Bicuspid Aortic Valve: Current Therapeutic Strategies

Bicuspid aortic valve (BAV) is the most common congenital valvular pathology with an incidence of 1–2% in the general population. It is associated with an ascending aortic aneurysm phenotype in 26–50%, and aortic root (+/− ascending aneurysm) phenotype in up to 20–32% of patients. Bicuspid aortic valve patients present with a spectrum of valvular, ascending, and aortic root aneurysmal pathophysiologies. This variable spectrum has mandated the development of an array of surgical procedures to be able to tailor an individualized approach to BAV syndrome for a typically younger BAV population in which long-term outcomes are especially relevant . This chapter will delineate the current evidence-based surgical therapeutic strategies for patients with a BAV syndrome of aortic valve stenosis or insufficiency phenotype and aortic phenotype pathophysiology and include aortic valve replacement, aortic valve repair, aortic valve and supracoronary ascending aorta replacement (AVRSCAAR), Bentall procedure, and valve-sparing root reimplantation

Distinct enhancers at the Pax3 locus can function redundantly to regulate neural tube and neural crest expressions

AbstractPax3 is a transcription factor expressed in somitic mesoderm, dorsal neural tube and pre-migratory neural crest during embryonic development. We have previously identified cis-acting enhancer elements within the proximal upstream genomic region of Pax3 that are sufficient to direct functional expression of Pax3 in neural crest. These elements direct expression of a reporter gene to pre-migratory neural crest in transgenic mice, and transgenic expression of a Pax3 cDNA using these elements is sufficient to rescue neural crest development in mice otherwise lacking endogenous Pax3. We show here that deletion of these enhancer sequences by homologous recombination is insufficient to abrogate neural crest expression of Pax3 and results in viable mice. We identify a distinct enhancer in the fourth intron that is also capable of mediating neural crest expression in transgenic mice and zebrafish. Our analysis suggests the existence of functionally redundant neural crest enhancer modules for Pax3

Cardiovascular Outcomes in Aortopathy: GenTAC Registry of Genetically Triggered Aortic Aneurysms and Related Conditions.

BACKGROUND: The GenTAC (Genetically Triggered Thoracic Aortic Aneurysm and Cardiovascular Conditions) Registry enrolled patients with genetic aortopathies between 2007 and 2016. OBJECTIVES: The purpose of this study was to compare age distribution and probability of elective surgery for proximal aortic aneurysm, any dissection surgery, and cardiovascular mortality among aortopathy etiologies. METHODS: The GenTAC study had a retrospective/prospective design. Participants with bicuspid aortic valve (BAV) with aneurysm (n = 879), Marfan syndrome (MFS) (n = 861), nonsyndromic heritable thoracic aortic disease (nsHTAD) (n = 378), Turner syndrome (TS) (n = 298), vascular Ehlers-Danlos syndrome (vEDS) (n = 149), and Loeys-Dietz syndrome (LDS) (n = 121) were analyzed. RESULTS: The 25% probability of elective proximal aortic aneurysm surgery was 30 years for LDS (95% CI: 18-37 years), followed by MFS (34 years; 95% CI: 32-36 years), nsHTAD (52 years; 95% CI: 48-56 years), and BAV (55 years; 95% CI: 53-58 years). Any dissection surgery 25% probability was highest in LDS (38 years; 95% CI: 33-53 years) followed by MFS (51 years; 95% CI: 46-57 years) and nsHTAD (54 years; 95% CI: 51-61 years). BAV experienced the largest relative frequency of elective surgery to any dissection surgery (254/33 = 7.7), compared with MFS (273/112 = 2.4), LDS (35/16 = 2.2), or nsHTAD (82/76 = 1.1). With MFS as the reference population, risk of any dissection surgery or cardiovascular mortality was lowest in BAV patients (HR: 0.13; 95% CI: 0.08-0.18; HR: 0.13; 95%: CI: 0.06-0.27, respectively). The greatest risk of mortality was seen in patients with vEDS. CONCLUSIONS: Marfan and LDS cohorts demonstrate age and event profiles congruent with the current understanding of syndromic aortopathies. BAV events weigh toward elective replacement with relatively few dissection surgeries. Nonsyndromic HTAD patients experience near equal probability of dissection vs prophylactic surgery, possibly because of failure of early diagnosis

