulation. However, its central function remains unclear. Here we found that Lin28a is highly expressed in the hypothalamus compared with peripheral tissues. Its expression is positively correlated with positive energy balance, suggesting a potential central role for Lin28a in metabolism regulation. Thus, we targeted the hypothalamic ventromedial nucleus (VMH) to selectively overexpress (Lin28aKI^VMH ) or downregulate (Lin28aKD^VMH ) Lin28a expression in mice. With mice on a standard chow diet, body weight and glucose homeostasis were not affected in Lin28aKI^VMH or Lin28aKD^VMH mice. On a high-fat diet, although no differences in body weight and composition were observed, Lin28aKI^VMH mice showed improved glucose tolerance and insulin sensitivity compared with controls. Conversely, Lin28aKD^VMH mice displayed glucose intolerance and insulin resistance. Changes in VMH AKT activation of diet-induced obese Lin28aKI^VMH or Lin28aKD^VMH mice were not associated with alterations in Let-7 levels or insulin receptor activation. Rather, we observed altered expression of TANK-binding kinase-1 (TBK-1), which was found to be a direct Lin28a target mRNA. VMH-specific inhibition of TBK-1 in mice with diet-induced obesity impaired glucose metabolism and AKT activation. Altogether, our data show a TBK-1-dependent role for central Lin28a in glucose homeostasis.

In this study, we used a polydimethylsiloxane (PDMS)-based platform for the generation of intact, perfusion-competent microvascular networks in vitro. COMSOL Multiphysics, a finite-element analysis and simulation software package, was used to obtain simulated velocity, pressure, and shear stress profiles. Transgene-free human induced pluripotent stem cells (hiPSCs) were differentiated into partially arterialized endothelial cells (hiPSC-ECs) in 5 d under completely chemically defined conditions, using the small molecule glycogen synthase kinase 3β inhibitor CHIR99021 and were thoroughly characterized for functionality and arterial-like marker expression. These cells, along with primary human umbilical vein endothelial cells (HUVECs), were seeded in the PDMS system to generate microvascular networks that were subjected to shear stress. Engineered microvessels had patent lumens and expressed VE-cadherin along their periphery. Shear stress caused by flowing medium increased the secretion of nitric oxide and caused endothelial cells s to align and to redistribute actin filaments parallel to the direction of the laminar flow. Shear stress also caused significant increases in gene expression for arterial markers Notch1 and EphrinB2 as well as antithrombotic markers Kruppel-like factor 2 (KLF-2)/4. These changes in response to shear stress in the microvascular platform were observed in hiPSC-EC microvessels but not in microvessels that were derived from HUVECs, which indicated that hiPSC-ECs may be more plastic in modulating their phenotype under flow than are HUVECs. Taken together, we demonstrate the feasibly of generating intact, engineered microvessels in vitro, which replicate some of the key biological features of native microvessels.

PURPOSE: Fracture nonunion is a common problem for today's orthopaedic surgeon. However, many techniques are currently available for the treatment of long-bone nonunion. This video demonstrates the use of iliac crest bone graft and plate stabilization in the setting of a hypertrophic femoral nonunion. METHODS: Treatment of femoral nonunion after intramedullary nail fixation using compression plating and bone grafting is a reliable technique for reducing pain, improving function, and achieving radiographic union. Furthermore, the use of autologous bone graft, in particular iliac crest bone graft, has provided reliable clinical results. RESULTS: In this video, we present the case of a hypertrophic femoral nonunion treated with supplemental bone grafting in addition to plate and screw fixation. CONCLUSIONS: Although femoral nonunions are a relatively rare occurrence, they can be reasonably treated using stabilization and supplemental bone grafting. Iliac crest bone graft provides for excellent results when used for treatment of a fracture nonunion.

Optic gliomas are brain tumors characterized by slow growth, progressive loss of vision, and limited therapeutic options. Optic gliomas contain various amounts of myxoid matrix, which can represent most of the tumor mass. We sought to investigate biological function and protein structure of the myxoid matrix in optic gliomas to identify novel therapeutic targets. We reviewed histological features and clinical imaging properties, analyzed vasculature by immunohistochemistry and electron microscopy, and performed liquid chromatography-mass spectrometry on optic gliomas, which varied in the amount of myxoid matrix. We found that although subtypes of optic gliomas are indistinguishable on imaging, the microvascular network of pilomyxoid astrocytoma, a subtype of optic glioma with abundant myxoid matrix, is characterized by the presence of endothelium-free channels in the myxoid matrix. These tumors show normal perfusion by clinical imaging and lack histological evidence of hemorrhage organization or thrombosis. The myxoid matrix is composed predominantly of the proteoglycan versican and its linking protein, a vertebrate hyaluronan and proteoglycan link protein 1. We propose that pediatric optic gliomas can maintain blood supply without endothelial cells by using invertebrate-like channels, which we termed primitive myxoid vascularization. Enzymatic targeting of the proteoglycan versican/hyaluronan and proteoglycan link protein 1 rich myxoid matrix, which is in direct contact with circulating blood, can provide novel therapeutic avenues for optic gliomas of childhood.

