Cell-to-cell communication--periodontal regeneration.

BACKGROUND Although regenerative treatment options are available, periodontal regeneration is still regarded as insufficient and unpredictable. AIM This review article provides scientific background information on the animated 3D film Cell-to-Cell Communication - Periodontal Regeneration. RESULTS Periodontal regeneration is understood as a recapitulation of embryonic mechanisms. Therefore, a thorough understanding of cellular and molecular mechanisms regulating normal tooth root development is imperative to improve existing and develop new periodontal regenerative therapies. However, compared to tooth crown and earlier stages of tooth development, much less is known about the development of the tooth root. The formation of root cementum is considered the critical element in periodontal regeneration. Therefore, much research in recent years has focused on the origin and differentiation of cementoblasts. Evidence is accumulating that the Hertwig's epithelial root sheath (HERS) has a pivotal role in root formation and cementogenesis. Traditionally, ectomesenchymal cells in the dental follicle were thought to differentiate into cementoblasts. According to an alternative theory, however, cementoblasts originate from the HERS. What happens when the periodontal attachment system is traumatically compromised? Minor mechanical insults to the periodontium may spontaneously heal, and the tissues can structurally and functionally be restored. But what happens to the periodontium in case of periodontitis, an infectious disease, after periodontal treatment? A non-regenerative treatment of periodontitis normally results in periodontal repair (i.e., the formation of a long junctional epithelium) rather than regeneration. Thus, a regenerative treatment is indicated to restore the original architecture and function of the periodontium. Guided tissue regeneration or enamel matrix proteins are such regenerative therapies, but further improvement is required. As remnants of HERS persist as epithelial cell rests of Malassez in the periodontal ligament, these epithelial cells are regarded as a stem cell niche that can give rise to new cementoblasts. Enamel matrix proteins and members of the transforming growth factor beta (TGF-ß) superfamily have been implicated in cementoblast differentiation. CONCLUSION A better knowledge of cell-to-cell communication leading to cementoblast differentiation may be used to develop improved regenerative therapies to reconstitute periodontal tissues that were lost due to periodontitis.

Alveolar bone regeneration in response to local application of calcitriol in vitamin D deficient rats

AIM Vitamin D deficiency is considered to diminish bone regeneration. Yet, raising the serum levels takes months. A topic application of the active vitamin D metabolite, calcitriol, may be an effective approach. Thus, it becomes important to know the effect of vitamin D deficiency and local application on alveolar bone regeneration. MATERIAL AND METHODS Sixty rats were divided into three groups; two vitamin depletion groups and a control group. Identical single defects (2 mm diameter) were created in the maxilla and mandible treated with calcitriol soaked collagen in one deficiency group while in the other two groups not. Histomorphometric analysis and micro CTs were performed after 1 and 3 weeks. Serum levels of 25(OH)D3 and PTH were determined. RESULTS Bone formation rate significantly increased within the observation period in all groups. Bone regeneration was higher in the maxilla than in the mandible. However, bone regeneration was lower in the control group compared to vitamin depletion groups, with no significant effects by local administration of calcitriol (micro CT mandible p = 0.003, maxilla p < 0.001; histomorphometry maxilla p = 0.035, mandible p = 0.18). CONCLUSION Vitamin D deficiency not necessarily impairs bone regeneration in the rat jaw and a single local calcitriol application does not enhance healing.

Efficiency of In Vitro Regeneration is Dependent on the Genotype and Size of Explant in Tef [Eragrostis tef (Zucc.) Trotter]

Tef [Eragrostis tef (Zucc.) Trotter] is the major cereal crop in the Horn of Africa particularly in Ethiopia where it is staple food for about 50 million people. Its resilience to extreme environmental conditions and high in nutrition makes tef the preferred crop among both farmers and consumers. The efficiency of in vitro regeneration plays significant role in the improvement of crops. We investigated the efficiency of regeneration in 18 tef genotypes (15 landraces and three improved varieties) using three sizes of immature embryos (small, intermediate and large) as an explant. In vitro regeneration was significantly affected by the genotype and the size of the immature embryo used as a donor. Intermediate-size immature embryos which were 101-350 µm long led to the highest percentage of regeneration. Interestingly, the three improved varieties presented very low regeneration efficiencies whereas the landrace Manyi resulted in consistently superior percentage of in vitro regeneration from all three sizes of explants. The findings of this work provide useful insight into the tef germplasm amenable for the regeneration technique which has direct application in techniques such as transformation. It also signifies the importance of using tef landraces instead of improved varieties for in vitro regeneration.

