Interaction of Materials and Biology in Total Joint Replacement - Successes, Challenges and Future Directions

Total joint replacement (TJR) has revolutionized the treatment of end-stage arthritic disorders. This success is due, in large part, to a clear understanding of the important interaction between the artificial implant and the biology of the host. All surgical procedures in which implants are placed in the body evoke an initial inflammatory reaction, which generally subsides over several weeks. Thereafter, a series of homeostatic events occur leading to progressive integration of the implant within bone and the surrounding musculoskeletal tissues. The eventual outcome of the operation is dependent on the characteristics of the implant, the precision of the surgical technique and operative environment, and the biological milieu of the host. If these factors and events are not optimal, adverse events can occur such as the development of chronic inflammation, progressive bone loss due to increased production of degradation products from the implant (periprosthetic osteolysis), implant loosening or infection. These complications can lead to chronic pain and poor function of the joint reconstruction, and may necessitate revision surgery or removal of the prosthesis entirely. Recent advances in engineering, materials science, and the immunological aspects associated with orthopaedic implants have fostered intense research with the hope that joint replacements will last a lifetime, and facilitate pain-free, normal function.

Ca²⁺ signals promote GLUT4 exocytosis and reduce its endocytosis in muscle cells

Elevating cytosolic Ca(2+) stimulates glucose uptake in skeletal muscle, but how Ca(2+) affects intracellular traffic of GLUT4 is unknown. In tissue, changes in Ca(2+) leading to contraction preclude analysis of the impact of individual, Ca(2+)-derived signals. In L6 muscle cells stably expressing GLUT4myc, the Ca(2+) ionophore ionomycin raised cytosolic Ca(2+) and caused a gain in cell surface GLUT4myc. Extra- and intracellular Ca(2+) chelators (EGTA, BAPTA-AM) reversed this response. Ionomycin activated calcium calmodulin kinase II (CaMKII), AMPK, and PKCs, but not Akt. Silencing CaMKIIδ or AMPKα1/α2 partly reduced the ionomycin-induced gain in surface GLUT4myc, as did peptidic or small molecule inhibitors of CaMKII (CN21) and AMPK (Compound C). Compared with the conventional isoenzyme PKC inhibitor Gö6976, the conventional plus novel PKC inhibitor Gö6983 lowered the ionomycin-induced gain in cell surface GLUT4myc. Ionomycin stimulated GLUT4myc exocytosis and inhibited its endocytosis in live cells. siRNA-mediated knockdown of CaMKIIδ or AMPKα1/α2 partly reversed ionomycin-induced GLUT4myc exocytosis but did not prevent its reduced endocytosis. Compared with Gö6976, Gö6983 markedly reversed the slowing of GLUT4myc endocytosis triggered by ionomycin. In summary, rapid Ca(2+) influx into muscle cells accelerates GLUT4myc exocytosis while slowing GLUT4myc endocytosis. CaMKIIδ and AMPK stimulate GLUT4myc exocytosis, whereas novel PKCs reduce endocytosis. These results identify how Ca(2+)-activated signals selectively regulate GLUT4 exocytosis and endocytosis in muscle cells.

The Drosophila circadian clock is a variably coupled network of multiple peptidergic units

Daily rhythms in behavior emerge from networks of neurons that express molecular clocks. Drosophila's clock neuron network consists of a diversity of cell types, yet is modeled as two hierarchically organized groups, one of which serves as a master pacemaker. Here, we establish that the fly's clock neuron network consists of multiple units of independent neuronal oscillators, each unified by its neuropeptide transmitter and mode of coupling to other units. Our work reveals that the circadian clock neuron network is not orchestrated by a small group of master pacemakers but rather consists of multiple independent oscillators, each of which drives rhythms in activity.

