Mathematical modelling reveals unexpected inheritance and variability patterns of cell cycle parameters in mammalian cells.

The cell cycle is the fundamental process of cell populations, it is regulated by environmental cues and by intracellular checkpoints. Cell cycle variability in clonal cell population is caused by stochastic processes such as random partitioning of cellular components to progeny cells at division and random interactions among biomolecules in cells. One of the important biological questions is how the dynamics at the cell cycle scale, which is related to family dependencies between the cell and its descendants, affects cell population behavior in the long-run. We address this question using a "mechanistic" model, built based on observations of single cells over several cell generations, and then extrapolated in time. We used cell pedigree observations of NIH 3T3 cells including FUCCI markers, to determine patterns of inheritance of cell-cycle phase durations and single-cell protein dynamics. Based on that information we developed a hybrid mathematical model, involving bifurcating autoregression to describe stochasticity of partitioning and inheritance of cell-cycle-phase times, and an ordinary differential equation system to capture single-cell protein dynamics. Long-term simulations, concordant with in vitro experiments, demonstrated the model reproduced the main features of our data and had homeostatic properties. Moreover, heterogeneity of cell cycle may have important consequences during population development. We discovered an effect similar to genetic drift, amplified by family relationships among cells. In consequence, the progeny of a single cell with a short cell cycle time had a high probability of eventually dominating the population, due to the heritability of cell-cycle phases. Patterns of epigenetic heritability in proliferating cells are important for understanding long-term trends of cell populations which are either required to provide the influx of maturing cells (such as hematopoietic stem cells) or which started proliferating uncontrollably (such as cancer cells).

Mutation, drift and selection in single-driver hematologic malignancy: Example of secondary myelodysplastic syndrome following treatment of inherited neutropenia.

Cancer development is driven by series of events involving mutations, which may become fixed in a tumor via genetic drift and selection. This process usually includes a limited number of driver (advantageous) mutations and a greater number of passenger (neutral or mildly deleterious) mutations. We focus on a real-world leukemia model evolving on the background of a germline mutation. Severe congenital neutropenia (SCN) evolves to secondary myelodysplastic syndrome (sMDS) and/or secondary acute myeloid leukemia (sAML) in 30-40%. The majority of SCN cases are due to a germline ELANE mutation. Acquired mutations in CSF3R occur in >70% sMDS/sAML associated with SCN. Hypotheses underlying our model are: an ELANE mutation causes SCN; CSF3R mutations occur spontaneously at a low rate; in fetal life, hematopoietic stem and progenitor cells expands quickly, resulting in a high probability of several tens to several hundreds of cells with CSF3R truncation mutations; therapeutic granulocyte colony-stimulating factor (G-CSF) administration early in life exerts a strong selective pressure, providing mutants with a growth advantage. Applying population genetics theory, we propose a novel two-phase model of disease development from SCN to sMDS. In Phase 1, hematopoietic tissues expand and produce tens to hundreds of stem cells with the CSF3R truncation mutation. Phase 2 occurs postnatally through adult stages with bone marrow production of granulocyte precursors and positive selection of mutants due to chronic G-CSF therapy to reverse the severe neutropenia. We predict the existence of the pool of cells with the mutated truncated receptor before G-CSF treatment begins. The model does not require increase in mutation rate under G-CSF treatment and agrees with age distribution of sMDS onset and clinical sequencing data.

Influence of gender on age of treatment with TKA and functional outcome.

BACKGROUND: Previous studies suggest differences may exist between men and women in terms of knee function before and after total knee replacement. This may be related to the efficacy of the procedure itself or to differences in the severity of disability of male and female patients at the time of surgery. QUESTIONS/PURPOSES: We evaluated differences in the age, preoperative deformity, range-of-motion, and Knee Society scores of men and women who underwent TKA. All parameters were measured at the time of the initial preoperative evaluation and at postoperative followup. METHODS: We studied 698 patients who underwent elective TKA between 1996 and 2007. This population consisted of 428 women (61%) and 270 men (39%), all of whom underwent rehabilitation utilizing a standardized hyperflexion protocol with immediate initiation of full weight-bearing postoperatively. RESULTS: The men were on average three years younger than the women (mean 63.5 versus 66.6 years, respectively). Preoperative ROM, postoperative ROM, and changes in ROM and body mass index were similar between groups. Knee Society Knee scores were similar preoperatively (47.4 [men] versus 46.7 [women]), but four points higher in men at followup (89.2 versus 85.2). Women had lower Knee Function scores than men preoperatively (45.2 versus 57.1), and postoperatively (65.3 versus 73.9). CONCLUSIONS: Women who undergo TKA seek treatment at a later stage than men and have greater functional disability at the time of surgery. Differences in functional scores persist after TKA. Earlier initiation of treatment may enhance postoperative outcome. LEVEL OF EVIDENCE: Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Implant durability and knee function after total knee arthroplasty in the morbidly obese patient.

