Adipose tissue is a critical regulator of osteoarthritis.

Osteoarthritis (OA), the leading cause of pain and disability worldwide, disproportionally affects individuals with obesity. The mechanisms by which obesity leads to the onset and progression of OA are unclear due to the complex interactions among the metabolic, biomechanical, and inflammatory factors that accompany increased adiposity. We used a murine preclinical model of lipodystrophy (LD) to examine the direct contribution of adipose tissue to OA. Knee joints of LD mice were protected from spontaneous or posttraumatic OA, on either a chow or high-fat diet, despite similar body weight and the presence of systemic inflammation. These findings indicate that adipose tissue itself plays a critical role in the pathophysiology of OA. Susceptibility to posttraumatic OA was reintroduced into LD mice using implantation of a small adipose tissue depot derived from wild-type animals or mouse embryonic fibroblasts that undergo spontaneous adipogenesis, implicating paracrine signaling from fat, rather than body weight, as a mediator of joint degeneration.

Congenital lipodystrophy induces severe osteosclerosis.

Berardinelli-Seip congenital generalized lipodystrophy is associated with increased bone mass suggesting that fat tissue regulates the skeleton. Because there is little mechanistic information regarding this issue, we generated "fat-free" (FF) mice completely lacking visible visceral, subcutaneous and brown fat. Due to robust osteoblastic activity, trabecular and cortical bone volume is markedly enhanced in these animals. FF mice, like Berardinelli-Seip patients, are diabetic but normalization of glucose tolerance and significant reduction in circulating insulin fails to alter their skeletal phenotype. Importantly, the skeletal phenotype of FF mice is completely rescued by transplantation of adipocyte precursors or white or brown fat depots, indicating that adipocyte derived products regulate bone mass. Confirming such is the case, transplantation of fat derived from adiponectin and leptin double knockout mice, unlike that obtained from their WT counterparts, fails to normalize FF bone. These observations suggest a paucity of leptin and adiponectin may contribute to the increased bone mass of Berardinelli-Seip patients.

Can Outpatient Plastic Surgery Be Done Safely During a COVID-19 Surge? Results of a July 2020 Los Angeles Survey and Literature Review.

BACKGROUND: A moratorium was placed on nonurgent surgery throughout much of the United States in mid-March 2020 due to surging numbers of COVID-19 cases. Several months later, and with new safety precautions in place, elective surgery gradually resumed. However, no data exist on the safety of plastic surgery during the pandemic. OBJECTIVES: This aim of this survey was to assess the safety of plastic surgery during the pandemic by quantifying: (1) the preoperative prevalence of SARS-CoV-2; (2) the risk of postoperative COVID-19; (3) outcomes and precious resource utilization for such cases; and (4) the risks to office staff. METHODS: Los Angeles plastic surgeons certified by the American Board of Plastic Surgery (ABPS) were sent an online survey in July 2020, during a local COVID-19 surge, querying about the number of procedures performed in the 8- to 10-week period since reopening, testing policies, surgical complications, and cases among staff. RESULTS: In total, 112 surgeons reported 5633 surgeries since resuming elective surgery. Of these, 103 (91.96%) surgeons obtained a preoperative SARS-CoV-2 polymerase chain reaction (PCR) test for every patient. The preoperative PCR test was positive in 41/5881 (0.69%). Positive tests within 2 weeks postoperation occurred in 7/5380 (0.13%) of surgical patients, 3/8506 (0.04%) of injection patients, and 6/2519 (0.24%) of energy therapy patients. Nine offices reported at least 1 staff member who developed COVID-19. All cases were mild, with no hospitalizations or deaths. CONCLUSIONS: These data demonstrate that plastic surgery can be performed safely during a COVID-19 surge by ABPS diplomates. This has profound impact for patients, plastic surgeons, and health policy regulators.

Why Do We Need Anatomical Implants? the Science and Rationale for Maintaining Their Availability and Use in Breast Surgery.