DJ-1 protects against cell death following acute cardiac ischemia-reperfusion injury

Novel therapeutic targets are required to protect the heart against cell death from acute ischemia-reperfusion injury (IRI). Mutations in the DJ-1 (PARK7) gene in dopaminergic neurons induce mitochondrial dysfunction and a genetic form of Parkinson's disease. Genetic ablation of DJ-1 renders the brain more susceptible to cell death following ischemia-reperfusion in a model of stroke. Although DJ-1 is present in the heart, its role there is currently unclear. We sought to investigate whether mitochondrial DJ-1 may protect the heart against cell death from acute IRI by preventing mitochondrial dysfunction. Overexpression of DJ-1 in HL-1 cardiac cells conferred the following beneficial effects: reduced cell death following simulated IRI (30.4±4.7% with DJ-1 versus 52.9±4.7% in control; n=5, P<0.05); delayed mitochondrial permeability transition pore (MPTP) opening (a critical mediator of cell death) (260±33 s with DJ-1 versus 121±12 s in control; n=6, P<0.05); and induction of mitochondrial elongation (81.3±2.5% with DJ-1 versus 62.0±2.8% in control; n=6 cells, P<0.05). These beneficial effects of DJ-1 were absent in cells expressing the non-functional DJ-1(L166P) and DJ-1(Cys106A) mutants. Adult mice devoid of DJ-1 (KO) were found to be more susceptible to cell death from in vivo IRI with larger myocardial infarct sizes (50.9±3.5% DJ-1 KO versus 41.1±2.5% in DJ-1 WT; n≥7, P<0.05) and resistant to cardioprotection by ischemic preconditioning. DJ-1 KO hearts showed increased mitochondrial fragmentation on electron microscopy, although there were no differences in calcium-induced MPTP opening, mitochondrial respiratory function or myocardial ATP levels. We demonstrate that loss of DJ-1 protects the heart from acute IRI cell death by preventing mitochondrial dysfunction. We propose that DJ-1 may represent a novel therapeutic target for cardioprotection.

Novel biological strategies for treatment of wear particle-induced periprosthetic osteolysis of orthopaedic implants for joint replacement

Wear particles and by-products from joint replacements and other orthopaedic implants may result in a local chronic inflammatory and foreign body reaction. This may lead to persistent synovitis resulting in joint pain and swelling, periprosthetic osteolysis, implant loosening and pathologic fracture. Strategies to modulate the adverse effects of wear debris may improve the function and longevity of joint replacements and other orthopaedic implants, potentially delaying or avoiding complex revision surgical procedures. Three novel biological strategies to mitigate the chronic inflammatory reaction to orthopaedic wear particles are reported. These include (i) interference with systemic macrophage trafficking to the local implant site, (ii) modulation of macrophages from an M1 (pro-inflammatory) to an M2 (anti-inflammatory, pro-tissue healing) phenotype in the periprosthetic tissues, and (iii) local inhibition of the transcription factor nuclear factor kappa B (NF-κB) by delivery of an NF-κB decoy oligodeoxynucleotide, thereby interfering with the production of pro-inflammatory mediators. These three approaches have been shown to be viable strategies for mitigating the undesirable effects of wear particles in preclinical studies. Targeted local delivery of specific biologics may potentially extend the lifetime of orthopaedic implants.

Abstract PD1-8: Acquired resistance to rapamycin and mTOR kinase inhibitors is mediated by non-overlapping mutations in distinct sites in the mTOR protein

The mammalian target of rapamycin (mTOR) protein kinase regulates protein translation and proliferation by integrating the availability of energy, nutrients and the presence of growth factors. Dysregulation of mTOR is a common event in human tumors and results from mutational activation of receptor tyrosine kinases, PI3K signaling or inactivating mutations of the Tuberous Sclerosis or GATOR complexes as well as the LKB/AMP kinase pathway.

