Satb1 regulates the self-renewal of hematopoietic stem cells by promoting quiescence and repressing differentiation commitment.

How hematopoietic stem cells (HSCs) coordinate the regulation of opposing cellular mechanisms such as self-renewal and differentiation commitment remains unclear. Here we identified the transcription factor and chromatin remodeler Satb1 as a critical regulator of HSC fate. HSCs lacking Satb1 had defective self-renewal, were less quiescent and showed accelerated lineage commitment, which resulted in progressive depletion of functional HSCs. The enhanced commitment was caused by less symmetric self-renewal and more symmetric differentiation divisions of Satb1-deficient HSCs. Satb1 simultaneously repressed sets of genes encoding molecules involved in HSC activation and cellular polarity, including Numb and Myc, which encode two key factors for the specification of stem-cell fate. Thus, Satb1 is a regulator that promotes HSC quiescence and represses lineage commitment.

TNF-alpha-mediated inflammation in cerebral aneurysms: a potential link to growth and rupture.

Intracranial aneurysm (IA) rupture is one of the leading causes of stroke in the United States and remains a major health concern today. Most aneurysms are asymptomatic with a minor percentage of rupture annually. Regardless, IA rupture has a devastatingly high mortality rate and does not have specific drugs that stabilize or prevent aneurysm rupture, though other preventive therapeutic options such as clipping and coiling of incidental aneurysms are available to clinicians. The lack of specific drugs to limit aneurysm growth and rupture is, in part, attributed to the limited knowledge on the biology of IA growth and rupture. Though inflammatory macrophages and lymphocytes infiltrate the aneurysm wall, a link between their presence and aneurysm growth with subsequent rupture is not completely understood. Given our published results that demonstrate that the pro-inflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), is highly expressed in human ruptured aneurysms, we hypothesize that pro-inflammatory cell types are the prime source of TNF-alpha that initiate damage to endothelium, smooth muscle cells (SMC) and internal elastic lamina (IEL). To gain insights into TNF-alpha expression in the aneurysm wall, we have examined the potential regulators of TNF-alpha and report that higher TNF-alpha expression correlates with increased expression of intracellular calcium release channels that regulate intracellular calcium (Ca2+), and Toll like receptors (TLR) that mediate innate immunity. Moreover, the reduction of tissue inhibitor of metalloproteinase-1 (TIMP-1) expression provides insights on why higher matrix metalloproteinase (MMP) activity is noted in ruptured IA. Because TNF-alpha is known to amplify several signaling pathways leading to inflammation, apoptosis and tissue degradation, we will review the potential role of TNF-alpha in IA formation, growth and rupture. Neutralizing TNF-alpha action in the aneurysm wall may have a beneficial effect in preventing aneurysm growth by reducing inflammation and arterial remodeling.

Minimal PU.1 reduction induces a preleukemic state and promotes development of acute myeloid leukemia.

Modest transcriptional changes caused by genetic or epigenetic mechanisms are frequent in human cancer. Although loss or near-complete loss of the hematopoietic transcription factor PU.1 induces acute myeloid leukemia (AML) in mice, a similar degree of PU.1 impairment is exceedingly rare in human AML; yet, moderate PU.1 inhibition is common in AML patients. We assessed functional consequences of modest reductions in PU.1 expression on leukemia development in mice harboring DNA lesions resembling those acquired during human stem cell aging. Heterozygous deletion of an enhancer of PU.1, which resulted in a 35% reduction of PU.1 expression, was sufficient to induce myeloid-biased preleukemic stem cells and their subsequent transformation to AML in a DNA mismatch repair-deficient background. AML progression was mediated by inhibition of expression of a PU.1-cooperating transcription factor, Irf8. Notably, we found marked molecular similarities between the disease in these mice and human myelodysplastic syndrome and AML. This study demonstrates that minimal reduction of a key lineage-specific transcription factor, which commonly occurs in human disease, is sufficient to initiate cancer development, and it provides mechanistic insight into the formation and progression of preleukemic stem cells in AML.