Plant regeneration directs changes in grassland composition after extreme drought: a 13-year study in southern Switzerland

1. The cover of plant species was recorded annually from 1988 to 2000 in nine spatially replicated plots in a species-rich, semi-natural meadow at Negrentino (southern Alps). This period showed large climatic variation and included the centennial maximum and minimum frequency of days with ≥ 10 mm of rain. 2. Changes in species composition were compared between three 4-year intervals characterized by increasingly dry weather (1988–91), a preceding extreme drought (1992–95), and increasingly wet weather (1997–2000). Redundancy analysis and anova with repeated spatial replicates were used to find trends in vegetation data across time. 3. Recruitment capacity, the potential for fast clonal growth and seasonal expansion rate were determined for abundant taxa and tested in general linear models (GLM) as predictors for rates of change in relative cover of species across the climatically defined 4-year intervals. 4. Relative cover of the major growth forms present, graminoids and forbs, changed more in the period following extreme drought than at other times. Recruitment capacity was the only predictor of species’ rates of change. 5. Following perturbation, re-colonization was the primary driver of vegetation dynamics. The dominant grasses, which lacked high recruitment from seed, therefore decreased in relative abundance. This effect persisted until the end of the study and may represent a lasting response to an extreme climatic event.

Enamel matrix derivative and bone grafts for periodontal regeneration of intrabony defects. A systematic review and meta-analysis

OBJECTIVE The aim of the present systematic review and meta-analysis was to assess the clinical efficacy of regenerative periodontal surgery of intrabony defects using a combination of enamel matrix derivative (EMD) and bone graft compared with that of EMD alone. MATERIALS AND METHODS The Cochrane Oral Health Group specialist trials, MEDLINE, and EMBASE databases were searched for entries up to February 2014. The primary outcome was gain of clinical attachment (CAL). Weighted means and forest plots were calculated for CAL gain, probing depth (PD), and gingival recession (REC). RESULTS Twelve studies reporting on 434 patients and 548 intrabony defects were selected for the analysis. Mean CAL gain amounted to 3.76 ± 1.07 mm (median 3.63 95 % CI 3.51-3.75) following treatment with a combination of EMD and bone graft and to 3.32 ± 1.04 mm (median 3.40; 95 % CI 3.28-3.52) following treatment with EMD alone. Mean PD reduction measured 4.22 ± 1.20 mm (median 4.10; 95 % CI 3.96-4.24) at sites treated with EMD and bone graft and yielded 4.12 ± 1.07 mm (median 4.00; 95 % CI 3.88-4.12) at sites treated with EMD alone. Mean REC increase amounted to 0.76 ± 0.42 mm (median 0.63; 95 % CI 0.58-0.68) at sites treated with EMD and bone graft and to 0.91 ± 0.26 mm (median 0.90; 95 % CI 0.87-0.93) at sites treated with EMD alone. CONCLUSIONS Within their limits, the present results indicate that the combination of EMD and bone grafts may result in additional clinical improvements in terms of CAL gain and PD reduction compared with those obtained with EMD alone. The potential influence of the chosen graft material or of the surgical procedure (i.e., flap design) on the clinical outcomes is unclear. CLINICAL RELEVANCE The present findings support the use of EMD and bone grafts for the treatment of intrabony periodontal defects.

