PRDM proteins: important players in differentiation and disease.

The PRDM family has recently spawned considerable interest as it has been implicated in fundamental aspects of cellular differentiation and exhibits expanding ties to human diseases. The PRDMs belong to the SET domain family of histone methyltransferases, however, enzymatic activity has been determined for only few PRDMs suggesting that they act by recruiting co-factors or, more speculatively, confer methylation of non-histone targets. Several PRDM family members are deregulated in human diseases, most prominently in hematological malignancies and solid cancers, where they can act as both tumor suppressors or drivers of oncogenic processes. The molecular mechanisms have been delineated for only few PRDMs and little is known about functional redundancy within the family. Future studies should identify target genes of PRDM proteins and the protein complexes in which PRDM proteins reside to provide a more comprehensive understanding of the biological and biochemical functions of this important protein family.

Heat shock protein amplification improves cerebellar myelination in the Npc1nih mouse model.

BACKGROUND: Niemann-Pick disease type C (NPC) is a rare prematurely fatal lysosomal lipid storage disease with limited therapeutic options. The prominent neuropathological hallmarks include hypomyelination and cerebellar atrophy. We previously demonstrated the efficacy of recombinant human heat shock protein 70 (rhHSP70) in preclinical models of the disease. It reduced glycosphingolipid levels in the central nervous system (CNS), improving cerebellar myelination and improved behavioural phenotypes in Npc1nih (Npc1-/-) mice. Furthermore, treatment with arimoclomol, a well-characterised HSP amplifier, attenuated lysosomal storage in NPC patient fibroblasts and improved neurological symptoms in Npc1-/- mice. Taken together, these findings prompted the investigation of the effects of HSP amplification on CNS myelination. METHODS: We administered bimoclomol daily or rhHSP70 6 times per week to Npc1-/- (BALB/cNctr-Npc1m1N/J, also named Npc1nih) mice by intraperitoneal injection from P7 through P34 to investigate the impact on CNS myelination. The Src-kinase inhibitor saracatinib was administered with/without bimoclomol twice daily to explore the contribution of Fyn kinase to bimoclomol's effects. FINDINGS: Treatment with either bimoclomol or rhHSP70 improved myelination and increased the numbers of mature oligodendrocytes (OLs) as well as the ratio of active-to-inactive forms of phosphorylated Fyn kinase in the cerebellum of Npc1-/- mice. Additionally, treatment with bimoclomol preserved cerebellar weight, an effect that was abrogated when co-administered with saracatinib, an inhibitor of Fyn kinase. Bimoclomol-treated mice also exhibited increased numbers of immature OLs within the cortex. INTERPRETATION: These data increase our understanding of the mechanisms by which HSP70 regulates myelination and provide further support for the clinical development of HSP-amplifying therapies in the treatment of NPC. FUNDING: Funding for this study was provided by Orphazyme A/S (Copenhagen, Denmark) and a Pathfinder Award from The Wellcome Trust.

Animal models for Niemann-Pick type C: implications for drug discovery & development.

INTRODUCTION: Niemann-Pick type C (NPC) is a neurovisceral, progressively detrimental lysosomal storage disease with very limited therapeutic options and no approved treatment available in the US. Despite its rarity, NPC has seen increased drug developmental efforts over the past decade, culminating in the completion of two potential registration trials in 2018. Areas covered: This review highlights the many available animal models that have been developed in the field and briefly covers classical and new cell technologies. This review provides a high-level evaluation and prioritization of the various models with regard to efficient and clinically translatable drug development, and briefly discusses the relevant developments and opportunities pertaining to this. Expert opinion: With a number of in vitro and in vivo models available, and with having several drugs, all with various mechanisms of action, either approved or in late stage development, the NPC field is in an exciting time. One of the challenges for researchers and developers will be the ability to make use of the lessons learnt from existing late-stage programs as well as the incorporation not only of the opportunities but also the limitations of the many models into successful drug discovery and translational development programs.

The heat shock protein amplifier arimoclomol improves refolding, maturation and lysosomal activity of glucocerebrosidase.

BACKGROUND: Gaucher Disease is caused by mutations of the GBA gene which encodes the lysosomal enzyme acid beta-glucosidase (GCase). GBA mutations commonly affect GCase function by perturbing its protein homeostasis rather than its catalytic activity. Heat shock proteins are well known cytoprotective molecules with functions in protein homeostasis and lysosomal function and their manipulation has been suggested as a potential therapeutic strategy for GD. The investigational drug arimoclomol, which is in phase II/III clinical trials, is a well-characterized HSP amplifier and has been extensively clinically tested. Importantly, arimoclomol efficiently crosses the blood-brain-barrier presenting an opportunity to target the neurological manifestations of GD, which remains without a disease-modifying therapy. METHODS: We used a range of biological and biochemical in vitro assays to assess the effect of arimoclomol on GCase activity in ex vivo systems of primary fibroblasts and neuronal-like cells from GD patients. FINDINGS: We found that arimoclomol induced relevant HSPs such as ER-resident HSP70 (BiP) and enhanced the folding, maturation, activity, and correct cellular localization of mutated GCase across several genotypes including the common L444P and N370S mutations in primary cells from GD patients. These effects where recapitulated in a human neuronal model of GD obtained by differentiation of multipotent adult stem cells. INTERPRETATION: These data demonstrate the potential of HSP-targeting therapies in GCase-deficiencies and strongly support the clinical development of arimoclomol as a potential therapeutic option for the neuronopathic forms of GD. FUNDING: The research was funded by Orphazyme A/S, Copenhagen, Denmark.

Chromatin-modifying proteins in cancer.

Chromatin-modifying proteins mold the genome into areas that are accessible for transcriptional activity and areas that are transcriptionally silent. This epigenetic gene regulation allows for different transcriptional programs to be conducted in different cell types at different timepoints-despite the fact that all cells in the organism contain the same genetic information. A large amount of data gathered over the last decades has demonstrated that deregulation of chromatin-modifying proteins is etiologically involved in the development and progression of cancer. Here we discuss how epigenetic alterations influence cancer development and review known cancer-associated alterations in chromatin-modifying proteins.

PRDM11 is dispensable for the maintenance and function of hematopoietic stem and progenitor cells.

Hematopoietic stem cells (HSC)(1) supply organisms with life-long output of mature blood cells. To do so, the HSC pool size has to be maintained by HSC self-renewing divisions. PRDM3 and PRDM16 have been documented to regulate HSC self-renewal, maintenance and function. We found Prdm11 to have similar expression patterns in the hematopoietic stem and progenitor cell (HSPC) compartments as Prdm3 and Prdm16. Therefore, we undertook experiments to test if PRDM11 regulates HSC self-renewal, maintenance and function by investigating the Prdm11(-/-) mice. Our data shows that phenotypic HSPCs are intact in bone marrow (BM) of one-year-old Prdm11(-/-) mice. In addition, Prdm11(-/-) mice were able to fully regenerate the hematopoietic system upon BM transplantation (BMT) into lethally irradiated mice with a mild drop in lymphoid output only. Taken together, this suggests that PRDM11, in contrast to PRDM3 and PRDM16, is not directly involved in regulation of HSPCs in mice.