Person:

Mazitschek, Ralph

Chromatin modifications, especially histone-tail acetylation, have been implicated in memory formation. Increased histone-tail acetylation induced by inhibitors of histone deacetylases (HDACis) facilitates learning and memory in wild-type mice as well as in mouse models of neurodegeneration. Harnessing the therapeutic potential of HDACis requires knowledge of the specific HDAC family member(s) linked to cognitive enhancement. Here we show that neuron-specific overexpression of HDAC2, but not that of HDAC1, decreased dendritic spine density, synapse number, synaptic plasticity and memory formation. Conversely, Hdac2 deficiency resulted in increased synapse number and memory facilitation, similar to chronic treatment with HDACis in mice. Notably, reduced synapse number and learning impairment of HDAC2-overexpressing mice were ameliorated by chronic treatment with HDACis. Correspondingly, treatment with HDACis failed to further facilitate memory formation in Hdac2-deficient mice. Furthermore, analysis of promoter occupancy revealed an association of HDAC2 with the promoters of genes implicated in synaptic plasticity and memory formation. Taken together, our results suggest that HDAC2 functions in modulating synaptic plasticity and long-lasting changes of neural circuits, which in turn negatively regulates learning and memory. These observations encourage the development and testing of HDAC2-selective inhibitors for human diseases associated with memory impairment.

Neurite growth requires two guanine nucleotide-binding protein polymers of tubulins and septins. However, whether and how those cytoskeletal systems are coordinated was unknown. Here we show that the acute knockdown or knockout of the pivotal septin subunit SEPT7 from cerebrocortical neurons impairs their interhemispheric and cerebrospinal axon projections and dendritogenesis in perinatal mice, when the microtubules are severely hyperacetylated. The resulting hyperstabilization and growth retardation of microtubules are demonstrated in vitro. The phenotypic similarity between SEPT7 depletion and the pharmacological inhibition of α-tubulin deacetylase HDAC6 reveals that HDAC6 requires SEPT7 not for its enzymatic activity, but to associate with acetylated α-tubulin. These and other findings indicate that septins provide a physical scaffold for HDAC6 to achieve efficient microtubule deacetylation, thereby negatively regulating microtubule stability to an optimal level for neuritogenesis. Our findings shed light on the mechanisms underlying the HDAC6-mediated coupling of the two ubiquitous cytoskeletal systems during neural development.

We report an improved variant of mKeima, a monomeric long Stokes shift red fluorescent protein, hmKeima8.5. The increased intracellular brightness and large Stokes shift (∼180 nm) make it an excellent partner with teal fluorescent protein (mTFP1) for multiphoton, multicolor applications. Excitation of this pair by a single multiphoton excitation wavelength (MPE, 850 nm) yields well-separable emission peaks (∼120-nm separation). Using this pair, we measure homo- and hetero-oligomerization interactions in living cells via multiphoton excitation fluorescence correlation spectroscopy (MPE-FCS). Using tandem dimer proteins and small-molecule inducible dimerization domains, we demonstrate robust and quantitative detection of intracellular protein–protein interactions. We also use MPE-FCCS to detect drug–protein interactions in the intracellular environment using a Coumarin 343 (C343)-conjugated drug and hmKeima8.5 as a fluorescence pair. The mTFP1/hmKeima8.5 and C343/hmKeima8.5 combinations, together with our calibration constructs, provide a practical and broadly applicable toolbox for the investigation of molecular interactions in the cytoplasm of living cells.

Background: Drug resistance remains a major public health challenge for malaria treatment and eradication. Individual loci associated with drug resistance to many antimalarials have been identified, but their epistasis with other resistance mechanisms has not yet been elucidated. Results: We previously described two mutations in the cytoplasmic prolyl-tRNA synthetase (cPRS) gene that confer resistance to halofuginone. We describe here the evolutionary trajectory of halofuginone resistance of two independent drug resistance selections in Plasmodium falciparum. Using this novel methodology, we discover an unexpected non-genetic drug resistance mechanism that P. falciparum utilizes before genetic modification of the cPRS. P. falciparum first upregulates its proline amino acid homeostasis in response to halofuginone pressure. We show that this non-genetic adaptation to halofuginone is not likely mediated by differential RNA expression and precedes mutation or amplification of the cPRS gene. By tracking the evolution of the two drug resistance selections with whole genome sequencing, we further demonstrate that the cPRS locus accounts for the majority of genetic adaptation to halofuginone in P. falciparum. We further validate that copy-number variations at the cPRS locus also contribute to halofuginone resistance. Conclusions: We provide a three-step model for multi-locus evolution of halofuginone drug resistance in P. falciparum. Informed by genomic approaches, our results provide the first comprehensive view of the evolutionary trajectory malaria parasites take to achieve drug resistance. Our understanding of the multiple genetic and non-genetic mechanisms of drug resistance informs how we will design and pair future anti-malarials for clinical use. Electronic supplementary material The online version of this article (doi:10.1186/s13059-014-0511-2) contains supplementary material, which is available to authorized users.

Synaptic function is affected in many brain diseases and disorders. Technologies for large-scale synapse assays can facilitate identification of drug leads. Here we report a “synapse microarray” technology that enables ultra-sensitive, high-throughput, and quantitative screening of synaptogenesis. Our platform enables the induction of synaptic structures in regular arrays by precise positioning of non-neuronal cells expressing synaptic proteins, while allowing neurites to grow freely around these cells. The technology increases by tenfold the sensitivity of the traditional assays, and simultaneously decreases the time required to capture synaptogenic events by an order of magnitude. It is readily incorporated into multiwell formats compatible with industrial high-throughput screening platforms. Using this technology, we screened a chemical library and identified novel histone deacetylase inhibitors that improve neuroligin-1 induced synaptogenesis via modulating class-I histone deacetylases. We also found a structure-activity relationship for designing novel potent histone deacetylase inhibitors, which can be applied towards development of new therapeutics.

