Transmembrane signaling mechanisms are critical for regulating the plasticity of neuronal connections underlying the establishment of long-lasting memory (e.g., Linden and Routtenberg, 1989, Brain Res Rev. 14: 279–296; Sossin, 1996, Trends Neurosci 19: 215–218; Mayr and Montminy, 2001, Nat Rev Mol Cell Biol. 2: 599–609; Chen et al., 2011, Nature 469: 491–497). One signaling mechanism that has received surprisingly little attention in this regard is the well-known Wnt transmembrane signaling pathway even though this pathway in the adult plays a significant role, for example, in postsynaptic dendritic spine morphogenesis and presynaptic terminal neurotransmitter release (Inestrosa and Arenas, 2010, Nature Rev Neurosci 11: 77–86). The present report now provides the first evidence of Wnt signaling in spatial information storage processes. Importantly, this Wnt participation is specific and selective. Thus, spatial, but not cued, learning in a water maze selectively elevates the levels in hippocampus of Wnt 7 and Wnt 5a, but not the Wnt 3 isoform, indicating behavioral selectivity and isoform specificity. Wnt 7 elevation is subfield-specific: granule cells show an increase with no detectable change in CA3 neurons. Wnt 7 elevation is temporally specific: increased Wnt signaling is not observed during training, but is seen 7 days and, unexpectedly, 30 days later. If the Wnt elevation after learning is activity-dependent, then it may be possible to model this effect in primary hippocampal neurons in culture. Here we evaluate the consequence of potassium or glutamate depolarization on Wnt signaling. This represents, to our knowledge, the first demonstration of an activation-dependent elevation of Wnt levels. Additionally, the novel finding emerged of an increased number of Wnt-stained puncta in neuritis suggestive of trafficking from the cell body to neuronal processes, probably dendrites. It is proposed that Wnt signaling pathways, both canonical and non-canonical, regulate long-term information storage in a behavioral-, cellular- and isoform-specific manner.

BACKGROUND: Vertebroplasty and kyphoplasty are leading treatments for patients with vertebral body compression fractures. Although cement augmentation has been shown to help relieve pain and instability from fractures containing a cleft, there is some controversy in the literature regarding the procedure’s efficacy in these cases. Additionally, some of the literature blurs the distinction between clefts and cement patterns (including cement nonunion and cement fill pattern). Both clefts and cement patterns have been mentioned in the literature as risks for poorer outcomes following cement augmentation, which can result in complications such as cement migration. OBJECTIVES: This study aims to identify the prevalence of fracture clefts and cement nonunion, the relationship between them as well as to cement fill pattern, and their association with demographics and other variables related to technique and outcomes. STUDY DESIGN: Retrospective cohort study. SETTING: Interventional radiology department at a single site university hospital. METHODS: This retrospective cohort study assessed 295 vertebroplasties/kyphoplasties performed at the University of Colorado Hospital from 2008 to 2018. Vertebral fracture cleft and cement nonunion were the main variables of interest. Presence and characterization of a fracture cleft was determined on pre-procedural imaging, defined as an air or fluid filled cavity within the fractured vertebral body on magnetic resonance or computed tomography. Cement nonunion was evaluated on post-procedural imaging, defined as air or fluid surrounding the cement bolus on magnetic resonance or computed tomography or imaging evidence of cement migration. Cement fill pattern was assessed on procedural and/or post-procedural imaging. Pain improvement scores were based on a visual analog score immediately prior to the procedure and during clinical visits in the short-term follow-up period. Additional patient demographics, medical history, and procedure details were obtained from electronic medical chart review. RESULTS: Pre-procedural vertebral fracture clefts were demonstrated in 29.8% of our cases. Increasing age, secondary osteoporosis, and thoracolumbar junction location were associated with increased odds of clefts. There was no significant difference in pain improvement outcomes in patients following cement augmentation between clefted and non-clefted compression fractures. Clefts, especially large clefts, and cleft-only fill pattern were associated with increased odds of cement nonunion. Procedure techniques (vertebroplasty, curette, and balloon kyphoplasty) demonstrated similar proportion of cement nonunion and distribution of cement fill pattern. LIMITATIONS: Cement nonunion was observed in only 6.8% of cases. Due to this low proportion, statistical inference tends to have low power. Multiple levels were treated in nearly half of the study’s patients undergoing a single vertebroplasty/kyphoplasty session; in these cases, each level was treated as independent rather than spatially correlated within the same study patient. CONCLUSIONS: Vertebral body fracture clefts are not uncommon and are related to (but distinct from) cement nonunion and cement fill patterns. Our study shows that, although patients with clefts will benefit from cement augmentation just as much as patients without a cleft, the performing provider should take note of cement fill and take extra steps to ensure optimal cement fill. These providers should also identify cement nonunion and associated complications (such as cement migration) on follow-up imaging. KEY WORDS: Kyphoplasty, vertebroplasty, compression fracture, cement nonunion, vertebral fracture cleft, spine, cement augmentation