Analysis of the techniques for thoracic- and lumbar-level localization during posterior spine surgery and the occurrence of wrong-level surgery: results from a national survey.

BACKGROUND CONTEXT: Despite the frequency with which surgeons perform posterior spinal surgery and the precautions against wrong-site surgery, operations on incorrect levels still occur. Wrong-level exposure is documented in 0.32% to 15% of cases. Additionally, there is little consensus as to what is the most accurate method for localizing the correct spinal level. PURPOSE: The purpose of this study is to investigate the most commonly used localization methods and their association with wrong-level surgery, to determine the prevalence of wrong-level localization, and to identify circumstances commonly associated with wrong-level surgery, and to offer recommendations that may reduce the incidence of these errors. STUDY DESIGN/SETTING: This was an online survey study that was distributed to North American Spine Society (NASS) members (including both orthopedic surgeons and neurosurgeons). The survey was sent as a Web link within an e-mail. PATIENT SAMPLE: A total of 2,338 surgeons received the survey, 532 opened the survey, and 173 completed it (7.4% response rate). The survey was only sent once, as recommended by NASS. Of those that responded, 72% (124 of 173) were orthopedic surgeons, 28% (49 of 173) were neurosurgeons, and 73% (126 of 173) were spine fellowship trained. OUTCOME MEASURES: We sought to investigate self-reported localization methods that are most commonly used (both anatomic landmarks and imaging techniques), the prevalence of wrong-level surgery, and any correlations between localization method and wrong-level surgery. METHODS: An eight-question anonymous survey was distributed to members of NASS, including orthopedic surgeons and neurosurgeons. There was no pilot testing or validation performed for this survey. The survey was sent as a Web link within an e-mail. Some questions asked surgeons to select as many responses as applicable, and others allowed surgeons to describe in detail any cases of wrong-level surgery. This study neither requires nor receives funding; additionally, no conflicts of interests were reported. RESULTS: Fluoroscopy was the most commonly used imaging technique for thoracic and lumbar surgeries (89% and 86%, respectively), followed by plain radiographs (54% and 58%, respectively). Surgeons were allowed to select as many responses as applicable, and 76 surgeons reported using both plain radiographs and fluoroscopy. The facet joint with corresponding pedicle was the most commonly used anatomic landmark for localization of thoracic and lumbar surgeries (67% and 59%, respectively), followed by the spinous process (49% and 52%, respectively). Sixty-eight percent of surgeons admitted to wrong-level localization, some of which were rectified intraoperatively, during their careers. Fifty-six percent of these surgeons reported using plain radiographs and 44% used fluoroscopy when the errors occurred. Common sources of preoperative errors included failure to visualize known reference points, recognize unconventional spinal anatomy, and adequately visualize the level because of large body habitus. Common sources of intraoperative errors included poor communication, failure to relocalize after exposure, and poor counting methods. CONCLUSIONS: Despite the variety of localization modalities, most surgeons use only a few. Whereas wrong-level localization is relatively rare, the ideal frequency is never. There is no standard approach that will entirely eliminate these mistakes; however, using a localization time out and increasing awareness of common sources of error may help decrease the incidence of wrong-level spine surgery.

Understanding acute apophyseal spinous process avulsion injuries.

Apophyseal spinous process avulsion injury was first described in 1941. Since then, there have been sparse additional reports in the literature. The authors report their second case, involving an elite adolescent tennis player. The patient underwent surgical excision of the avulsed spinous process 12 weeks after initial presentation and experienced complete resolution of back pain. The authors provide the first reported histopathological analysis of the avulsion fracture site in the literature for both of their cases. The avulsion injury of the interspinous ligament was characterized by hypercellular fibrocartilage tissue, similar to that seen in severe Osgood-Schlatter's disease. The key physical examination finding in patients with avulsion spinous process fractures is acute tenderness directly over the fracture site that worsens with flexion rather than extension (unlike in spondylolysis). Patients should have routine radiographs, including dynamic flexion-extension views, magnetic resonance imaging, and computed tomography. The authors conclude that after 6 months of nonsurgical management for an athlete, surgical excision should be offered as an alternative. In both of their cases, nonsurgical management failed. Surgical excision offers definitive and simple treatment, as well as early return to athletic activities. Both patients were allowed to return to their competitive level of performance 6 weeks after surgery.