The choice between anatomical and round implants is an important decision in breast augmentation surgery; however, both have their place and the decision between them that should be made on a patient-by-patient basis, taking into account the patient's desires, anatomy, and surgical history. In some individuals, there are clear indications for using either anatomical or round devices, and there is good evidence that aesthetic outcomes are better with anatomical implants in some instances. When both types are an option, anatomical devices may offer increased flexibility and, despite a longer learning curve needed to properly manage them, they are associated with positive long-term outcomes and high levels of patient satisfaction. Concerns about implant rotation can be minimized with proper patient selection and surgical technique, and the overall complication rate may favor anatomical over round devices in appropriate patients. Breast implant-associated anaplastic large-cell lymphoma is an important issue, and while rare, it must be considered in the context of the entire patient risk profile. Both anatomical and round implants remain key elements of a complete surgical toolbox in breast augmentation. LEVEL OF EVIDENCE IV: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

Report on Mortality from Gluteal Fat Grafting: Recommendations from the ASERF Task Force.

Background: Gluteal fat grafting is among the fastest growing aesthetic procedures in the United States and around the world. Given numerous anecdotal and published reports of fatal and nonfatal pulmonary fat embolism resulting from this procedure, the Aesthetic Surgery Education and Research Foundation (ASERF) formed a Task Force to study this complication. Objectives: To determine the incidence of fatal and nonfatal pulmonary fat embolism associated with gluteal fat grafting and provide recommendations to decrease the risks of the procedure. Methods: An anonymous web-based survey was sent to 4843 plastic surgeons worldwide. Additional data on morbidity and mortality was collected through confidential interviews with plastic surgeons and medical examiners, public records requests for autopsy reports in the United States, and through the American Association for the Accreditation of Ambulatory Surgical Facilities (AAAASF). Results: Six hundred and ninety-two (692) surgeons responding to the survey reported 198,857 cases of gluteal fat grafting. Over their careers, surgeons reported 32 fatalities from pulmonary fat emboli as well as 103 nonfatal pulmonary fat emboli. Three percent (3%) of respondents experienced a patient fatality and 7% of respondents reported at least one pulmonary fat embolism in a patient over their careers. Surgeons reporting the practice of injecting into the deep muscle experienced a significantly increased incidence rate of fatal and nonfatal pulmonary fat emboli. Twenty-five fatalities were confirmed in the United States over the last 5 years through of autopsy reports and interviews with surgeons and medical examiners. Four deaths were reported from 2014 to 2015 from pulmonary fat emboli in AAAASF facilities. Conclusions: Despite the growing popularity of gluteal fat grafting, significantly higher mortality rates appear to be associated with gluteal fat grafting than with any other aesthetic surgical procedure. Based on this survey, fat injections into the deep muscle, using cannulae smaller than 4 mm, and pointing the injection cannula downwards should be avoided. More research is necessary to increase the safety of this procedure.

Therapeutic implications of suppressing osteoclast formation versus function.

Anti-resorptive therapy is the principal means of treating osteoporotic disorders. The two families of presently available anti-resorptive drugs, namely bisphosphonates and denosumab, dampen activity of osteoclasts by reducing their number. In consequence, these agents also arrest bone remodelling eventuating suppressed formation as well as resorption. Evidence exists that osteoclasts recruit osteoblasts to sites of bone remodelling by mobilizing chemotactic proteins from matrix and direct secretion of such proteins that attract osteoblast precursors. Thus, anti-resorptive agents, such as the cathepsin K inhibitor odanacatib, that dampen osteoclast function but not number may also preserve osteoblast recruitment by preserving the bone resorptive cell.

DAP12 couples c-Fms activation to the osteoclast cytoskeleton by recruitment of Syk.

We examined the mechanism by which M-CSF regulates the cytoskeleton and function of the osteoclast, the exclusive bone resorptive cell. We show that binding of M-CSF to its receptor c-Fms generates a signaling complex comprising phosphorylated DAP12, an adaptor containing an immunoreceptor tyrosine-based activation motif (ITAM) and the nonreceptor tyrosine kinase Syk. c-Fms tyrosine 559, the exclusive binding site of c-Src, is necessary for regulation of DAP12/Syk signaling. Deletion of either of these molecules yields osteoclasts that fail to reorganize their cytoskeleton. Retroviral transduction of null precursors with wild-type or mutant DAP12 or Syk reveals that the SH2 domain of Syk and the ITAM tyrosine residues and transmembrane domain of DAP12 mediate M-CSF signaling. Our data provide genetic and biochemical evidence that uncovers an epistatic signaling pathway linking the receptor tyrosine kinase c-Fms to the immune adaptor DAP12 and the cytoskeleton.