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1267 c-Kit, the cytokine receptor that mediates SCF-induced cell proliferation, has recently been found to trigger cell polarity establishment in mouse HSPC. SCF stimulation of cultured bone marrow cells induces polarization of c-Kit and the aPKC-Par6-Par3 cell polarity machinery to one pole, followed by asymmetric division into dissimilar daughter cells. The SCF-induced redistribution of proteins in HSPC resembles that of polarized epithelial cells, in which cell surface proteins selectively traffic to either an apical or basolateral domain. We hypothesize that c-Kit might behave like an “apical” protein in this context. To test this hypothesis, we retrovirally transduced c-Kit constructs into Madin-Darby Canine Kidney (MDCK) cells, an epithelial cell line that forms polarized cysts when cultured in collagen gel. Each polarized MDCK cyst forms an apical surface facing inside, and a basolateral surface facing outside. When expressed in these cysts, a wild-type c-Kit construct traveled only to the apical surface and never to the basolateral surface, in agreement with our hypothesis. We next examined the distribution of c-Kit-BL, a c-Kit mutant that contained in its cytoplasmic domain a basolateral-trafficking (BL) signal sequence derived from TGFβ receptor. The c-Kit-BL mutant lost its apical trafficking preference and distributed instead to the BL surface, suggesting that the apical distribution of c-Kit could be blocked by an aberrant trafficking signal. We then examined the distribution of c-Kit expressed in MDCK cells cultured in liquid suspension. Under this condition, MDCK cells aggregated to form inside-out spheres, with an apical outer surface and a BL inner surface. Along with the polarity reversal of the spheres, the distribution patterns of c-Kit and c-Kit-BL were also reversed. Embedding the inside-out spheres in collagen gel re-established the original polarity, and the c-Kit constructs regained their original distributions. We then tested the behavior of c-Kit-BL-A531G and c-Kit-BL-Q532A, revertant and pseudo-revertant of c-Kit-BL, in which a critical residue (A531G) or non-critical residue (Q532A) of the BL signal sequence was mutated. We found that c-Kit-BL-A531G re-established apical distribution, whereas c-Kit-BL-Q532A remained at the basolateral surface. These results show that c-Kit behaved like an apical protein in the milieu of polarized epithelial cells and followed similar protein trafficking rules. We then asked if the apical trafficking capacity of c-Kit correlates with its ability to mediate SCF-induced proliferation of blood cells. We transduced c-Kit or c-Kit-BL into 32D cells, a mouse myelomonocytic cell line that normally does not express c-Kit and requires stimulation with hematopoietic growth factors to proliferate. Untransduced 32D cells proliferated only in response to IL3 stimulation, whereas c-Kit-transduced 32D cells also proliferated upon SCF simulation. By contrast, c-Kit-BL-transduced 32D cells behaved like the parental 32D cells and did not proliferate upon SCF stimulation, suggesting that a c-Kit mutant deficient in apical trafficking could not mediate proliferation. We next examined the effect of c-Kit or c-Kit-BL expression on polarization and proliferation of primary HSPC. We transduced mouse bone marrow cells to express either c-Kit or c-Kit-BL and examined for SCF-induced polarization. 76–96% of c-Kit-transduced HPSC exhibited polarization of markers Sca1, aPKC, β-catenin and annexin 2 upon SCF stimulation, whereas only 16–26% of c-Kit-BL-transduced cells underwent such polarization. We then cultured transduced bone marrow cells in methylcellulose in the presence of SCF to form colonies. c-Kit-transduced cells gave rise to discrete colonies but c-Kit-BL-transduced cells failed to produce any colonies, indicating that the c-Kit-BL mutant dominantly interfered with the ability of the endogenous c-Kit to promote proliferation. In summary, our data show that c-Kit trafficked selectively to an “apical” domain in epithelial cells and HSPC. A c-Kit mutant defective in the apical trafficking not only failed to induce blood cell proliferation but also suppressed the proliferative function of the endogenous c-Kit. Further delineation of the mechanism of apical trafficking of c-Kit should help elucidate the relationship between the cell polarity machinery and the regulation of HSPC proliferation. Disclosures: No relevant conflicts of interest to declare.