Faculty Bibliography

Background: Plakophilin-2 (PKP2) is classically defined as a protein of the desmosome, an intercellular adhesion structure that also acts as a signaling hub to maintain structural and electrical homeostasis. Mutations in PKP2 associate with most cases of gene-positive arrhythmogenic right ventricular cardiomyopathy (ARVC). A better understanding of PKP2 cardiac biology can help elucidate the mechanisms underlying arrhythmic and cardiomyopathic events that occur consequent to its mutation. Here we sought to captureearly molecular/cellular events that can act as nascent substrates for subsequent arrhythmic/cardiomyopathic phenotypes.
Method(s): We used multiple quantitative imaging modalities, as well as biochemical and high-resolution mass spectrometry methods to study the functional/structural properties of cells/tissues derived from cardiomyocytespecific, tamoxifen-activated, PKP2 knockout mice ("PKP2cKO"). Studies were carried out 14 days post-tamoxifen injection, a time point preceding an overt electrical or structural phenotype.Myocytes from right or left ventricular free wall were studied separately, to detect functional/structural asymmetries.
Result(s): Most properties of PKP2cKO left ventricular (LV) myocytes were not different from control; in contrast, PKP2cKO right ventricular (RV) myocytes showed increased amplitude and duration of Ca2+transients, increased frequency of spontaneous Ca2+release events, increased [Ca2+] in the cytoplasm and sarcoplasmic reticulum compartments, and dynamic Ca2+accumulation in mitochondria. In addition, RyR2 in RV presented enhanced sensitivity to Ca2+and preferential phosphorylation in a domain known to modulate Ca2+gating. RNAseq at 14 days post-TAM showed no relevant difference in transcript abundance between RV and LV, neither in control nor in PKP2cKO cells, suggesting that in the earliest stage, [Ca2+]i dysfunction is not transcriptional. Rather, we found an RV-predominant increase in membrane permeability that can permit Ca2+entry into the cell. Cx43 ablation mitigated the increase in membrane permeability, the accumulation of cytoplasmic Ca2+and the early stages of RV dysfunction.
Conclusion(s): Loss of PKP2 creates an RV-predominant arrhythmogenic substrate (Ca2+ dysregulation) that precedes the cardiomyopathy and that is, at least in part, mediated by a Cx43-dependent membrane conduit. Given that asymmetric Ca2+ dysregulation precedes the cardiomyopathic stage, we speculate that abnormal Ca2+ handling in RV myocytes can be a trigger for gross structural changes observed at a later stage

Cell fate transitions are accompanied by global transcriptional, epigenetic and topological changes driven by transcription factors, as is exemplified by reprogramming somatic cells to pluripotent stem cells through the expression of OCT4, KLF4, SOX2 and cMYC. How transcription factors orchestrate the complex molecular changes around their target gene loci remains incompletely understood. Here, using KLF4 as a paradigm, we provide a transcription-factor-centric view of chromatin reorganization and its association with three-dimensional enhancer rewiring and transcriptional changes during the reprogramming of mouse embryonic fibroblasts to pluripotent stem cells. Inducible depletion of KLF factors in PSCs caused a genome-wide decrease in enhancer connectivity, whereas disruption of individual KLF4 binding sites within pluripotent-stem-cell-specific enhancers was sufficient to impair enhancer-promoter contacts and reduce the expression of associated genes. Our study provides an integrative view of the complex activities of a lineage-specifying transcription factor and offers novel insights into the nature of the molecular events that follow transcription factor binding.