Vinculin regulates osteoclast function.

Osteoclastic bone resorption depends upon the cell's ability to organize its cytoskeleton. Because vinculin (VCL) is an actin-binding protein, we asked whether it participates in skeletal degradation. Thus, we mated VCL(fl/fl) mice with those expressing cathepsin K-Cre (CtsK-VCL) to delete the gene in mature osteoclasts or lysozyme M-Cre (LysM-VCL) to target all osteoclast lineage cells. VCL-deficient osteoclasts differentiate normally but, reflecting cytoskeletal disorganization, form small actin rings and fail to effectively resorb bone. In keeping with inhibited resorptive function, CtsK-VCL and LysM-VCL mice exhibit a doubling of bone mass. Despite cytoskeletal disorganization, the capacity of VCL(-/-) osteoclastic cells to normally phosphorylate c-Src in response to αvß3 integrin ligand is intact. Thus, integrin-activated signals are unrelated to the means by which VCL organizes the osteoclast cytoskeleton. WT VCL completely rescues actin ring formation and bone resorption, as does VCL(P878A), which is incapable of interacting with Arp2/3. As expected, deletion of the VCL tail domain (VCL(1-880)), which binds actin, does not normalize VCL(-/-) osteoclasts. The same is true regarding VCL(I997A), which also prevents VCL/actin binding, and VCL(A50I) and VCL(811-1066), both of which arrest talin association. Thus, VCL binding talin, but not Arp2/3, is critical for osteoclast function, and its selective inhibition retards physiological bone loss.

Correlating RANK ligand/RANK binding kinetics with osteoclast formation and function.

The interaction between Receptor Activator of NF-κB Ligand (RANKL) and its receptor RANK is essential for the differentiation and bone resorbing capacity of the osteoclast. Osteoprotegerin (OPG), a soluble homodimer, acts as a decoy receptor for RANKL and thus inhibits osteoclastogenesis. An imbalance in the RANKL/RANK/OPG axis, with decreased OPG and/or increased RANKL, is associated with diseases that favor bone loss, including osteoporosis. Recently, we established a yeast surface display system and screened libraries of randomly mutated RANKL proteins to identify mutations that abolish binding to OPG while preserving recognition of RANK. These efforts yielded several RANKL variants possessing substantially higher affinity for RANK compared to their wild-type (WT) counterpart. Using recombinant RANKL mutant proteins, we find those with increased affinity for RANK produce more robust signaling in osteoclast lineage cells and have greater osteoclastogenic potential. Our results are the first to document gain of function RANKL mutations. They indicate that the physiological RANKL/RANK interaction is not optimized for maximal signaling and function, perhaps reflecting the need to maintain receptor specificity within the tumor necrosis factor superfamily (TNFSF). Instead, we find, a biphasic relationship exists between RANKL/RANK affinity and osteoclastogenic capacity. In our panel of RANKL variants, this relationship is driven entirely by manipulation of the kinetic off-rate. Our structure-based and yeast surface display-derived insights into manipulating this critical signaling axis may aid in the design of novel anti-resorptive therapies as well as provide a paradigm for design of other receptor-specific TNF superfamily ligand variants.

Glucocorticoids and the osteoclast.

Glucocorticoid-induced osteoporosis uniformly represents suppression of bone formation. The steroid's effects on osteoclasts are, however, controversial. While glucocorticoid administration to patients with inflammatory diseases accelerates bone resorption, osteoclast function falls below normal with prolonged treatment. Thus, administration of anti-resorptive agents, such as bisphosphonates, is justified during early glucocorticoid therapy, but further suppression of osteoclasts, by these drugs, in chronically treated patients will dampen bone remodelling and may compromise skeletal quality, predisposing to fracture.

Histological characterization of human breast implant capsules.

