Synergistic roles of CBX4 chromo and SIM domains in regulating senescence of primary human osteoarthritic chondrocytes

BACKGROUND

Cellular senescence is a critical factor contributing to osteoarthritis (OA). Overexpression of chromobox homolog 4 (CBX4) in a mouse system was demonstrated to alleviate post-traumatic osteoarthritis (PTOA) by reducing cellular senescence. Additionally, replicative cellular senescence of WI-38 fibroblasts can be attenuated by CBX4. However, the mechanisms underlying this senomorphic function of CBX4 are not fully understood. In this study, we aimed to investigate the role of CBX4 in cellular senescence in human primary osteoarthritic chondrocytes and to identify the functional domains of CBX4 necessary for its function in modulating senescence.

METHODS

Chondrocytes, isolated from 6 individuals undergoing total knee replacement for OA, were transduced with wild-type CBX4, mutant CBX4, and control lentiviral constructs. Senescence-related phenotypic outcomes included the following: multiple flow cytometry-measured markers (p16INK4A, senescence-associated β-galactosidase [SA-β-gal] activity and dipeptidyl peptidase-4 [DPP4], and proliferation marker EdU), multiplex ELISA-measured markers in chondrocyte culture media (senescence-associated secretory phenotypes [SASPs], including IL-1β, IL-6, IL-8, TNF-α, MMP-1, MMP-3, and MMP-9), and PCR array-evaluated senescence-related genes.

RESULTS

Compared with control, CBX4 overexpression in OA chondrocytes decreased DPP4 expression and SASP secretion and increased chondrocyte proliferation confirming CBX4 senomorphic effects on primary human chondrocytes. Point mutations of the chromodomain domain (CDM, involved in chromatin modification) alone were sufficient to partially block the senomorphic activity of CBX4 (p16INK4A and DPP4 increased, and EdU decreased) but had minimal effect on SASP secretion. Although having no effect on p16INK4A, DPP4, and EdU, deletion of two small-ubiquitin-like-modifier-interaction motifs (CBX4 ΔSIMs) led to increased SASP secretion (IL-1β, TNF-α, IL-8). The combination CBX4 CDMΔSIMs altered all these measures adversely and to a greater degree than the single domain mutants. Deletion of the C-terminal (CBX4 ΔC-box) involved with transcriptional silencing of polycomb group proteins increased IL-1β slightly but significantly but altered none of the other senescence outcome measures.

CONCLUSIONS

CBX4 has a senomorphic effect on human osteoarthritic chondrocytes. CDM is critical for CBX4-mediated regulation of senescence. The SIMs are supportive but not indispensable for CBX4 senomorphic function while the C-box is dispensable.

Association of Dipeptidylpeptidase 4 (CD26) With Chondrocyte Senescence and Radiographic Progression in Knee Osteoarthritis

OBJECTIVE

To evaluate the association of dipeptidylpeptidase 4 (DPP-4; also known as CD26) with cellular senescence of human cartilage and progression of knee osteoarthritis (OA).

METHODS

Articular cartilage sections and chondrocytes were acquired from 35 individuals undergoing total knee replacement for OA to evaluate the following: 1) the association between OA severity and established senescence markers (senescence-associated β-galactosidase activity and p16), which was quantified using immunohistochemistry and flow cytometry (n = 19 samples); 2) the coexpression of DPP-4 with established senescence markers, which was assessed using flow cytometry; and 3) expression levels of anabolic and catabolic genes, senescence-related genes, and senescence-associated secretory phenotypes in DPP-4+ and DPP-4- cells, which were isolated using fluorescence-activated cell sorting or magnetic-activated cell sorting (n = 16 samples). The concentration of soluble DPP-4 was measured in samples of synovial fluid and samples of plasma from the Prediction of Osteoarthritis Progression cohort and then evaluated for association with the severity of radiographic knee OA at baseline (n = 65 samples) and the progression of structural radiographic OA (n = 57 samples) over a 3-year period.

RESULTS

DPP-4 expression was associated with higher senescence-associated β-galactosidase activity, p16 expression, senescence-related gene and catabolic gene (ADAMTS5, MMP13, IL6, and IL8) expression, higher senescence-associated secretory phenotype secretion, and lower anabolic gene (COL2A1 and ACAN) expression in primary chondrocytes. Synovial fluid DPP-4 concentration was associated with radiographic OA progression (odds ratio 105.32; P = 0.015), proteases (synovial fluid matrix metalloproteinase 1 and matrix metalloproteinase 3), aggrecan degradation (synovial fluid sulfated glycosaminoglycan), indicators of activated macrophages (synovial fluid CD14 and CD163), and inflammation (synovial fluid interleukin-6).

CONCLUSION

Our study identifies DPP-4 as a key surface marker in senescent chondrocytes and a predictor of radiographic OA progression.

A Validated Pre-operative Risk Prediction Tool for Extended Inpatient Length of Stay Following Primary Total Hip or Knee Arthroplasty

BACKGROUND

As value-based reimbursement models mature, understanding the potential trade-off between inpatient lengths of stay and complications or need for costly postacute care becomes more pressing. Understanding and predicting a patient's expected baseline length of stay may help providers understand how best to decide optimal discharge timing for high-risk total joint arthroplasty (TJA) patients.