Interaction between SNAI2 and MYOD enhances oncogenesis and suppresses differentiation in Fusion Negative Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is an aggressive pediatric malignancy of the muscle, that includes Fusion Positive (FP)-RMS harboring PAX3/7-FOXO1 and Fusion Negative (FN)-RMS commonly with RAS pathway mutations. RMS express myogenic master transcription factors MYOD and MYOG yet are unable to terminally differentiate. Here, we report that SNAI2 is highly expressed in FN-RMS, is oncogenic, blocks myogenic differentiation, and promotes growth. MYOD activates SNAI2 transcription via super enhancers with striped 3D contact architecture. Genome wide chromatin binding analysis demonstrates that SNAI2 preferentially binds enhancer elements and competes with MYOD at a subset of myogenic enhancers required for terminal differentiation. SNAI2 also suppresses expression of a muscle differentiation program modulated by MYOG, MEF2, and CDKN1A. Further, RAS/MEK-signaling modulates SNAI2 levels and binding to chromatin, suggesting that the differentiation blockade by oncogenic RAS is mediated in part by SNAI2. Thus, an interplay between SNAI2, MYOD, and RAS prevents myogenic differentiation and promotes tumorigenesis. Rhabdomyosarcomas are tumours blocked in myogenic differentiation, which despite the expression of master muscle regulatory factors, including MYOD, are unable to differentiate. Here, the authors show that SNAI2 is upregulated by MYOD through super enhancers, binds to MYOD target enhancers, and arrests differentiation

MYOD-SKP2 axis boosts tumorigenesis in fusion negative rhabdomyosarcoma by preventing differentiation through p57Kip2^{Kip2} targeting

Rhabdomyosarcomas (RMS) are pediatric mesenchymal-derived malignancies encompassing PAX3/7-FOXO1 Fusion Positive (FP)-RMS, and Fusion Negative (FN)-RMS with frequent RAS pathway mutations. RMS express the master myogenic transcription factor MYOD that, whilst essential for survival, cannot support differentiation. Here we discover SKP2, an oncogenic E3-ubiquitin ligase, as a critical pro-tumorigenic driver in FN-RMS. We show that SKP2 is overexpressed in RMS through the binding of MYOD to an intronic enhancer. SKP2 in FN-RMS promotes cell cycle progression and prevents differentiation by directly targeting p27$^{Kip1}$ and p57$^{Kip2}$, respectively. SKP2 depletion unlocks a partly MYOD-dependent myogenic transcriptional program and strongly affects stemness and tumorigenic features and prevents in vivo tumor growth. These effects are mirrored by the investigational NEDDylation inhibitor MLN4924. Results demonstrate a crucial crosstalk between transcriptional and post-translational mechanisms through the MYOD-SKP2 axis that contributes to tumorigenesis in FN-RMS. Finally, NEDDylation inhibition is identified as a potential therapeutic vulnerability in FN-RMS

Abstracts from the 20th International Symposium on Signal Transduction at the Blood-Brain Barriers

https://deepblue.lib.umich.edu/bitstream/2027.42/138963/1/12987_2017_Article_71.pd

Cardiac development and the transcriptional regulation of Pax3

Transcriptional regulation of the Pax3 transcription factor in cardiac neural crest cells has not been elucidated. Pax3 is expressed in the neural crest and somite. To elucidate the cis-regulatory regions that regulate Pax3 transcription and expression during cardiac development, deletional analysis in transgenic mice identified two cis-regulatory elements. Both are required for neural crest, but not somite expression of Pax3 in transgenic mice. A yeast 1-hybrid system identified TEAD2 as a potential upstream regulator of Pax3. In-situ hybridization showed that Pax3 and TEAD2 are co-expressed by pre-migratory neural crest cells. Deletion of a consensus TEAD2 binding site in the neural crest regulatory element destroys reporter gene expression in transgenic mice. EMSA confirmed that TEAD2 and its co-activator YAP65 bind to this site. A dominant negative TEAD2-Engrailed fusion protein can down regulate activation of a reporter construct in 3T3 cells, as well as endogenous Pax3 expression in transgenic mice. To determine if these neural crest regulatory elements are required for cardiovascular development, these sequences were deleted in mice using homologous recombination. Replacement of this region with a floxed neo cassette generated expected cardiac outflow tract and neural tube defects. Unexpectedly, hypaxial muscle defects were also noted. To determine if these defects were secondary to neo cassette disruption of Pax3 expression, the neo cassette was removed using a cre recombinase transgenic mouse. Unexpectedly, removal of the floxed neo cassette generated mice with no neural crest or somite defects. Thus, replacement of the neural crest regulatory element with the floxed neo cassette generated a new allele of Pax3. This new allele was used to rescue Pax3 expression in either the neural crest or somite domain in a tissue specific manner. Therefore, two cis-regulatory elements have been identified which are sufficient, but not required for Pax3 expression in cardiac neural crest cells. A trans-acting factor, TEAD2 has been identified as a possible regulator of Pax3 transcription. And, a new allele of Pax3 has been generated which can be used as a genetic tool to rescue Pax3 expression in a tissue specific manner to delineate the transcriptional regulation of Pax3 in the cardiac neural crest