BACKGROUND: This study investigated the relationships between histomorphological aspects of breast capsules, including capsule thickness, collagen fiber alignment, the presence of α-smooth muscle actin (α-SMA)-positive myofibroblasts, and clinical observations of capsular contracture. METHODS: Breast capsule samples were collected at the time of implant removal in patients undergoing breast implant replacement or revision surgery. Capsular contracture was scored preoperatively using the Baker scale. Histological analysis included hematoxylin and eosin staining, quantitative analysis of capsule thickness, collagen fiber alignment, and immunohistochemical evaluation for α-SMA and CD68. RESULTS: Forty-nine samples were harvested from 41 patients. A large variation in histomorphology was observed between samples, including differences in cellularity, fiber density and organization, and overall structure. Baker I capsules were significantly thinner than Baker II, III, and IV capsules. Capsule thickness positively correlated with implantation time for all capsules and for contracted capsules (Baker III and IV). Contracted capsules had significantly greater collagen fiber alignment and α-SMA-positive immunoreactivity than uncontracted capsules (Baker I and II). Capsules from textured implants had significantly less α-SMA-positive immunoreactivity than capsules from smooth implants. CONCLUSION: The histomorphological diversity observed between the breast capsules highlights the challenges of identifying mechanistic trends in capsular contracture. Our findings support the role of increasing capsule thickness and collagen fiber alignment, and the presence of contractile myofibroblasts in the development of contracture. These changes in capsule structure may be directly related to palpation stiffness considered in the Baker score. Approaches to disrupt these processes may aid in decreasing capsular contracture rates. LEVEL OF EVIDENCE III: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Type I phosphotidylinosotol 4-phosphate 5-kinase γ regulates osteoclasts in a bifunctional manner.

Type 1 phosphotidylinosotol-4 phosphate 5 kinase γ (PIP5KIγ) is central to generation of phosphotidylinosotol (4,5)P(2) (PI(4,5)P(2)). PIP5KIγ also participates in cytoskeletal organization by delivering talin to integrins, thereby enhancing their ligand binding capacity. As the cytoskeleton is pivotal to osteoclast function, we hypothesized that absence of PIP5KIγ would compromise their resorptive capacity. Absence of the kinase diminishes PI(4,5) abundance and desensitizes precursors to RANK ligand-stimulated differentiation. Thus, PIP5KIγ(-/-) osteoclasts are reduced in number in vitro and confirm physiological relevance in vivo. Despite reduced numbers, PIP5KIγ(-/-) osteoclasts surprisingly have normal cytoskeletons and effectively resorb bone. PIP5KIγ overexpression, which increases PI(4,5)P(2), also delays osteoclast differentiation and reduces cell number but in contrast to cells lacking the kinase, its excess disrupts the cytoskeleton. The cytoskeleton-disruptive effects of excess PIP5KIγ reflect its kinase activity and are independent of talin recognition. The combined arrested differentiation and disorganized cytoskeleton of PIP5KIγ-transduced osteoclasts compromises bone resorption. Thus, optimal PIP5KIγ and PI(4,5)P(2) expression, by osteoclasts, are essential for skeletal homeostasis.

Mouse genome-wide association and systems genetics identify Asxl2 as a regulator of bone mineral density and osteoclastogenesis.

Significant advances have been made in the discovery of genes affecting bone mineral density (BMD); however, our understanding of its genetic basis remains incomplete. In the current study, genome-wide association (GWA) and co-expression network analysis were used in the recently described Hybrid Mouse Diversity Panel (HMDP) to identify and functionally characterize novel BMD genes. In the HMDP, a GWA of total body, spinal, and femoral BMD revealed four significant associations (-log10P>5.39) affecting at least one BMD trait on chromosomes (Chrs.) 7, 11, 12, and 17. The associations implicated a total of 163 genes with each association harboring between 14 and 112 genes. This list was reduced to 26 functional candidates by identifying those genes that were regulated by local eQTL in bone or harbored potentially functional non-synonymous (NS) SNPs. This analysis revealed that the most significant BMD SNP on Chr. 12 was a NS SNP in the additional sex combs like-2 (Asxl2) gene that was predicted to be functional. The involvement of Asxl2 in the regulation of bone mass was confirmed by the observation that Asxl2 knockout mice had reduced BMD. To begin to unravel the mechanism through which Asxl2 influenced BMD, a gene co-expression network was created using cortical bone gene expression microarray data from the HMDP strains. Asxl2 was identified as a member of a co-expression module enriched for genes involved in the differentiation of myeloid cells. In bone, osteoclasts are bone-resorbing cells of myeloid origin, suggesting that Asxl2 may play a role in osteoclast differentiation. In agreement, the knockdown of Asxl2 in bone marrow macrophages impaired their ability to form osteoclasts. This study identifies a new regulator of BMD and osteoclastogenesis and highlights the power of GWA and systems genetics in the mouse for dissecting complex genetic traits.