Detrimental effects of discectomy on intervertebral disc biology can be decelerated by growth factor treatment during surgery: a large animal organ culture model.

BACKGROUND CONTEXT: Lumbar discectomies are common surgical interventions that treat radiculopathy by removing herniated and loose intervertebral disc (IVD) tissues. However, remaining IVD tissue can continue to degenerate resulting in long-term clinical problems. Little information is available on the effects of discectomy on IVD biology. Currently, no treatments exist that can suspend or reverse the degeneration of the remaining IVD. PURPOSE: To improve the knowledge on how discectomy procedures influence IVD physiology and to assess the potential of growth factor treatment as an augmentation during surgery. STUDY DESIGN: To determine effects of discectomy on IVDs with and without transforming growth factor beta 3 (TGFß3) augmentation using bovine IVD organ culture. METHODS: This study determined effects of discectomy with and without TGFß3 injection using 1-, 6-, and 19-day organ culture experiments. Treated IVDs were injected with 0.2 µg TGFß3 in 20 µL phosphate-buffered saline+bovine serum albumin into several locations of the discectomy site. Cell viability, gene expression, nitric oxide (NO) release, IVD height, aggrecan degradation, and proteoglycan content were determined. RESULTS: Discectomy significantly increased cell death, aggrecan degradation, and NO release in healthy IVDs. Transforming growth factor beta 3 injection treatment prevented or mitigated these effects for the 19-day culture period. CONCLUSIONS: Discectomy procedures induced cell death, catabolism, and NO production in healthy IVDs, and we conclude that post-discectomy degeneration is likely to be associated with cell death and matrix degradation. Transforming growth factor beta 3 injection augmented discectomy procedures by acting to protect IVD tissues by maintaining cell viability, limiting matrix degradation, and suppressing NO. We conclude that discectomy procedures can be improved with injectable therapies at the time of surgery although further in vivo and human studies are required.

Genetic polymorphisms associated with intervertebral disc degeneration.

BACKGROUND CONTEXT: Disc degeneration (DD) is a multifaceted chronic process that alters the structure and function of the intervertebral discs and can lead to painful conditions. The pathophysiology of degeneration is not well understood, but previous studies suggest that certain genetic polymorphisms may be important contributing factors leading to an increased risk of DD. PURPOSE: To review the genetic factors in DD with a focus on polymorphisms and their putative role in the pathophysiology of degeneration. Elucidating the genetic components that are associated with degeneration could provide insights into the mechanism of the process. Furthermore, defining these relationships and eventually using them in a clinical setting may allow an identification and early intervention for those who are at a high risk for painful DD. STUDY DESIGN: Literature review. METHODS: This literature review focused on the studies concerning genetic polymorphisms and their associations with DD. RESULTS: Genetic polymorphisms in 20 genes have been analyzed in association with DD, including vitamin D receptor, growth differentiation factor 5 (GDF5), aggrecan, collagen Types I, IX, and XI, fibronectin, hyaluronan and proteoglycan link protein 1 (HAPLN1), thrombospondin, cartilage intermediate layer protein (CILP), asporin, MMP1, 2, and 3, parkinson protein 2, E3 ubiquitin protein ligase (PARK2), proteosome subunit ß type 9 (PSMB9), tissue inhibitor of metalloproteinase (TIMP), cyclooxygenase-2 (COX2), and IL1α, IL1ß, and IL6. Each genetic polymorphism codes for a protein that has a functional role in the pathogenesis of DD. CONCLUSIONS: There are known associations between several genetic polymorphisms and DD. Of the 20 genes analyzed, polymorphisms in vitamin D receptor, aggrecan, Type IX collagen, asporin, MMP3, IL1, and IL6 show the most promise as functional variants. Genetic studies are crucial for understanding the mechanism of the degeneration. This genetic information could eventually be used as a predictive model for determining a patient's risk for symptomatic DD.