Biomaterials for promoting periodontal regeneration in human intrabony defects: a systematic review

Intrabony periodontal defects are a frequent complication of periodontitis and, if left untreated, may negatively affect long-term tooth prognosis. The optimal outcome of treatment in intrabony defects is considered to be the absence of bleeding on probing, the presence of shallow pockets associated with periodontal regeneration (i.e. formation of new root cementum with functionally orientated inserting periodontal ligament fibers connected to new alveolar bone) and no soft-tissue recession. A plethora of different surgical techniques, often including implantation of various types of bone graft and/or bone substitutes, root surface demineralization, guided tissue regeneration, growth and differentiation factors, enamel matrix proteins or various combinations thereof, have been employed to achieve periodontal regeneration. Despite positive observations in animal models and successful outcomes reported for many of the available regenerative techniques and materials in patients, including histologic reports, robust information on the degree to which reported clinical improvements reflect true periodontal regeneration does not exist. Thus, the aim of this review was to summarize, in a systematic manner, the available histologic evidence on the effect of reconstructive periodontal surgery using various types of biomaterials to enhance periodontal wound healing/regeneration in human intrabony defects. In addition, the inherent problems associated with performing human histologic studies and in interpreting the results, as well as certain ethical considerations, are discussed. The results of the present systematic review indicate that periodontal regeneration in human intrabony defects can be achieved to a variable extent using a range of methods and materials. Periodontal regeneration has been observed following the use of a variety of bone grafts and substitutes, guided tissue regeneration, biological factors and combinations thereof. Combination approaches appear to provide the best outcomes, whilst implantation of alloplastic material alone demonstrated limited, to no, periodontal regeneration.

Wound models for periodontal and bone regeneration: the role of biologic research

The ultimate goals of periodontal therapy remain the complete regeneration of those periodontal tissues lost to the destructive inflammatory-immune response, or to trauma, with tissues that possess the same structure and function, and the re-establishment of a sustainable health-promoting biofilm from one characterized by dysbiosis. This volume of Periodontology 2000 discusses the multiple facets of a transition from therapeutic empiricism during the late 1960s, toward regenerative therapies, which is founded on a clearer understanding of the biophysiology of normal structure and function. This introductory article provides an overview on the requirements of appropriate in vitro laboratory models (e.g. cell culture), of preclinical (i.e. animal) models and of human studies for periodontal wound and bone repair. Laboratory studies may provide valuable fundamental insights into basic mechanisms involved in wound repair and regeneration but also suffer from a unidimensional and simplistic approach that does not account for the complexities of the in vivo situation, in which multiple cell types and interactions all contribute to definitive outcomes. Therefore, such laboratory studies require validatory research, employing preclinical models specifically designed to demonstrate proof-of-concept efficacy, preliminary safety and adaptation to human disease scenarios. Small animal models provide the most economic and logistically feasible preliminary approaches but the outcomes do not necessarily translate to larger animal or human models. The advantages and limitations of all periodontal-regeneration models need to be carefully considered when planning investigations to ensure that the optimal design is adopted to answer the specific research question posed. Future challenges lie in the areas of stem cell research, scaffold designs, cell delivery and choice of growth factors, along with research to ensure appropriate gingival coverage in order to prevent gingival recession during the healing phase.

Periodontal regeneration - furcation defects: a consensus report from the AAP Regeneration Workshop

