Daniel Raben Ph. D.

Research Interests

Biochemistry and chemistry of lipids and lipid metabolizing enzymes involved in signaling cascades

A major effort in our laboratory is focused on understanding the biochemistry and chemistry underlying the molecular aspects involved in regulating lipid metabolizing signaling enzymes and the physiological roles of this regulation. Control of lipid metabolizing enzymes involves the modulation of two key parameters; their sub-cellular distribution and their intrinsic enzymatic activity. Our studies have concentrated on three families of lipid-metabolizing signaling enzymes: diacylglycerol kinases, phospholipases D, and phospholipases C.

Specific Areas of Interest

Interfacial Enzymology of Lipid Metabolizing Signaling Enzymes: We are particularly interested in identifying the critical modulating proteins, lipids, and post-translational modifications that alter the localization and/or activity of lipid metabolizing enzymes.  In these studies we consider the fact that these enzymes act as interfacial enzymes and their regulation includes a number of interfacial-dependent parameters.  Our recent studies have identified some of the diacylglycerol metabolizing enzyme DGK-θ (diacylglycerol kinase-theta) interfacial parameters that are altered upon neuronal depolarization.  Further, our studies demonstrated that activation of DGK-θ requires a protein that contains a polybasic region.  We have recently obtained evidence that identifies at least one, if not only, activator binding domain on DGK-θ.

Enzyme Structure/Function Studies: We are also interested in the structural components of these enzymes that are critical for their distribution/re-distribution to specific sub-cellular compartments.  Additionally, and to compliment the enzymology studies, we are interested in elucidating the catalytic mechanism(s) of these enzymes.  These studies will be conducted partly in collaboration with Dr. Mario Amzel.  Our long-term goal is to understand the biochemistry and chemistry of these enzymes and determine how changes in their sub-cellular localization and/or enzymatic activity affect their signaling functions.

Physiological Functions of DGKs in Neurons: There is growing evidence that DGKs play physiological roles in mammalian neurons. This evidence includes cellular localization of specific isoforms, and the observations that likely modulate (a) susceptibility to epileptic seizures (DGK-ε), (b) neuronal spine density (DGK-ζ and DGK-β), and (c) pre-synaptic glutamate release during DHPG (3,5-dihydroxyphenylglycine)-induced long-term potentiation (DGK-ι).  We are currently examining the role of DGK-θ in glutamatergic neurons.  These studies have initially focused on identifying the physiologic regulator of DGK-θ, and test the hypothesis that this enzyme modulates induced glutamate release in these mammalian neurons.  We discovered that DGK-θ modulates glutamate release from cortical and hippocampal neurons in part by modulating synaptic vesicle cycling.  These studies are conducted in collaboration with Dr. Rick Huganier’s laboratory.

Roger H. Reeves

Research Interests

Molecular genetic basis of and therapies for Down syndrome

Down syndrome (DS) occurs as a result of Trisomy 21 and is among the most complicated genetic conditions compatible with human survival. The Reeves laboratory complements genetic analyses in human beings with the creation and characterization of mouse models to understand why and how gene dosage imbalance disrupts development in DS. The models then provide a basis to explore therapeutic approaches to amelioration of DS features. We use chromosome engineering in ES cells to create defined dosage imbalance in order to localize the genes contributing to these anomalies and to test directly hypotheses concerning Down syndrome “critical regions” on human chromosome 21. Quantitative phenotypic assays that we have developed give a precise and sensitive readout of the relative effects on phenotype when overlapping subsets of genes are at dosage imbalance. Developmental analyses of these traits are underway to identify the timing and location of divergence between trisomic and euploid fetuses. We have used mouse models to:

  1. validate epidemiological findings suggesting a lower incidence of cancer in Down syndrome and to identify the candidate genes (Sussan et al., 2008; Yang and Reeves, 2011 and 2016);
  2. identify direct parallels in the development of the craniofacial skeleton in Down syndrome and trisomic mice (see Hill et al., 2007; Starbuck et al., 2011) and how this is affected by therapies aimed at over-coming Shh response deficits (N. Singh et al., 2015 and 2016);
  3. establish that deficits in cranial neural crest delamination, migration and proliferation are the primary contributors to the hypomorphic craniofacial skeleton (Roper et al., 2009);
  4. identify genetic modifiers of congenital heart disease in the genetically sensitized Down syndrome population with biological validation in animal models (Ramachandran et al., 2014 and 2016; Li, Cherry et al., 2012; Li, Edie et al., 2016);
  5. discover the basis for and potential “treatment” of a fundamental structural deficit in the trisomic brain (Roper et al., 2006; Currier et al., 2012; Das et al. 2013; Dutka et al. 2015) and why some trisomic cells respond less than euploid cells to the mitogenic effects of Shh growth factor.

With fellow PI Stephanie Sherman, we assess genetic contributions to variation in intellectual ability in the Down Syndrome Cognition Project (DS Cognition Project). We use the Arizona Cognitive Test Battery (Edgin et al., 2010) to assess cognitive ability based on functions mapped to different brain regions that are often affected in Down syndrome. Johns Hopkins School of Medicine and the Kennedy Krieger Institute are a site for the ongoing Roche Clinical trial, BP 25543.

Definition of the timing and location of divergence between trisomic and euploid phenotypes and of the gene(s) primarily contributing to those differences provides the necessary basis for genetic, pharmacologic and stem cell therapies to ameliorate these anomalies (Das and Reeves, 2011; Haydar and Reeves, 2012).