A Multifaceted Research Engagement Program Improved the Academic Productivity of General Surgery Residents

OBJECTIVE

Surgeon-scientists are becoming increasingly scarce, and therefore, engaging residents in research during their training is important. We evaluated whether a multifaceted research engagement program was associated with increased academic productivity of general surgery residents.

DESIGN

Our research engagement program has 4 pillars: A research requirement, a structured research curriculum, infrastructure to support residents' research, and an annual resident research day to highlight trainees' work. We compared the number of manuscripts published per chief resident during the 4 years before and after program implementation in 2013. We performed subgroup analyses to examine productivity of research track residents and clinical track residents.

SETTING

A general surgery residency program in an academic setting.

PARTICIPANTS

The participants were 57 general surgery residents (23 research track and 34 clinical track) graduating between 2010 and 2017.

RESULTS

There was a significant increase in overall research productivity, with 28 chief residents publishing an average of 2.3 ± 1.0 manuscripts before and 29 chief residents publishing an average of 8.5 ± 3.2 manuscripts after program implementation (p = 0.01). Research track residents had a nonsignificant increase in publications from an average of 6.3 ± 3.1 before to 15.4 ± 8.9 after the new program (p = 0.10). Clinical track residents had a significant increase in publications from a median of 0.9 (interquartile range: 0.5, 1.0) before to a median of 1.3 (interquartile range: 1.2, 8.6) after the new program (p = 0.03).

CONCLUSIONS

Implementation of a multifaceted research engagement program was associated with a significant increase in manuscripts published by general surgery residents, including clinical track residents. Components of our program may be of use to other programs looking to improve resident research engagement and productivity.

Elastin-Specific Autoimmunity in Smokers With Thoracic Aortic Aneurysm and Dissection is Independent of Chronic Obstructive Pulmonary Disease

Background Thoracic aortic aneurysm ( TAA ) and dissection ( TAD ) are characterized by progressive disorganization of the aortic wall matrix, including elastin, a highly immunogenic molecule. Whether acquired autoimmune responses can be detected in TAA / TAD patients who are smokers is unknown. The objectives of this study were to determine whether TAA / TAD smokers have increased T-cell responses to human elastin fragments, and to determine whether autoimmune responses in TAA / TAD smokers are dependent on chronic obstructive pulmonary disease. Methods and Results In a cross-sectional study (N=86), we examined peripheral blood CD 4⁺ T cell responses to elastin fragments in never-, former-, or current-smokers with or without TAA / TAD . CD 4⁺ T cells were co-cultured with irradiated autologous peripheral blood CD 1a⁺/ CD 14⁺ antigen presenting cells pulsed with or without elastin fragments to measure cytokine production. Baseline plasma concentration of anti-elastin antibodies and elastin-degrading enzymes (eg, matrix metalloproteinase-9, and -12, and neutrophil elastase) were measured in the same cohort. elastin fragment-specific CD 4⁺ T cell expression of interferon-γ, and anti-elastin antibodies were dependent on history of smoking in TAA / TAD patients but were independent of chronic obstructive pulmonary disease. Matrix metalloproteinase-9, and -12, and neutrophil elastase plasma concentrations were also significantly elevated in ever-smokers with TAA / TAD . Conclusions Cigarette smoke is associated with loss of self-tolerance and induction of elastin-specific autoreactive T- and B-cell responses in patients with TAA / TAD . Development of peripheral blood biomarkers to track immunity to self-antigens could be used to identify and potentially prognosticate susceptibility to TAA / TAD in smokers.

Targeting the NLRP3 Inflammasome With Inhibitor MCC950 Prevents Aortic Aneurysms and Dissections in Mice

Background

Aortic aneurysms and dissections are highly lethal diseases for which an effective treatment strategy is critically needed to prevent disease progression. The nucleotide‐binding oligomerization domain–like receptor pyrin domain containing 3 (NLRP3)–caspase‐1 inflammasome cascade was recently shown to play an important role in aortic destruction and disease development. In this study, we tested the effects of MCC950, a potent, selective NLRP3 inhibitor, on preventing aortic destruction and aortic aneurysm and dissection formation.