BACKGROUND Treatment of furcation defects is a core component of periodontal therapy. The goal of this consensus report is to critically appraise the evidence and to subsequently present interpretive conclusions regarding the effectiveness of regenerative therapy for the treatment of furcation defects and recommendations for future research in this area. METHODS A systematic review was conducted before the consensus meeting. This review aims to evaluate and present the available evidence regarding the effectiveness of different regenerative approaches for the treatment of furcation defects in specific clinical scenarios compared with conventional surgical therapy. During the meeting, the outcomes of the systematic review, as well as other pertinent sources of evidence, were discussed by a committee of nine members. The consensus group members submitted additional material for consideration by the group in advance and at the time of the meeting. The group agreed on a comprehensive summary of the evidence and also formulated recommendations for the treatment of furcation defects via regenerative therapies and the conduction of future studies. RESULTS Histologic proof of periodontal regeneration after the application of a combined regenerative therapy for the treatment of maxillary facial, mesial, distal, and mandibular facial or lingual Class II furcation defects has been demonstrated in several studies. Evidence of histologic periodontal regeneration in mandibular Class III defects is limited to one case report. Favorable outcomes after regenerative therapy for maxillary Class III furcation defects are limited to clinical case reports. In Class I furcation defects, regenerative therapy may be beneficial in certain clinical scenarios, although generally Class I furcation defects may be treated predictably with non-regenerative therapies. There is a paucity of data regarding quantifiable patient-reported outcomes after surgical treatment of furcation defects. CONCLUSIONS Based on the available evidence, it was concluded that regenerative therapy is a viable option to achieve predictable outcomes for the treatment of furcation defects in certain clinical scenarios. Future research should test the efficacy of novel regenerative approaches that have the potential to enhance the effectiveness of therapy in clinical scenarios associated historically with less predictable outcomes. Additionally, future studies should place emphasis on histologic demonstration of periodontal regeneration in humans and also include validated patient-reported outcomes. CLINICAL RECOMMENDATIONS Based on the prevailing evidence, the following clinical recommendations could be offered. 1) Periodontal regeneration has been established as a viable therapeutic option for the treatment of various furcation defects, among which Class II defects represent a highly predictable scenario. Hence, regenerative periodontal therapy should be considered before resective therapy or extraction; 2) The application of a combined therapeutic approach (i.e., barrier, bone replacement graft with or without biologics) appears to offer an advantage over monotherapeutic algorithms; 3) To achieve predictable regenerative outcomes in the treatment of furcation defects, adverse systemic and local factors should be evaluated and controlled when possible; 4) Stringent postoperative care and subsequent supportive periodontal therapy are essential to achieve sustainable long-term regenerative outcomes.

Significant lethality following liver resection in A20 heterozygous knockout mice uncovers a key role for A20 in liver regeneration

Hepatic expression of A20, including in hepatocytes, increases in response to injury, inflammation and resection. This increase likely serves a hepatoprotective purpose. The characteristic unfettered liver inflammation and necrosis in A20 knockout mice established physiologic upregulation of A20 as integral to the anti-inflammatory and anti-apoptotic armamentarium of hepatocytes. However, the implication of physiologic upregulation of A20 in modulating hepatocytes' proliferative responses following liver resection remains controversial. To resolve the impact of A20 on hepatocyte proliferation and the liver's regenerative capacity, we examined whether decreased A20 expression, as in A20 heterozygous knockout mice, affects outcome following two-third partial hepatectomy. A20 heterozygous mice do not demonstrate a striking liver phenotype, indicating that their A20 expression levels are still sufficient to contain inflammation and cell death at baseline. However, usually benign partial hepatectomy provoked a staggering lethality (>40%) in these mice, uncovering an unsuspected phenotype. Heightened lethality in A20 heterozygous mice following partial hepatectomy resulted from impaired hepatocyte proliferation due to heightened levels of cyclin-dependent kinase inhibitor, p21, and deficient upregulation of cyclins D1, E and A, in the context of worsened liver steatosis. A20 heterozygous knockout minimally affected baseline liver transcriptome, mostly circadian rhythm genes. Nevertheless, this caused differential expression of >1000 genes post hepatectomy, hindering lipid metabolism, bile acid biosynthesis, insulin signaling and cell cycle, all critical cellular processes for liver regeneration. These results demonstrate that mere reduction of A20 levels causes worse outcome post hepatectomy than full knockout of bona fide liver pro-regenerative players such as IL-6, clearly ascertaining A20's primordial role in enabling liver regeneration. Clinical implications of these data are of utmost importance as they caution safety of extensive hepatectomy for donation or tumor in carriers of A20/TNFAIP3 single nucleotide polymorphisms alleles that decrease A20 expression or function, and prompt the development of A20-based liver pro-regenerative therapies.

The Role of Cells in Meniscal Guided Tissue Regeneration: A Proof of Concept Study in a Goat Model.

