Unlike adult mammals, zebrafish regenerate spinal cord tissue and recover locomotor ability after a paralyzing injury. Here, we find that ependymal cells in zebrafish spinal cords produce the neurogenic factor Hb-egfa upon transection injury. Animals with hb-egfa mutations display defective swim capacity, axon crossing, and tissue bridging after spinal cord transection, associated with disrupted indicators of neuron production. Local recombinant human HB-EGF delivery alters ependymal cell cycling and tissue bridging, enhancing functional regeneration. Epigenetic profiling reveals a tissue regeneration enhancer element (TREE) linked to hb-egfa that directs gene expression in spinal cord injuries. Systemically delivered recombinant AAVs containing this zebrafish TREE target gene expression to crush injuries of neonatal, but not adult, murine spinal cords. Moreover, enhancer-based HB-EGF delivery by AAV administration improves axon densities after crush injury in neonatal cords. Our results identify Hb-egf as a neurogenic factor necessary for innate spinal cord regeneration and suggest strategies to improve spinal cord repair in mammals.

Acute trauma stimulates local repair mechanisms but can also impact structures distant from the injury, for example through the activity of circulating factors. To study the responses of remote tissues during tissue regeneration, we profiled transcriptomes of zebrafish brains after experimental cardiac damage. We found that the transcription factor gene cebpd was upregulated remotely in brain ependymal cells as well as kidney tubular cells, in addition to its local induction in epicardial cells. cebpd mutations altered both local and distant cardiac injury responses, altering the cycling of epicardial cells as well as exchange between distant fluid compartments. Genome-wide profiling and transgenesis identified a hormone-responsive enhancer near cebpd that exists in a permissive state, enabling rapid gene expression in heart, brain and kidney after cardiac injury. Deletion of this sequence selectively abolished cebpd induction in remote tissues and disrupted fluid regulation after injury, without affecting its local cardiac expression response. Our findings suggest a model to broaden gene function during regeneration in which enhancer regulatory elements define short- and long-range expression responses to injury.

Adult zebrafish possess an elevated cardiac regenerative capacity as compared with adult mammals. In the past two decades, zebrafish have provided a key model system for studying the cellular and molecular mechanisms of innate heart regeneration. The ease of genetic manipulation in zebrafish has enabled the establishment of a genetic ablation injury model in which over 60% of cardiomyocytes can be depleted, eliciting signs of heart failure. After this severe injury, adult zebrafish efficiently regenerate lost cardiomyocytes and reverse heart failure. In this chapter, we describe the methods for inducing genetic cardiomyocyte ablation in adult zebrafish, assessing cardiomyocyte proliferation, and histologically analyzing regeneration after injury.

Zebrafish regenerate heart muscle through division of pre-existing cardiomyocytes. To discover underlying regulation, we assess transcriptome datasets for dynamic gene networks during heart regeneration and identify suppression of genes associated with the transcription factor Tp53. Cardiac damage leads to fluctuation of Tp53 protein levels, concomitant with induced expression of its central negative regulator, mdm2, in regenerating cardiomyocytes. Zebrafish lacking functional Tp53 display increased indicators of cardiomyocyte proliferation during regeneration, whereas transgenic Mdm2 blockade inhibits injury-induced cardiomyocyte proliferation. Induced myocardial overexpression of the mitogenic factors Nrg1 or Vegfaa in the absence of injury also upregulates mdm2 and suppresses Tp53 levels, and tp53 mutations augment the mitogenic effects of Nrg1. mdm2 induction is spatiotemporally associated with markers of de-differentiation in injury and growth contexts, suggesting a broad role in cardiogenesis. Our findings reveal myocardial Tp53 suppression by mitogen-induced Mdm2 as a regulatory component of innate cardiac regeneration.

INTRODUCTION:Existing guidelines for surveillance after non-small-cell lung cancer (NSCLC) treatment are inconsistent and have relatively sparse supporting literature. This study characterizes detection rates of metachronous and recurrent disease during surveillance with computed tomography scans after definitive treatment of early stage NSCLC. MATERIALS AND METHODS:The incidence of metachronous and recurrent disease in patients who previously underwent complete resection via lobectomy for stage IA NSCLC at a single center from 1996 to 2010 were evaluated. A subgroup analysis was used to compare survival of patients whose initial surveillance scan was 6 ± 3 months (early) versus 12 ± 3 months (late) after lobectomy. RESULTS:Of 294 eligible patients, 49 (17%) developed recurrent disease (14 local only, 35 distant), and 45 (15%) developed new NSCLC. Recurrent disease was found at a mean of 22 ± 19 months, and new primaries were found at a mean of 52 ± 31 months after lobectomy (P < .01). Five-year survival after diagnosis of recurrent disease was significantly lower than after diagnosis of second primaries (2.3% vs. 57.5%; P < .001). In the subgroup analysis of 187 patients, both disease detection on the initial scan (2% [2/94] vs. 4% [4/93]; P = .44) and 5-year survival (early, 80.8% vs. late, 86.7%; P = .61) were not significantly different between the early (n = 94) and the late (n = 93) groups. CONCLUSION:Surveillance after lobectomy for stage IA NSCLC is useful for identifying both new primary as well as recurrent disease, but waiting to start surveillance until 12 ± 3 months after surgery is unlikely to miss clinically important findings.