Methods and Results

In a model of sporadic aortic aneurysm and dissection induced by challenging wild‐type mice with a high‐fat, high‐cholesterol diet and angiotensin II infusion, MCC950 treatment significantly inhibited challenge‐induced aortic dilatation, dissection, and rupture in different thoracic and abdominal aortic segments in both male and female mice. Aortic disease reduction by MCC950 was associated with the prevention of NLRP3–caspase‐1 upregulation, smooth muscle cell contractile protein degradation, aortic cell death, and extracellular matrix destruction. Further investigation revealed that preventing matrix metallopeptidase 9 (MMP‐9) expression and activation in macrophages is an important mechanism underlying MCC950's protective effect. We found that caspase‐1 directly activated MMP‐9 by cleaving its N‐terminal inhibitory domain. Moreover, the genetic knockdown of Nlrp3 or Casp‐1 in mice or treatment of mice with MCC950 diminished the challenge‐induced N‐terminal cleavage of MMP‐9, MMP‐9 activation, and aortic destruction.

Conclusions

Our findings suggest that the NLRP3–caspase‐1 inflammasome directly activates MMP‐9. Targeting the inflammasome with MCC950 is a promising approach for preventing aortic destruction and aortic aneurysm and dissection development.

Aortic Aneurysms and Dissections Series: Part II: Dynamic Signaling Responses in Aortic Aneurysms and Dissections

Aortic structure and function are controlled by the coordinated actions of different aortic cells and the extracellular matrix. Several pathways have been identified that control the aortic wall in a cell-type-specific manner and play diverse roles in various phases of aortic injury, repair, and remodeling. This complexity of signaling in the aortic wall poses challenges to the development of therapeutic strategies for treating aortic aneurysms and dissections. Here, in part II of this Recent Highlights series on aortic aneurysms and dissections, we will summarize recent studies published in Arteriosclerosis, Thrombosis, and Vascular Biology that have contributed to our knowledge of the signaling pathway-related mechanisms of aortic aneurysms and dissections.

Aortic Aneurysms and Dissections Series

The aortic wall is composed of highly dynamic cell populations and extracellular matrix. In response to changes in the biomechanical environment, aortic cells and extracellular matrix modulate their structure and functions to increase aortic wall strength and meet the hemodynamic demand. Compromise in the structural and functional integrity of aortic components leads to aortic degeneration, biomechanical failure, and the development of aortic aneurysms and dissections (AAD). A better understanding of the molecular pathogenesis of AAD will facilitate the development of effective medications to treat these conditions. Here, we summarize recent findings on AAD published in ATVB. In this issue, we focus on the dynamics of aortic cells and extracellular matrix in AAD; in the next issue, we will focus on the role of signaling pathways in AAD.

Spinal cord deficit after 1114 extent II open thoracoabdominal aortic aneurysm repairs

OBJECTIVE

Crawford extent II repairs are the most extensive thoracoabdominal aortic aneurysm operations and pose the greatest risk of postoperative spinal cord deficit. We sought to examine spinal cord deficit after open extent II thoracoabdominal aortic aneurysm repair to identify predictors of the most serious type: persistent paraplegia or paraparesis.

METHODS

We included 1114 extent II thoracoabdominal aortic aneurysm repairs performed from 1991 to 2017. Intercostal/lumbar artery reattachment (n = 959, 86.1%) and cerebrospinal fluid drainage (n = 698, 62.7%) were used to mitigate the risk of postoperative spinal cord deficit. We used univariate and multivariable analyses to examine spinal cord deficit and identify predictors of persistent paraplegia or paraparesis, defined as paraplegia or paraparesis present at the time of early death or hospital discharge.

RESULTS

Spinal cord deficit developed after 151 (13.6%) repairs: 86 (7.7%) cases of persistent paraplegia or paraparesis (51 paraplegia; 35 paraparesis) and 65 (6.1%) cases of transient paraplegia or paraparesis. Patients with spinal cord deficit were older (median 68 vs 65 years, P < .001) and had more rupture (6.6% vs 2.2%, P = .002) and urgent/emergency repair (25.2% vs 16.9%, P = .01) than those without. Persistent paraplegia or paraparesis developed immediately in 47 patients (4.2%) and was delayed in 39 patients (3.5%). Urgent/emergency repair (relative risk ratio, 2.31; P = .002), coronary artery disease (relative risk ratio, 1.80, P = .01), and chronic symptoms (relative risk ratio, 1.76, P = .02) independently predicted persistent paraplegia or paraparesis. Reattaching intercostal/lumbar arteries (relative risk ratio, 0.38, P < .001) and heritable disease (relative risk ratio, 0.36, P = .01) were protective. Early and late survival were poorer in those with persistent paraplegia or paraparesis than in those without.