Background/Purpose : Sarilumab blocks interleukin-6 (IL-6) from binding to membrane and soluble IL-6 receptor-alpha. Sarilumab is approved for adults with rheumatoid arthritis (RA) and is being investigated in a Phase 2 trial (NCT02776735) in 2-17-year-old patients (pts) with polyarticular-course juvenile idiopathic arthritis (pcJIA), comprising rheumatoid-factor (RF)-positive and RF-negative polyarticular and extended oligoarticular JIA. This study aimed to evaluate pharmacokinetics (PK), pharmacodynamics (PD), safety, and efficacy of 3 subcutaneous (SC) sarilumab doses in pcJIA. Methods : A 12-week dose-finding study was performed to identify an appropriate sarilumab dose for use in the pcJIA population. Pts were divided by body weight into 2 groups: A (30-60 kg) and B (10-< 30 kg), and received sequential ascending doses of sarilumab, Dose 1 (Group A/B): 2.0/2.5 mg/kg q2w; Dose 2 (Group A/B): 3/4 mg/kg q2w; and Dose 3 (Group A/B): 2.0/2.5 mg/kg qw. pcJIA doses were targeted to achieve similar exposure to adult RA doses (150 mg q2w, 200 mg q2w, and 150 mg qw). Primary outcome was PK; secondary outcomes were safety, PD, and efficacy of sarilumab. Results : 42 pts enrolled (20/22 in Groups A/B); mean age was 13.0/5.2 years. At baseline, mean pcJIA duration, number of active joints, and JADAS27-CRP were 4.6/1.7 years, 17.2/11.0, and 22.2/19.1, in Groups A/B, respectively. As in adult pts, sarilumab exhibited nonlinear PK with target-mediated drug disposition (TMDD). Following repeated SC administrations, exposure increased in a greater than dose-proportional manner and accumulated 1.9-4.5-fold over 12 weeks. Sarilumab exposure was similar in both weight groups for each dose (Figure), and comparable to corresponding adult doses. Treatment-emergent adverse events (AEs) were reported in 36/42 (85.7%) pts (comparable across dose and weight groups); infections (28/42, 66.7%) were the most frequently reported AE. 12 grade 3/4 neutropenias were identified, mostly in Dose 3 (n=6) and in Group B (n=8). None was associated with infection; all resolved in a few days. Overall, 4 pts discontinued due to neutropenia and 1 due to alanine aminotransferase increase. There were no serious AEs, no cases of GI perforation, and no deaths. By Week 12, as observed while on-treatment: all pts attained JIA ACR30; 50%, 62%, and 100% of pts attained JIA ACR70 with Doses 1, 2, and 3, respectively; JADAS27-CRP mean % changes from baseline in Doses 1, 2, and 3 were -74.6%, -73.1%, and -87.9%, respectively. Conclusion : Sarilumab exhibited nonlinear PK with TMDD. Doses tested in pcJIA yielded similar exposure in both weight groups and were comparable to equivalent doses in adults with RA. All dose regimens proved effective for decreasing disease activity. Safety profile was consistent with class effects; higher incidences of neutropenia were observed with Dose 3, and in pts weighing 10-< 30 kg

Although glucose-sensing neurons were identified more than 50 years ago, the physiological role of glucose sensing in metazoans remains unclear. Here we identify a pair of glucose-sensing neurons with bifurcated axons in the brain of Drosophila. One axon branch projects to insulin-producing cells to trigger the release of Drosophila insulin-like peptide 2 (dilp2) and the other extends to adipokinetic hormone (AKH)-producing cells to inhibit secretion of AKH, the fly analogue of glucagon. These axonal branches undergo synaptic remodelling in response to changes in their internal energy status. Silencing of these glucose-sensing neurons largely disabled the response of insulin-producing cells to glucose and dilp2 secretion, disinhibited AKH secretion in corpora cardiaca and caused hyperglycaemia, a hallmark feature of diabetes mellitus. We propose that these glucose-sensing neurons maintain glucose homeostasis by promoting the secretion of dilp2 and suppressing the release of AKH when haemolymph glucose levels are high.

Hyaluronan (HA) fragments have been proposed to elicit defensive or pro-inflammatory responses in many cell types. For articular chondrocytes in an inflammatory environment, studies have failed to reach consensus on the endogenous production or effects of added HA fragments. The present study was undertaken to resolve this discrepancy. Cultured primary human articular chondrocytes were exposed to the inflammatory cytokine IL-1β, and then tested for changes in HA content/size in conditioned medium, and for the expression of genes important in HA binding/signaling or metabolism, and in other catabolic/anabolic responses. Changes in gene expression caused by enzymatic degradation of endogenous HA, or addition of exogenous HA fragments, were examined. IL-1β increased the mRNA levels for HA synthases HAS2/HAS3 and for the HA-binding proteins CD44 and TSG-6. mRNA levels for TLR4 and RHAMM were very low and were little affected by IL-1β. mRNA levels for catabolic markers were increased, while type II collagen (α1(II)) and aggrecan were decreased. HA concentration in the conditioned medium was increased, but the HA was not degraded. Treatment with recombinant hyaluronidase or addition of low endotoxin HA fragments did not elicit pro-inflammatory responses. Our findings showed that HA fragments were not produced by IL-1β-stimulated human articular chondrocytes in the absence of other sources of reactive oxygen or nitrogen species, and that exogenous HA fragments from oligosaccharides up to about 40 kDa in molecular mass were not pro-inflammatory agents for human articular chondrocytes, probably due to low expression of TLR4 and RHAMM in these cells.