The interindividual variation in femoral neck width is associated with the acquisition of predictable sets of morphological and tissue-quality traits and differential bone loss patterns.

A better understanding of femoral neck structure and age-related bone loss will benefit research aimed at reducing fracture risk. We used the natural variation in robustness (bone width relative to length) to analyze how adaptive processes covary traits in association with robustness, and whether the variation in robustness affects age-related bone loss patterns. Femoral necks from 49 female cadavers (29-93 years of age) were evaluated for morphological and tissue-level traits using radiography, peripheral quantitative computed tomography, micro-computed tomography, and ash-content analysis. Femoral neck robustness was normally distributed and varied widely with a coefficient of variation of 14.9%. Age-adjusted partial regression analysis revealed significant negative correlations (p < 0.05) between robustness and relative cortical area, cortical tissue-mineral density (Ct.TMD), and trabecular bone mineral density (Ma.BMD). Path analysis confirmed these results showing that a one standard deviation (SD) increase in robustness was associated with a 0.70 SD decrease in RCA, 0.47 SD decrease in Ct.TMD, and 0.43 SD decrease in Ma.BMD. Significantly different bone loss patterns were observed when comparing the most slender and most robust tertiles. Robust femora showed significant negative correlations with age for cortical area (R(2) = 0.29, p < 0.03), Ma.BMD (R(2) = 0.34, p < 0.01), and Ct.TMD (R(2) = 0.4, p < 0.003). However, slender femora did not show these age-related changes (R(2) < 0.09, p > 0.2). The results indicated that slender femora were constructed with a different set of traits compared to robust femora, and that the natural variation in robustness was a determinant of age-related bone loss patterns. Clinical diagnoses and treatments may benefit from a better understanding of these robustness-specific structural and aging patterns.

Tumor necrosis factor alpha is a key modulator of inflammation in cerebral aneurysms.

OBJECTIVE: Although intracranial aneurysms (IAs) are a major public health problem in the United States, few etiological factors are known. Most aneurysms remain asymptomatic until they rupture, producing subarachnoid hemorrhage, one of the most severe forms of stroke. Despite the technical advances in endovascular and microsurgical treatment, these patients still have high mortality and morbidity rates. Hence, the biology of aneurysm formation and growth is of intense interest. The presence of T and B lymphocytes, as well as macrophages, in human IA tissues suggests a role for inflammation in IA pathogenesis. However, the types of cytokines that are involved and regulated during cerebral aneurysm formation and growth are not known. To study the underlying pathogenesis of IA, we analyzed the expression of cytokines that participate in proinflammatory and anti-inflammatory responses. METHODS: Polymerase chain reaction was used to assess relative messenger ribonucleic acid expression levels of cytokines and an apoptotic modulator, Fas-associated death domain protein. Western blot analysis was used to determine protein expression from these genes. RESULTS: We show that the proinflammatory cytokine, tumor necrosis factor alpha and its proapoptotic downstream target, Fas-associated death domain protein, are increased in human aneurysms. In contrast, interleukin 10, which is secreted predominantly by T helper 2 cells, was absent in aneurysms. Polymerase chain reaction-derived gene expression data were confirmed by Western blotting using specific antibodies. CONCLUSION: Increased tumor necrosis factor alpha and Fas-associated death domain protein may have deleterious primary and secondary effects on cerebral arteries by promoting inflammation and subsequent apoptosis in vascular and immune cells, thereby weakening vessel walls.