CONCLUSIONS

Spinal cord deficit after extent II thoracoabdominal aortic aneurysm repairs remains concerning; survival is worse in patients with persistent paraplegia or paraparesis. The complexity of spinal cord deficit and persistent paraplegia or paraparesis warrant further study.

Critical Role of Cytosolic DNA and Its Sensing Adaptor STING in Aortic Degeneration, Dissection, and Rupture

BACKGROUND

Sporadic aortic aneurysm and dissection (AAD), caused by progressive aortic smooth muscle cell (SMC) loss and extracellular matrix degradation, is a highly lethal condition. Identifying mechanisms that drive aortic degeneration is a crucial step in developing an effective pharmacologic treatment to prevent disease progression. Recent evidence has indicated that cytosolic DNA and abnormal activation of the cytosolic DNA sensing adaptor STING (stimulator of interferon genes) play a critical role in vascular inflammation and destruction. Here, we examined the involvement of this mechanism in aortic degeneration and sporadic AAD formation.

METHODS

The presence of cytosolic DNA in aortic cells and activation of the STING pathway were examined in aortic tissues from patients with sporadic ascending thoracic AAD. The role of STING in AAD development was evaluated in Sting-deficient (Sting^gt/gt) mice in a sporadic AAD model induced by challenging mice with a combination of a high-fat diet and angiotensin II. We also examined the direct effects of STING on SMC death and macrophage activation in vitro.

RESULTS

In human sporadic AAD tissues, we observed the presence of cytosolic DNA in SMCs and macrophages and significant activation of the STING pathway. In the sporadic AAD model, Sting^gt/gt mice showed significant reductions in challenge-induced aortic enlargement, dissection, and rupture in both the thoracic and abdominal aortic regions. Single-cell transcriptome analysis revealed that aortic challenge in wild-type mice induced the DNA damage response, the inflammatory response, dedifferentiation and cell death in SMCs, and matrix metalloproteinase expression in macrophages. These changes were attenuated in challenged Sting^gt/gt mice. Mechanistically, nuclear and mitochondrial DNA damage in SMCs and the subsequent leak of DNA to the cytosol activated STING signaling, which induced cell death through apoptosis and necroptosis. In addition, DNA from damaged SMCs was engulfed by macrophages in which it activated STING and its target interferon regulatory factor 3, which directly induced matrix metalloproteinase-9 expression. We also found that pharmacologically inhibiting STING activation partially prevented AAD development.

CONCLUSIONS

Our findings indicate that the presence of cytosolic DNA and subsequent activation of cytosolic DNA sensing adaptor STING signaling represent a key mechanism in aortic degeneration and that targeting STING may prevent sporadic AAD development.

ECMO for Acute Respiratory Distress Syndrome After Thoracoabdominal Aortic Aneurysm Repair

Acute respiratory distress syndrome (ARDS) after thoracoabdominal aortic aneurysm (TAAA) repair poses a formidable challenge. Despite conventional maneuvers in the operating room, perioperative ARDS may require extracorporeal membrane oxygenation (ECMO). We present three cases of successful ECMO for ARDS after TAAA repair and discuss management of anticoagulation and cerebrospinal fluid drains. Our experience suggests that ECMO is reasonable in selected patients after TAAA repair.

Activation of Bone Marrow-Derived Cells and Resident Aortic Cells During Aortic Injury

BACKGROUND

The process of aortic injury, repair, and remodeling during aortic aneurysm and dissection is poorly understood. We examined the activation of bone marrow (BM)-derived and resident aortic cells in response to aortic injury in a mouse model of sporadic aortic aneurysm and dissection.

MATERIALS AND METHODS

Wild-type C57BL/6 mice were transplanted with green fluorescent protein (GFP)+ BM cells. For 4 wk, these mice were either unchallenged with chow diet and saline infusion or challenged with high-fat diet and angiotensin II infusion. We then examined the aortic recruitment of GFP+ BM-derived cells, growth factor production, and the differentiation potential of GFP+ BM-derived and GFP- resident aortic cells.