Regulation of organ growth is a poorly understood process. In the long bones, the growth plates (GPs) drive elongation by generating a scaffold progressively replaced by bone. Although studies have focused on intrinsic GP regulation, classic and recent experiments suggest that local signals also modulate GP function. We devised a genetic mouse model to study extrinsic long bone growth modulation, in which injury is specifically induced in the left hindlimb, such that the right hindlimb serves as an internal control. Remarkably, when only mesenchyme cells surrounding postnatal GPs were killed, left bone growth was nevertheless reduced. GP signaling was impaired by altered paracrine signals from the knee joint, including activation of the injury response and, in neonates, dampened IGF1 production. Importantly, only the combined prevention of both responses rescued neonatal growth. Thus, we identified signals from the knee joint that modulate bone growth and could underlie establishment of body proportions.

The separation of germline from somatic lineages is fundamental to reproduction and species preservation. Here, we show that Drosophila Germ cell-less (GCL) is a critical component in this process by acting as a switch that turns off a somatic lineage pathway. GCL, a conserved BTB (Broad-complex, Tramtrack, and Bric-a-brac) protein, is a substrate-specific adaptor for Cullin3-RING ubiquitin ligase complex (CRL3GCL). We show that CRL3GCL promotes PGC fate by mediating degradation of Torso, a receptor tyrosine kinase (RTK) and major determinant of somatic cell fate. This mode of RTK degradation does not depend upon receptor activation but is prompted by release of GCL from the nuclear envelope during mitosis. The cell-cycle-dependent change in GCL localization provides spatiotemporal specificity for RTK degradation and sequesters CRL3GCL to prevent it from participating in excessive activities. This precisely orchestrated mechanism of CRL3GCL function and regulation defines cell fate at the single-cell level.

Plakophilin-2 (PKP2) is a component of the desmosome and known for its role in cell-cell adhesion. Mutations in human PKP2 associate with a life-threatening arrhythmogenic cardiomyopathy, often of right ventricular predominance. Here, we use a range of state-of-the-art methods and a cardiomyocyte-specific, tamoxifen-activated, PKP2 knockout mouse to demonstrate that in addition to its role in cell adhesion, PKP2 is necessary to maintain transcription of genes that control intracellular calcium cycling. Lack of PKP2 reduces expression of Ryr2 (coding for Ryanodine Receptor 2), Ank2 (coding for Ankyrin-B), Cacna1c (coding for CaV1.2) and Trdn (coding for triadin), and protein levels of calsequestrin-2 (Casq2). These factors combined lead to disruption of intracellular calcium homeostasis and isoproterenol-induced arrhythmias that are prevented by flecainide treatment. We propose a previously unrecognized arrhythmogenic mechanism related to PKP2 expression and suggest that mutations in PKP2 in humans may cause life-threatening arrhythmias even in the absence of structural disease.It is believed that mutations in desmosomal adhesion complex protein plakophilin 2 (PKP2) cause arrhythmia due to loss of cell-cell communication. Here the authors show that PKP2 controls the expression of proteins involved in calcium cycling in adult mouse hearts, and that lack of PKP2 can cause arrhythmia in a structurally normal heart.

Regulatory T (Treg) cell infiltration constitutes a prominent feature of pancreatic ductal adenocarcinoma (PDA). However, the immunomodulatory function of Treg cells in PDA is poorly understood. Here, we demonstrate that Treg cell ablation is sufficient to evoke effective anti-tumor immune response in early and advanced pancreatic tumorigenesis in mice. This response is dependent on interferon-gamma (IFN-gamma)-producing cytotoxic CD8+ T cells. We show that Treg cells engage in extended interactions with tumor-associated CD11c+ dendritic cells (DCs) and restrain their immunogenic function by suppressing the expression of costimulatory ligands necessary for CD8+ T cell activation. Consequently, tumor-associated CD8+ T cells fail to display effector activities when Treg cell ablation is combined with DC depletion. We propose that tumor-infiltrating Treg cells can promote immune tolerance by suppressing tumor-associated DC immunogenicity. The therapeutic manipulation of this axis might provide an effective approach for the targeting of PDA.