Uterus transplantation is an emerging technology adding to the arsenal of treatments for infertility; specifically the only available treatment for uterine factor infertility. Ethical investigations concerning risks to uteri donors and transplant recipients have been discussed in the literature. However, missing from the discourse is the potential of uterus transplantation in other groups of genetically XY women who experience uterine factor infertility. There have been philosophical inquiries concerning uterus transplantation in genetically XY women, which includes transgender women and women with complete androgen insufficiency syndrome. We discuss the potential medical steps necessary and associated risks for uterus transplantation in genetically XY women. Presently, the medical technology does not exist to make uterus transplantation a safe and effective option for genetically XY women, however this group should not be summarily excluded from participation in trials. Laboratory research is needed to better understand and reduce medical risk and widen the field to all women who face uterine factor infertility.

Impaired wound healing is a major complication of diabetes and despite the associated risks, treatment strategies for diabetic wounds remain limited. This is due, in part, to an incomplete understanding of the underlying pathological mechanisms, including the effects of hyperglycemia on components of the extracellular matrix (ECM). In the present study, we explored whether the expression of thrombospondin-2 (TSP2), a matricellular protein with a demonstrated role in response to injury, was associated with delayed healing in diabetes. First, we found that TSP2 expression was elevated in diabetic mice and skin from diabetic patients. Then, to determine the contribution of TSP2 to impaired healing in diabetes, we developed a novel diabetic TSP2-deficient model. Though the TSP2 deficient mice developed obesity and hyperglycemia comparable to diabetic control mice, they exhibited significantly improved healing, characterized by accelerated re-epithelialization and increased granulation tissue formation, fibroblast migration, and blood vessel maturation. We further found that hyperglycemia increased TSP2 expression in fibroblasts, the major cellular source of TSP2 in wounds. Mechanistically, high glucose increased activation of the hexosamine pathway and NF-κB signaling to elevate TSP2 expression. Our studies demonstrate that hyperglycemia-induced TSP2 expression contributes to impaired healing in diabetes.

Histone post-translational modifications are key gene expression regulators, but their rapid dynamics during development remain difficult to capture. We applied a Fab-based live endogenous modification labeling technique to monitor the changes in histone modification levels during zygotic genome activation (ZGA) in living zebrafish embryos. Among various histone modifications, H3 Lys27 acetylation (H3K27ac) exhibited most drastic changes, accumulating in two nuclear foci in the 64- to 1k-cell-stage embryos. The elongating form of RNA polymerase II, which is phosphorylated at Ser2 in heptad repeats within the C-terminal domain (RNAP2 Ser2ph), and miR-430 transcripts were also concentrated in foci closely associated with H3K27ac. When treated with α-amanitin to inhibit transcription or JQ-1 to inhibit binding of acetyl-reader proteins, H3K27ac foci still appeared but RNAP2 Ser2ph and miR-430 morpholino were not concentrated in foci, suggesting that H3K27ac precedes active transcription during ZGA. We anticipate that the method presented here could be applied to a variety of developmental processes in any model and non-model organisms.

Discoveries in biological neural networks (BNNs) shaped artificial neural networks (ANNs) and computational parallels between ANNs and BNNs have recently been discovered. However, it is unclear to what extent discoveries in ANNs can give insight into BNN function. Here, we designed and trained an ANN to perform heat gradient navigation and found striking similarities in computation and heat representation to a known zebrafish BNN. This included shared ON- and OFF-type representations of absolute temperature and rates of change. Importantly, ANN function critically relied on zebrafish-like units. We furthermore used the accessibility of the ANN to discover a new temperature-responsive cell type in the zebrafish cerebellum. Finally, constraining the ANN by the C. elegans motor repertoire retuned sensory representations indicating that our approach generalizes. Together, these results emphasize convergence of ANNs and BNNs on stereotypical representations and that ANNs form a powerful tool to understand their biological counterparts.