This study investigated the effect of body mass index (BMI) on outcomes after cemented tricompartmental total knee arthroplasty (TKA). Functional and radiographic Knee Society scores in 71 patients (94 knees) with BMI 30 to 39 and 31 patients (41 knees) with BMI > or =40 were compared with 67 patients (85 knees) with BMI 20 to 29 at a mean follow-up of 5.4 years. Total knee arthroplasty rates of success (79%), complication (17%), and revision (6%) were independent of BMI. The BMI > or =40 group, however, was 5.4x (95% confidence interval, 2.1-14.7) more likely to develop patellar radiolucencies, had poorer hamstring and quadriceps conditioning, and had more patellofemoral symptoms. Forty percent of TKAs at BMI > or =40 with patellar radiolucencies failed. In conclusion, TKA benefits were realized at all BMI, but at BMI > or =40, more rehabilitation and monitoring are recommended.

Dynamic cross talk model of the epithelial innate immune response to double-stranded RNA stimulation: coordinated dynamics emerging from cell-level noise.

We present an integrated dynamical cross-talk model of the epithelial innate immune response (IIR) incorporating RIG-I and TLR3 as the two major pattern recognition receptors (PRR) converging on the RelA and IRF3 transcriptional effectors. bioPN simulations reproduce biologically relevant gene-and protein abundance measurements in response to time course, gene silencing and dose-response perturbations both at the population and single cell level. Our computational predictions suggest that RelA and IRF3 are under auto- and cross-regulation. We predict, and confirm experimentally, that RIG-I mRNA expression is controlled by IRF7. We also predict the existence of a TLR3-dependent, IRF3-independent transcription factor (or factors) that control(s) expression of MAVS, IRF3 and members of the IKK family. Our model confirms the observed dsRNA dose-dependence of oscillatory patterns in single cells, with periods of 1-3 hr. Model fitting to time series, matched by knockdown data suggests that the NF-κB module operates in a different regime (with different coefficient values) than in the TNFα-stimulation experiments. In future studies, this model will serve as a foundation for identification of virus-encoded IIR antagonists and examination of stochastic effects of viral replication. Our model generates simulated time series, which reproduce the noisy oscillatory patterns of activity (with 1-3 hour period) observed in individual cells. Our work supports the hypothesis that the IIR is a phenomenon that emerged by evolution despite highly variable responses at an individual cell level.

Posterior cruciate ligament substitution is not essential for excellent postoperative outcomes in total knee arthroplasty.

The study compared postoperative range of motion (ROM) and functional outcome of total knee arthroplasty (TKA) with a posterior cruciate ligament (PCL)-substituting knee prosthesis compared with an ultracongruent PCL-sacrificing design. Two hundred nine patients underwent primary TKA. Posterior stabilized design (121) and highly conforming, PCL-sacrificing, ultracongruent design (88) TKAs were reviewed. Surgeon, surgical approach, and a hyperflexion postoperative rehabilitation protocol were the same. Results showed significant improvement in knee flexion, ROM, Knee Score, and Function Score within each group. Postoperative mean total ROM was slightly higher with the posterior stabilized design. The 2 groups were the same postoperatively in the improvement in ROM, Knee Score, Function Score, satisfaction level, among other activity metrics. There was no clear evidence proving superiority and the need for posterior stabilization in PCL-sacrificing TKA.

The PCL significantly affects the functional outcome of total knee arthroplasty.

This study tests the hypothesis that patients receiving a posterior cruciate ligament (PCL)-retaining prosthesis have no difference in functional outcome compared to those receiving a cruciate-sacrificing, posterior-stabilized (PS) design. Forty-nine patients underwent a total knee arthroplasty (TKA), performed by a single surgeon using the same implant design with either a PCL-retaining or a PS tibial insert. Each patient completed a self-administered, validated Total Knee Function Questionnaire as well as the SF-36. At 1-year follow-up, each patient's range of motion and Knee Society knee score were measured. There were no statistically significant differences between the 2 groups using the traditional measures of function following total knee replacement, including overall satisfaction with surgery. However, the TKFQ revealed that patients with PS knees reported greater functional limitations in squatting, kneeling, and gardening. Our results suggest that with the specific implant used in this study, substitution for the PCL with a spine and cam mechanism may not fully restore the functional capacity of the intact PCL, particularly in high-demand activities that involve deep flexion.

Mechanical alignment of tibial stems in revision total knee arthroplasty.

This multicenter, retrospective study evaluates the radiographic results of achieving optimal tibial alignment in revision total knee arthroplasty (TKA) using a single modular CoCr cemented or cementless stemmed implant design. Stem size and length also were evaluated. The hundred ninety-nine revision TKAs were performed between January 1993 and January 1996 by 13 experienced revision knee surgeons. The cases were subdivided into 5 comparative groups: (1) cemented stems, (2) 140-mm length canal-filling stems, (3) 140-mm length non-canal-filling stems, (4) 95-mm length canal-filling stems, and (5) 95-mm length non-canal-filling stems. The anteroposterior (AP) tibial alignment angle was measured. The canal-filling ratio (CFR) was determined by dividing the stem diameter by the endosteal diameter at the stem tip. Overall, the ability to achieve tibial alignment in the AP plane was more predictable when canal-filling (CFR >/= 0.85) cementless stems were used. This was further enhanced when long canal-filling cementless stems were selected. The least-predictable results and the highest probability of varus malalignment were achieved with cemented stems.