While the heart regenerates poorly in mammals, efficient heart regeneration occurs in zebrafish. Studies in zebrafish have resulted in a model in which preexisting cardiomyocytes dedifferentiate and reinitiate proliferation to replace the lost myocardium. To identify which processes occur in proliferating cardiomyocytes we have used a single-cell RNA-sequencing approach. We uncovered that proliferating border zone cardiomyocytes have very distinct transcriptomes compared to the nonproliferating remote cardiomyocytes and that they resemble embryonic cardiomyocytes. Moreover, these cells have reduced expression of mitochondrial genes and reduced mitochondrial activity, while glycolysis gene expression and glucose uptake are increased, indicative for metabolic reprogramming. Furthermore, we find that the metabolic reprogramming of border zone cardiomyocytes is induced by Nrg1/ErbB2 signaling and is important for their proliferation. This mechanism is conserved in murine hearts in which cardiomyocyte proliferation is induced by activating ErbB2 signaling. Together these results demonstrate that glycolysis regulates cardiomyocyte proliferation during heart regeneration.

The capacity to regenerate damaged tissues, such as the heart, various enormously amongst species. While heart regeneration is generally very low in mammals [1][1]–[3][2], it can regenerate efficiently in certain amphibian and fish species [4][3],[5][4]. Zebrafish has been used extensively to study heart regeneration, resulting in the identification of proliferating cardiomyocytes that drive this process [5][4]–[7][5]. However, mechanisms that drive cardiomyocyte proliferation are largely unknown. Here, using a single-cell mRNA-sequencing approach, we find a transcriptionally distinct population of dedifferentiated and proliferating cardiomyocytes in regenerating zebrafish hearts. While adult cardiomyocytes are known to rely on mitochondrial oxidative phosphorylation (OXPHOS) for energy production, these proliferating cardiomyocytes show reduced mitochondrial gene expression and decreased OXPHOS activity. Strikingly, we find that genes encoding rate-limiting enzymes of the glycolysis pathway are induced in the proliferating cardiomyocytes, and inhibiting glycolysis impairs cardiomyocyte cell cycle reentry. Mechanistically, glycolytic gene expression is induced by Nrg1/Erbb2 signaling, and this is conserved in a mouse model of enhanced regeneration. Moreover, inhibiting glycolysis in murine cardiomyocytes abrogates the mitogenic effects of Nrg1/ErbB2 signaling. Together these results reveal a conserved mechanism in which cardiomyocytes undergo metabolic reprogramming by activating glycolysis, which is essential for cell cycle reentry and heart regeneration. This could ultimately help develop therapeutic interventions that promote the regenerative capacity of the mammalian heart. [1]: #ref-1 [2]: #ref-3 [3]: #ref-4 [4]: #ref-5 [5]: #ref-7

7549 Background: Guidelines for surveillance after resection of stage 1A non-small cell lung cancer (NSCLC) vary in terms of recommended modality and frequency. The purpose of this study was to assess the optimal time to start surveillance when using CT scans. Methods: All patients who underwent lobectomy from 1996 to 2010 for stage 1A NSCLC without induction or adjuvant therapy and who had CT surveillance that started within 15 months of resection were reviewed. Only patients followed for at least two years or until new or recurrent disease was discovered were included. Patients were grouped as “early CT” if their initial surveillance CT scan was 6±3 months after lobectomy and “late CT” if their initial surveillance CT scan was 12±3 months after lobectomy. Between the two groups, the incidence of new or recurrent disease on the initial CT scan was compared using Fisher’s exact test and overall survival was compared using the log-rank test. Results: During the study period, 198 patients met inclusion criteria. There were 99 cases in both the early and late CT groups. Overall, 11% of patients (21/198; 8 local only, 13 distant) had recurrent disease and 16% of patients (31/198) were found to have new primaries over their follow up period. On average, recurrent disease was found 26±19.8 months and new primaries were found 45.7±28.9 months after resection (p=0.009). For the 31 patients with new primaries, 29 (94%) received some form of local therapy; surgery was used in 21 patients (68%). Repeat surgery was used in 3 of the 8 patients with local recurrence (37.5%), though 2 of these 3 developed contralateral lung metastases within 4 years of reoperation. In the early CT group, new or recurrent disease was found on the initial surveillance scan in 2% of patients (2/99) compared to 4% of patients (4/99) in the late CT group (p=0.7). The 5-year survival from initial resection of the two groups was not significantly different. Conclusions: Both recurrent disease and new primary cancers are relatively common after lobectomy for stage 1A NSCLC, but rarely are evident on CT scan within 15 months of surgery. Waiting to starting CT scan surveillance until 9 to 15 months after surgery is unlikely to miss clinically important findings.