The prevalence of mTOR activation in cancer has led to the development of two classes of inhibitors of the protein as therapeutics: the natural product rapamycin and its analogs as well as direct inhibitors of mTOR kinase. mTOR exists in at least two multi-protein complexes. The mTORC1 complex phosphorylates S6K and 4EBP and stimulates protein translation, metabolism as well as other processes. The mTORC2 complex phosphorylates and activates AKT and other AGC kinases. Rapamycin binds to the immunophilin FKBP12. Drug-bound FKBP12 complex binds to mTOR FRB domain and selectively inhibits the activity of mTORC1. However, rapalogs preferentially inhibit S6K phosphorylation compared to 4EBP phosphorylation. Rapalogs have undergone extensive clinical testing and have significant antitumor activity in renal cell and pancreatic neuroendocrine tumors and, in combination with aromatase inhibitors, in resistant, ER positive breast cancers. In contrast, mTOR kinase inhibitors suppress both mTORC1 and mTORC2 functions and potently inhibit S6K, 4EBP and AKT S473 phosphorylation. These drugs are in early clinical testing.

In order to better understand the mechanism of action of these drugs and potential mechanisms of tumor escape from mTOR inhibition, we selected breast tumor cells for resistance to growth inhibition in cell culture by treatment with either rapamycin or an mTOR kinase inhibitor. In rapamycin resistant cells, phosphorylation of S6K and S6 were insensitive to the drug, but remained sensitive to mTOR kinase inhibitors. Conversely, in clones resistant to mTOR kinase inhibitors, mTORC1 and mTORC2 substrates were insensitive to the drugs, but S6K and S6 phosphorylation remained sensitive to rapamycin. Deep sequencing results explained these findings: rapamycin resistant clones harbored mutations in the FRB domain of mTOR, in the sites shown to interact with the FKBP12-rapamycin complex; mTOR kinase resistant clones harbored mutations in the mTOR catalytic domain. These mutations were not observed in the parental cells. It is likely that the mutations identified in each domain prevent binding of the drug.

Consistent with these data, growth of rapamycin resistant cells retain sensitivity to mTOR kinase inhibitors and mTOR kinase resistant cells retain sensitivity to rapalogs, both in tissue culture and in vivo. The results suggest that tumor cells with acquired resistance to mTOR inhibitors retain a requirement for mTOR signaling for proliferation. Furthermore, tumors resistant to either class of drug may not be cross-resistant to the other and combined therapy with both might delay the onset of resistance. Further studies on the genetics of human tumors with acquired resistance to these agents will determine the clinical importance of these findings.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr PD1-8.

Novel techniques of preparing TEM samples for characterization of irradiation damage

Focus ion beam preparation of transmission electron microscopy (TEM) samples has become increasingly popular due to the relative ease of extraction of TEM foils from specific locations within a larger sample. However the sputtering damage induced by Ga ion bombardment in focus ion beam means that traditional electropolishing may be a preferable method. First, we describe a special electropolishing method for the preparation of irregular TEM samples from ex-service nuclear reactor components, spring-shaped spacers. This method has also been used to prepare samples from a nonirradiated component for a TEM in situ heavy ion irradiation study. Because the specimen size is small (0.7 × 0.7 × 3 mm), a sandwich installation is adopted to obtain high quality polishing. Second, we describe some modifications to a conventional TEM cross-section sample preparation method that employs Ni electroplating. There are limitations to this method when preparing cross-section samples from either (1) metals which are difficult to activate for electroplating, or (2) a heavy ion irradiated foil with a very shallow damage layer close to the surface, which may be affected by the electroplating process. As a consequence, a novel technique for preparing cross-section samples was developed and is described.

A step-by-step guide to the systematic review and meta-analysis of diagnostic and prognostic test accuracy evaluations

In evidence-based medicine (EBM), systematic reviews and meta-analyses have been widely applied in biological and medical research. Moreover, the most popular application of meta-analyses in this field may be to examine diagnostic (sensitivity and specificity) and prognostic (hazard ratio (HR) and its variance, standard error (SE) or confidence interval (CI)) test accuracy. However, conducting such analyses requires not only a great deal of time but also an advanced professional knowledge of mathematics, statistics and computer science. Regarding the practical application of meta-analyses for diagnostic and prognostic markers, the majority of users are clinicians and biologists, most of whom are not skilled at mathematics and computer science in particular. Hence, it is necessary for these users to have a simplified version of a protocol to help them to quickly conduct meta-analyses of the accuracy of diagnostic and prognostic tests. The aim of this paper is to enable individuals who have never performed a meta-analysis to do so from scratch. The paper does not attempt to serve as a comprehensive theoretical guide but instead describes one rigorous way of conducting a meta-analysis for diagnostic and prognostic markers. Investigators who follow the outlined methods should be able to understand the basic ideas behind the steps taken, the meaning of the meta-analysis results obtained for diagnostic and prognostic markers and the scope of questions that can be answered with Systematic Reviews and Meta-Analyses (SRMA). The presented protocols have been successfully tested by clinicians without meta-analysis experience.