RESULTS

Aortic challenge induced recruitment of GFP+ BM cells and activation of GFP- resident aortic cells, both of which produced growth factors. Although BM cells and resident aortic cells equally contributed to the fibroblast populations, we did not detect the differentiation of BM cells into smooth muscle cells. Interestingly, aortic macrophages were both of BM-derived (45%) and of non-BM-derived (55%) origin. We also observed a significant increase in stem cell antigen-1 (Sca-1)+ stem/progenitor cells and neural/glial antigen 2 (NG2+) cells in the aortic wall of challenged mice. Although some of the Sca-1+ cells and NG2+ cells were BM derived, most of these cells were resident aortic cells. Sca-1+ cells produced growth factors and differentiated into fibroblasts and NG2+ cells.

CONCLUSIONS

BM-derived and resident aortic cells are activated in response to aortic injury and contribute to aortic inflammation, repair, and remodeling by producing growth factors and differentiating into fibroblasts and inflammatory cells.

SMAD4 rare variants in individuals and families with thoracic aortic aneurysms and dissections

SMAD4 pathogenic variants cause juvenile polyposis (JPS) and hereditary hemorrhagic telangiectasia (HHT), and 40% of affected individuals also have thoracic aortic disease. At the same time, SMAD4 pathogenic variants have not been reported in thoracic aortic disease families without JPS-HHT. A SMAD4 heterozygous variant, c.290G>T, p.(Arg97Leu), not present in population databases and predicted to be damaging to protein function, was identified in a family with thoracic aortic disease and no evidence of HHT or JPS. Cellular studies revealed that the SMAD4 p.(Arg97Leu) alteration increased SMAD4 ubiquitination and 26S proteasome-mediated protein degradation. Smooth muscle cells (SMCs) infected with lentivirus expressing the SMAD4 p.(Arg97Leu) variant demonstrated reduced contractile protein gene expression when compared to that of wild-type SMAD4. In addition, two rare variants were identified in individuals with early age of onset of thoracic aortic dissection. These results suggest that SMAD4 rare missense variants can lead to thoracic aortic disease in individuals who do not have JPS or HHT.

Enhanced Cardiomyocyte NLRP3 Inflammasome Signaling Promotes Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is frequently associated with enhanced inflammatory response. The NLRP3 (NACHT, LRR, and PYD domain containing protein 3) inflammasome mediates caspase-1 activation and interleukin-1β release in immune cells but is not known to play a role in cardiomyocytes (CMs). Here, we assessed the role of CM NLRP3 inflammasome in AF.

METHODS

NLRP3 inflammasome activation was assessed by immunoblot in atrial whole-tissue lysates and CMs from patients with paroxysmal AF or long-standing persistent (chronic) AF. To determine whether CM-specific activation of NLPR3 is sufficient to promote AF, a CM-specific knockin mouse model expressing constitutively active NLRP3 (CM-KI) was established. In vivo electrophysiology was used to assess atrial arrhythmia vulnerability. To evaluate the mechanism of AF, electric activation pattern, Ca2+ spark frequency, atrial effective refractory period, and morphology of atria were evaluated in CM-KI mice and wild-type littermates.

RESULTS

NLRP3 inflammasome activity was increased in the atrial CMs of patients with paroxysmal AF and chronic AF. CM-KI mice developed spontaneous premature atrial contractions and inducible AF, which was attenuated by a specific NLRP3 inflammasome inhibitor, MCC950. CM-KI mice exhibited ectopic activity, abnormal sarcoplasmic reticulum Ca2+ release, atrial effective refractory period shortening, and atrial hypertrophy. Adeno-associated virus subtype-9-mediated CM-specific knockdown of Nlrp3 suppressed AF development in CM-KI mice. Finally, genetic inhibition of Nlrp3 prevented AF development in CREM transgenic mice, a well-characterized mouse model of spontaneous AF.

CONCLUSIONS

Our study establishes a novel pathophysiological role for CM NLRP3 inflammasome signaling, with a mechanistic link to the pathogenesis of AF, and establishes the inhibition of NLRP3 as a potential novel AF therapy approach.