METHODS

A retrospective review was conducted of 37,406 primary total hip (17,134, 46%) and knee (20,272, 54%) arthroplasties performed at two high-volume, geographically diverse, tertiary health systems during the study period. Patients were stratified by 3 binary outcomes for extended inpatient length of stay: 72 + hours (29%), 4 + days (11%), or 5 + days (5%). The predictive ability of over 50 sociodemographic/comorbidity variables was tested. Multivariable logistic regression models were created using institution #1 (derivation), with accuracy tested using the cohort from institution #2 (validation).

RESULTS

During the study period, patients underwent an extended length of stay with a decreasing frequency over time, with privately insured patients having a significantly shorter length of stay relative to those with Medicare (1.9 versus 2.3 days, P < .0001). Extended stay patients also had significantly higher 90-day readmission rates (P < .0001), even when excluding those discharged to postacute care (P < .01). Multivariable logistic regression models created from the training cohort demonstrated excellent accuracy (area under the curve (AUC): 0.755, 0.783, 0.810) and performed well under external validation (AUC: 0.719, 0.743, 0.763). Many important variables were common to all 3 models, including age, sex, American Society of Anesthesiologists (ASA) score, body mass index, marital status, bilateral case, insurance type, and 13 comorbidities.

DISCUSSION

An online, freely available, preoperative clinical decision tool accurately predicts risk of extended inpatient length of stay after TJA. Many risk factors are potentially modifiable, and these validated tools may help guide clinicians in preoperative patient counseling, medical optimization, and understanding optimal discharge timing.

A Weighted Index of Elixhauser Comorbidities for Predicting 90-day Readmission After Total Joint Arthroplasty

BACKGROUND

Evolving reimbursement models increasingly compel hospitals to assume costs for 90-day readmission after total joint arthroplasty. Although risk assessment tools exist, none currently reach the predictive performance required to accurately identify high-risk patients and modulate perioperative care accordingly. Although unlikely to perform adequately alone, the Elixhauser index is a set of 31 variables that may lend value in a broader model predicting 90-day readmission.

METHODS

Elixhauser comorbidities were examined in 10,022 primary unilateral total joint replacements, of which 4535 were hip replacements and 5487 were knee replacements, all performed between June 2013 and January 2018 at a single tertiary referral center. Data were extracted from electronic medical records using structured query language. After randomizing to derivation (80%) and validation (20%) subgroups, predictive models for 90-day readmission were generated and transformed into a system of weights based on each parameter's relative performance.

RESULTS

We observed 497 90-day readmissions (5.0%) during the study period, which demonstrated independent associations with 14 of the 31 Elixhauser comorbidity groups. A score created from the sum of each patient's weighted comorbidities did not lose substantial predictive discrimination (area under the curve: 0.653) compared to a comprehensive multivariable model containing all 31 unweighted Elixhauser parameters (area under the curve: 0.665). Readmission risk ranged from 3% for patients with a score of 0 to 27% for those with a score of 8 or higher.

CONCLUSIONS

The Elixhauser comorbidity score already meets or exceeds the predictive discrimination of available risk calculators. Although insufficient by itself, this score represents a valuable summary of patient comorbidities and merits inclusion in any broader model predicting 90-day readmission risk after total joint arthroplasty.

LEVEL OF EVIDENCE

III.

Diagnosis and management of laryngeal trauma in sports

The management of sports-related laryngeal trauma presents a diagnostic and therapeutic challenge. The application of basic treatment principles such as airway monitoring, thorough physical examination, and fiberoptic laryngeal examination will direct the management. Further radiologic examination or surgical intervention may be required to adequately assess and manage the injury. We review the diagnosis, treatment, and management in a case of laryngeal fracture that occurred during a National Hockey League game.

Depressed high-energy phosphate content in hypertrophied ventricles of animal and man: the biologic basis for increased sensitivity to ischemic injury

It is frequently stated that hypertrophied ventricles tolerate ischemia less well than nonhypertrophied ventricles. The authors' earlier studies in a rat supravalvular aortic stenosis model and canine valvular aortic stenosis model, both with concentric left ventricular hypertrophy, disclosed accelerated rates of ischemic contracture and diminished basal myocardial high energy phosphate stores. These studies have been extended to ten patients with severe left ventricular hypertrophy caused by valvular aortic stenosis and normal coronary arteries. ATP (endocardial and epicardial) from transmural left ventricular biopsies taken at operation before aorta cross-clamping, and frozen immediately in liquid nitrogen, were compared with similar biopsies from patients with nonhypertrophied myocardium supplied by normal coronary arteries. The subendocardial high energy phosphate levels in the nonhypertrophied myocardium was greater than high energy phosphate levels in the subepicardium of nonhypertrophied ventricles (ATP-micromoles/gram-protein, epi = 36.8 +/- 3.3, endo = 37.7 +/- 3.3) (p = NS). However, in the hypertrophied myocardium the subendocardium consistently showed significantly depressed high-energy phosphate levels when compared with subepicardial levels (ATP-hypertrophied myocardium, epi = 31.5 +/- 1.6, endo = 25.9 +/- 1.7) (p less than 0.05). This uniform depression of ATP stores, greatest in the subendocardium, in left ventricular hypertrophy suggests a common biologic mechanism for the enhanced sensitivity to ischemia. Of importance for patients may be the prior observation in rats that repletion of ATP( stores before ischemia eliminates the accelerated rate to ischemic contracture. Diminished subendocardial ATP stores appear to be an intrinsic property of severely hypertrophied myocardium and probably contribute to its enhanced sensitivity to ischemia.