Parathyroid hormone-related protein inhibits DKK1 expression through c-Jun-mediated inhibition of β-catenin activation of the DKK1 promoter in prostate cancer

Prostate cancer (PCa)bone metastases are unique in that majority of them induce excessive mineralized bone matrix, through undefined mechanisms, as opposed to most other cancers that induce bone resorption. Parathyroid hormone-related protein (PTHrP) is produced by PCa cells and intermittent PTHrP exposure has bone anabolic effects, suggesting that PTHrP could contribute to the excess bone mineralization. Wnts are bone-productive factors produced by PCa cells, and the Wnt inhibitor Dickkopfs-1 (DKK1) has been shown to promote PCa progression. These findings, in conjunction with the observation that PTHrP expression increases and DKK1 expression decreases as PCa progresses, led to the hypothesis that PTHrP could be a negative regulator of DKK1 expression in PCa cells and, hence, allow the osteoblastic activity of Wnts to be realized. To test this, we first demonstrated that PTHrP downregulated DKK1 mRNA and protein expression. We then found through multiple mutated DKK1 promoter assays that PTHrP, through c-Jun activation, downregulated the DKK1 promoter through a transcription factor (TCF) response element site. Furthermore, chromatin immunoprecipitation (ChIP) and re-ChIP assays revealed that PTHrP mediated this effect through inducing c-Jun to bind to a transcriptional activator complex consisting of β-catenin, which binds the most proximal DKK1 promoter, the TCF response element. Together, these results demonstrate a novel signaling linkage between PTHrP and Wnt signaling pathways that results in downregulation of a Wnt inhibitor allowing for Wnt activity that could contribute the osteoblastic nature of PCa.

Analyses of FLG mutation frequency and filaggrin expression in isolated ichthyosis vulgaris (IV) and atopic dermatitis-associated IV

BACKGROUND

Ichthyosis vulgaris (IV; OMIM 146700) is a very common inherited skin disorder. Loss-of-function mutations in the filaggrin gene (FLG) have been identified as the cause of IV. In a previous study, we found that the percentage of FLG null mutations was lower in IV associated with atopic dermatitis (AD) than in IV not associated with AD (isolated IV). We speculated that some clinical manifestations of IV in patients with AD are not induced by FLG mutations.

OBJECTIVES

In order to clarify this issue, we collected 21 IV pedigrees, 33 patients with sporadic isolated IV and 116 patients with AD-associated IV to analyse FLG mutation frequency and filaggrin expression in isolated IV and AD-associated IV.

METHODS

A comprehensive sequencing of the FLG gene in all patients was performed using an overlapping polymerase chain reaction (PCR) strategy. We also studied the immunohistochemistry of profilaggrin/filaggrin protein expression in the skin and measured the mRNA expression using real-time PCR in seven patients, including one patient with IV harbouring the mutation c.3321delA, two patients with AD-associated IV harbouring c.3321delA and c.6834del5, and four patients with AD-associated IV without FLG mutations.

RESULTS

The percentage of mutations in the FLG gene was 74% and 43% in patients with isolated IV and patients with AD-associated IV, respectively. Immunohistochemical staining revealed that profilaggrin/filaggrin peptides were remarkably reduced in the epidermis of all the patients. All the patients with either AD or IV showed lower FLG mRNA expression compared with the normal control.

CONCLUSIONS

These results indicate that factors other than FLG gene mutations can downregulate profilaggrin/filaggrin expression, leading to the ichthyosiform phenotype in the context of AD.