Pulmonary osteoclast-like cells in silica induced pulmonary fibrosis.

The pathophysiology of silicosis is poorly understood, limiting development of therapies for those who have been exposed to the respirable particle. We explored mechanisms of silica-induced pulmonary fibrosis in human lung samples collected from patients with occupational exposure to silica and in a longitudinal mouse model of silicosis using multiple modalities including whole-lung single-cell RNA sequencing and histological, biochemical, and physiologic assessments. In addition to pulmonary inflammation and fibrosis, intratracheal silica challenge induced osteoclast-like differentiation of alveolar macrophages and recruited monocytes, driven by induction of the osteoclastogenic cytokine, receptor activator of nuclear factor κΒ ligand (RANKL) in pulmonary lymphocytes, and alveolar type II cells. Anti-RANKL monoclonal antibody treatment suppressed silica-induced osteoclast-like differentiation in the lung and attenuated pulmonary fibrosis. We conclude that silica induces differentiation of pulmonary osteoclast-like cells leading to progressive lung injury, likely due to sustained elaboration of bone-resorbing proteases and hydrochloric acid. Interrupting osteoclast-like differentiation may therefore constitute a promising avenue for moderating lung damage in silicosis.

Zap70 inhibits Syk-mediated osteoclast function.

The αvß3 integrin stimulates the resorptive capacity of the differentiated osteoclast (OC) by organizing its cytoskeleton via the tyrosine kinase, Syk. Thus, Syk-deficient OCs fails to spread or form actin rings, in vitro and in vivo. The Syk family of tyrosine kinases consists of Syk itself and Zap70 which are expressed by different cell types. Because of their structural similarity, and its compensatory properties in other cells, we asked if Zap70 can substitute for absence of Syk in OCs. While expression of Syk, as expected, normalizes the cytoskeletal abnormalities of Syk(-/-) OCs, Zap70 fails do so. In keeping with this observation, Syk, but not Zap70, rescues αvß3 integrin-induced SLP76 phosphorylation in Syk(-/-) OCs. Furthermore the kinase sequence of Syk partially rescues the Syk(-/-) phenotype but full normalization also requires its SH2 domains. Surprisingly, expression of Zap70 inhibits WT OC spreading, actin ring formation and bone resorptive activity, but not differentiation. In keeping with arrested cytoskeletal organization, Zap70 blocks integrin-activated endogenous Syk and Vav3, SLP76 phosphorylation. Such inhibition requires Zap70 kinase activity, as it is abolished by mutation of the Zap70 kinase domain. Thus, while the kinase domain of Syk is uniquely required for OC function that of Zap70 inhibits it.

Rac deletion in osteoclasts causes severe osteopetrosis.

Cdc42 mediates bone resorption principally by stimulating osteoclastogenesis. Whether its sister GTPase, Rac, meaningfully impacts upon the osteoclast and, if so, by what means, is unclear. We find that whereas deletion of Rac1 or Rac2 alone has no effect, variable reduction of Rac1 in osteoclastic cells of Rac2(-/-) mice causes severe osteopetrosis. Osteoclasts lacking Rac1 and Rac2 in combination (Rac double-knockout, RacDKO), fail to effectively resorb bone. By contrast, osteoclasts are abundant in RacDKO osteopetrotic mice and, unlike those deficient in Cdc42, express the maturation markers of the cells normally. Hence, the osteopetrotic lesion of RacDKO mice largely reflects impaired function, and not arrested differentiation, of the resorptive polykaryon. The dysfunction of RacDKO osteoclasts represents failed cytoskeleton organization as evidenced by reduced motility of the cells and their inability to spread or generate the key resorptive organelles (i.e. actin rings and ruffled borders), which is accompanied by abnormal Arp3 distribution. The cytoskeleton-organizing capacity of Rac1 is mediated through its 20-amino-acid effector domain. Thus, Rac1 and Rac2 are mutually compensatory. Unlike Cdc42 deficiency, their combined absence does not impact upon differentiation but promotes severe osteopetrosis by dysregulating the osteoclast cytoskeleton.