Introduction: Medulloblastoma (MB) is the most frequent malignant brain tumor in children. Four subgroups with distinct genetic, epigenetic and clinical characteristics have been identified. Survival remains particularly poor in patients with Group 3 tumors harbouring a MYC amplification. We herein explore the molecular mechanisms and translational implications of class I histone deacetylase (HDAC) inhibition in MYC driven MBs. Material and Methods Expression of HDACs in primary MB subgroups was compared to normal brain tissue. A panel of MB cell lines, including Group 3 MYC amplified cell lines, were used as model systems. Cells were treated with HDAC inhibitors (HDACi) selectively targeting class I or IIa HDACs. Depletion of HDAC2 was performed. Intracellular HDAC activity, cellular viability, metabolic activity, caspase activity, cell cycle progression, RNA and protein expression were analyzed. Results: HDAC2 was found to be overexpressed in MB subgroups with poor prognosis (SHH, Group 3 and Group 4) compared to normal brain and the WNT subgroup. Inhibition of the enzymatic activity of the class I HDACs reduced metabolic activity, cell number, and viability in contrast to inhibition of class IIa HDACs. Increased sensitivity to HDACi was specifically observed in MYC amplified cells. Depletion of HDAC2 increased H4 acetylation and induced cell death. Simulation of clinical pharmacokinetics showed time-dependent on target activity that correlated with binding kinetics of HDACi compounds. Conclusions: We conclude that HDAC2 is a valid drug target in patients with MYC amplified MB. HDACi should cover HDAC2 in their inhibitory profile and timing and dosing regimen in clinical trials should take binding kinetics of compounds into consideration. Electronic supplementary material The online version of this article (doi:10.1186/s40478-015-0201-7) contains supplementary material, which is available to authorized users.

A library of approximately 2000 small molecules biased toward inhibition of histone deacetylases was assayed for antimalarial activity in a high-throughput P. falciparum viability assay. Active compounds were cross-analyzed for induction of histone hyperacetylation in a human myeloma cell line to identify HDAC inhibitors with selectivity for P. falciparum over the human host. To verify on-target selectivity, pfHDAC-1 was expressed and purified and a biochemical assay for pfHDAC-1 activity was established.

Epigenetic gene regulation is a dynamic process orchestrated by chromatin-modifying enzymes. Many of these master regulators exert their function through covalent modification of DNA and histone proteins. Aberrant epigenetic processes have been implicated in the pathophysiology of multiple human diseases. Small-molecule inhibitors have been essential to advancing our understanding of the underlying molecular mechanisms of epigenetic processes. However, the resolution offered by small molecules is often insufficient to manipulate epigenetic processes with high spatio-temporal control. Here, we present a novel and generalizable approach, referred to as ‘Chemo-Optical Modulation of Epigenetically-regulated Transcription’ (COMET), enabling high-resolution, optical control of epigenetic mechanisms based on photochromic inhibitors of human histone deacetylases using visible light. COMET probes may translate into novel therapeutic strategies for diseases where conditional and selective epigenome modulation is required.

Small molecule fluorophores are indispensable tools for modern biomedical imaging techniques. In this report, we present the development of a new class of BODIPY dyes based on an alkoxy-fluoro-boron-dipyrromethene core. These novel fluorescent dyes, which we term MayaFluors, are characterized by good aqueous solubility and favorable in vitro physicochemical properties. MayaFluors are readily accessible in good yields in a one-pot, two-step approach starting from well-established BODIPY dyes, and allow for facile modification with functional groups of relevance to bioconjugate chemistry and bioorthogonal labeling. Biological profiling in living cells demonstrates excellent membrane permeability, low nonspecific binding, and lack of cytotoxicity.

ACY-241 is a novel, orally available and selective histone deacetylase (HDAC) 6 inhibitor in Phase 1b clinical development in multiple myeloma (NCT 02400242). Like the structurally related drug ACY-1215 (ricolinostat), ACY-241 has the potential for a substantially reduced side effect profile versus current nonselective HDAC inhibitor drug candidates due to reduced potency against Class I HDACs while retaining the potential for anticancer effectiveness. We now show that combination treatment of xenograft models with paclitaxel and either ricolinostat or ACY-241 significantly suppresses solid tumor growth. In cell lines from multiple solid tumor lineages, combination treatment with ACY-241 and paclitaxel enhanced inhibition of proliferation and increased cell death relative to either single agent alone. Combination treatment with ACY-241 and paclitaxel also resulted in more frequent occurrence of mitotic cells with abnormal multipolar spindles and aberrant mitoses, consistent with the observed increase of aneuploid cells. At the molecular level, multipolar mitotic spindle formation was observed to be NuMA-dependent and γ-tubulin independent, suggesting that treatment-induced multipolar spindle formation does not depend on centrosomal amplification. The significantly enhanced efficacy of ACY-241 plus paclitaxel observed here, in addition to the anticipated superior safety profile of a selective HDAC6 inhibitor versus pan-HDAC inhibitors, provides a strong rationale for clinical development of this combination in patients with advanced solid tumors.