Pool Boiling Heat Transfer Enhancement Through Nanostructures on Silicon Microchannels

Uniform silicon nanowires (SiNW) were successfully fabricated on the top, bottom, and sidewall surfaces of silicon microchannels by using a two-step electroless etching process. Different microchannel patterns with the channel width from 100 to 300 μm were first fabricated in a 10 mm × 10 mm silicon chip and then covered by SiNW with an average height of 10–20 μm. The effects of the microchannel geometry, micro/nano-hierarchical structures on pool boiling were studied and the bubble dynamics on different sample surfaces were compared. It was found that the combination of the micro/nanostructures promoted microbubble emission boiling under moderate heat fluxes, and yielded superior boiling heat transfer performance. At given wall superheats, the maximum heat flux of the microchannel with SiNW was improved by 120% over the microchannel-only surface, and more than 400% over a plain silicon surface. These results provide a new insight into the boiling mechanism for micro/nano-hierarchical structures and demonstrate their potential in improving pool boiling performance for microchannels.

Serum cytokeratin-19 measured by cyfra21-1 assay in patients with gastrointestinal and gynecologic malignancy

The serum fragment of cytokeratin 19 was measured in 130 patients with gastrointestinal, breast and gynecologic cancer and 62 patients with benign disease using CYFRA21-1 immunoradiometric assay. Patients with advanced cancer showed the highest level of serum CYFRA21-1. When the cut-off level was set at 2 ng/ml, 7 of 61 patients with earlier stage cancer were positive whereas 45 of 69 patients with advanced cancer had serum CYFRA21-1 levels over 2 ng/ml. In benign gastrointestinal and gynecologic diseases, 4 of 66 patients were positive. Retrospective evaluation revealed a good correlation between the serum CYFRA21-1 concentration and clinical course. CYFRA21-1 may be a useful tumor marker for monitoring of gastrointestinal and gynecologic malignancies.

RBB, a novel transcription repressor, represses the transcription of HDM2 oncogene

The p53 tumor suppressor is important in many aspects of cell biology. Tight regulation of p53 is thus imperative for maintaining cell homeostasis and preventing tumorigenesis. The stabilization and activity of p53 is primarily regulated by MDM2, which is encoded for by HDM2. However, how the expression and activity of MDM2 is regulated remains largely unknown. Here, we report a novel BTB and BEN domains-containing protein, RBB. We demonstrated that RBB is a novel transcriptional repressor binding specific DNA motif via a homodimer and interacting with the nucleosome remodeling and deacetylase (NuRD) complex. Genome wide transcription target analysis by ChIP sequencing revealed that RBB represses the transcription of a series of functionally important genes including HDM2. We showed that RBB recruits the NuRD complex to the internal promoter of HDM2 and inhibits the expression of MDM2 protein, leading to subsequent stabilization of tumor suppressor p53. Significantly, we showed that RBB suppresses cell proliferation and sensitizes cells to DNA damage-induced apoptosis. Our data indicate that RBB is a novel transcriptional repressor and an important regulator of p53 pathway.

PGC-1β mediates adaptive chemoresistance associated with mitochondrial DNA mutations

Primary mitochondrial dysfunction commonly leads to failure in cellular adaptation to stress. Paradoxically, however, nonsynonymous mutations of mitochondrial DNA (mtDNA) are frequently found in cancer cells and may have a causal role in the development of resistance to genotoxic stress induced by common chemotherapeutic agents, such as cis-diammine-dichloroplatinum(II) (cisplatin, CDDP). Little is known about how these mutations arise and the associated mechanisms leading to chemoresistance. Here, we show that the development of adaptive chemoresistance in the A549 non-small-cell lung cancer cell line to CDDP is associated with the hetero- to homoplasmic shift of a nonsynonymous mutation in MT-ND2, encoding the mitochondrial Complex-I subunit ND2. The mutation resulted in a 50% reduction of the NADH:ubiquinone oxidoreductase activity of the complex, which was compensated by increased biogenesis of respiratory chain complexes. The compensatory mitochondrial biogenesis was most likely mediated by the nuclear co-activators peroxisome proliferator-activated receptor gamma co-activator-1α (PGC-1α) and PGC-1β, both of which were significantly upregulated in the CDDP-resistant cells. Importantly, both transient and stable silencing of PGC-1β re-established the sensitivity of these cells to CDDP-induced apoptosis. Remarkably, the PGC-1β-mediated CDDP resistance was independent of the mitochondrial effects of the co-activator. Altogether, our results suggest that partial respiratory chain defects because of mtDNA mutations can lead to compensatory upregulation of nuclear transcriptional co-regulators, in turn mediating resistance to genotoxic stress.

HtrA2 deficiency causes mitochondrial uncoupling through the F₁F₀-ATP synthase and consequent ATP depletion

Loss of the mitochondrial protease HtrA2 (Omi) in mice leads to mitochondrial dysfunction, neurodegeneration and premature death, but the mechanism underlying this pathology remains unclear. Using primary cultures from wild-type and HtrA2-knockout mice, we find that HtrA2 deficiency significantly reduces mitochondrial membrane potential in a range of cell types. This depolarisation was found to result from mitochondrial uncoupling, as mitochondrial respiration was increased in HtrA2-deficient cells and respiratory control ratio was dramatically reduced. HtrA2-knockout cells exhibit increased proton translocation through the ATP synthase, in combination with decreased ATP production and truncation of the F1 α-subunit, suggesting the ATP synthase as the source of the proton leak. Uncoupling in the HtrA2-deficient mice is accompanied by altered breathing pattern and, on a cellular level, ATP depletion and vulnerability to chemical ischaemia. We propose that this vulnerability may ultimately cause the neurodegeneration observed in these mice.

Direct measurement of the Fermi energy in graphene using a double-layer heterostructure

We describe a technique which allows a direct measurement of the relative Fermi energy in an electron system by employing a double-layer heterostructure. We illustrate this method by using a graphene double layer to probe the Fermi energy as a function of carrier density in monolayer graphene, at zero and in high magnetic fields. This technique allows us to determine the Fermi velocity, Landau level spacing, and Landau level broadening. We find that the N=0 Landau level broadening is larger by comparison to the broadening of upper and lower Landau levels.

Mutations analysis in filaggrin gene in northern China patients with atopic dermatitis

BACKGROUND

Recently, we have reported filaggrin mutations (FLG) of atopic dermatitis in southern China. However, there have been few detailed reports of FLG mutations of patients with AD in northern China by now.

OBJECTIVES

The present aim was to establish the mutation spectrum of FLG gene in AD patients in northern China.

METHODS

A total of 339 cases met Hanifin and Rajka diagnostic criteria of AD were recruited. A comprehensive sequencing of the entire FLG coding region in these patients was conducted. All detected FLG null mutations were screened in a cohort of 301 normal controls.

RESULTS

Seven novel mutations (478insA, Q1070X, 4026delT, Q1712X, Q2397X, 7145del4 and 8001del4) and eleven reported mutations (3222del4, 3321delA, 4271delAA, S1515X, Q1790X, 5757del4, 6834del5, Q2417X, E2422X, 7945delA and K4671X) in AD were identified. Mutations 3321delA and K4671X were two of the most common mutations in AD. FLG null mutations were present in 26.0% of AD patients. FLG null alleles (compound genotypes) were significantly higher in AD (P < 0.001) than in the controls. The compound genotypes for all FLG variants were significantly associated with IV (P < 0.001) and palmar hyperlinearity (P < 0.001). The common mutation, K4671X, was significantly associated with AD-coexistent allergic rhinitis (P = 0.005).

CONCLUSIONS

Our study increases the total number of FLG mutations. We clearly demonstrated that FLG loss-of-function mutations were significantly associated with AD in northern China. The FLG null mutations in the Chinese population differed not only from that in the European population but also from that in sub-populations of Asians outside of the Chinese mainland.