OBJECTIVE Successful repair of defects in the avascular zone of meniscus remains a challenge in orthopedics. This proof of concept study aimed to investigate a guided tissue regeneration approach for treatment of tears in meniscus avascular zone in a goat model. DESIGN Full-depth longitudinal tear was created in the avascular zone of the meniscus and sutured. In the two treatment groups, porcine collagen membrane was wrapped around the tear without (CM) or with injection of expanded autologous chondrocytes (CM+cells), whereas in the control group the tear remained only sutured. Gait recovery was evaluated during the entire follow-up period. On explantation at 3 and 6 months, macroscopic gross inspection assessed healing of tears, degradation of collagen membrane, potential signs of inflammation, and osteoarthritic changes. Microscopic histology scoring criteria were developed to evaluate healing of tears, the cellular response, and the inflammatory response. RESULTS Gait recovery suggested protective effect of collagen membrane and was supported by macroscopical evaluation where improved tear healing was noted in both treated groups. Histology scoring in CM compared to suture group revealed an increase in tear margins contact, newly formed connective tissue between margins, and cell formations surrounded with new matrix after 3 months yet not maintained after 6 months. In contrast, in the CM+cells group these features were observed after 3 and 6 months. CONCLUSIONS A transient, short-term guided tissue regeneration of avascular meniscal tears occurred upon application of collagen membrane, whereas addition of expanded autologous chondrocytes supported more sustainable longer term tear healing.

Immediate implant placement with simultaneous guided bone regeneration in the esthetic zone: 10-year clinical and radiographic outcomes.

AIM To associate the dimension of the facial bone wall with clinical, radiological, and patient-centered outcomes at least 10 years after immediate implant placement with simultaneous guided bone regeneration in a retrospective study. MATERIAL AND METHODS Primary endpoint was the distance from the implant shoulder (IS) to the first bone-to-implant contact (IS-BIC10y ). Secondary endpoints included the facial bone thickness (BT10y ) 2, 4, and 6 mm apical to the IS, and the implant position. At baseline, the horizontal defect width (HDWBL ) from the implant surface to the alveolar wall was recorded. At recall, distance from the IS to the mucosal margin (IS-MM10y ), degree of soft tissue coverage of the mesial and distal aspects of the implants (PISm10y , PISd10y ; Papilla Index), pocket probing depth (PPD10y ), and patient-centered outcomes were determined. Width of the keratinized mucosa (KM), Full-Mouth Plaque and Bleeding Score (FMPS, FMBS) were available for both time points. RESULTS Of the 20 patients who underwent immediate implant placement with simultaneous guided bone regeneration and transmucosal healing, nine males and eight females with a median age of 62 years (42 min, 84 max) were followed up for a median period of 10.5 y (min 10.1 max 11.5). The 10-year implant survival rate was 100%. Multivariate regression analysis revealed a correlation of the IS-BIC10y , controlled for age and gender, with four parameters: HDWBL (P = 0.03), KMBL -10 (P = 0.02), BT10 4 mm (P = 0.01), and BT10 6 mm (P = 0.01). CONCLUSION Within the conditions of the present study, the horizontal defect width was the main indicator for the vertical dimension of the facial bone. The facial bone dimension was further associated with a reduction in the width of the keratinized mucosa and the dimension of the buccal bone.

P2X1 regulated IL-22 secretion by innate lymphoid cells is required for efficient liver regeneration.

Paracrine signalling mediated via cytokine secretion is essential for liver regeneration after hepatic resection, yet the mechanisms of cellular crosstalk between immune and parenchymal cells are still elusive. Interleukin-22 (IL-22) is released by immune cells and mediates strong hepatoprotective functions. However, it remains unclear if IL-22 is critical for the crosstalk between liver lymphocytes and parenchymal cells during liver regeneration after partial hepatectomy. Here we found that plasma levels of IL-22 and its upstream cytokine IL-23 are highly elevated in patients after major liver resection. In a mouse model of partial hepatectomy, deletion of IL-22 was associated with significantly delayed hepatocellular proliferation and an increase of hepatocellular injury and endoplasmic reticulum stress. Using Rag1-/- and Rag2-/- γc-/- mice we show that the main producers of IL-22 post partial hepatectomy are conventional natural killer cells and innate lymphoid cells type 1. Extracellular ATP, a potent danger molecule, is elevated in patients immediately after major liver resection. Antagonism of the P2 type nucleotide receptors P2X1 and P2Y6 significantly decreased IL-22 secretion ex vivo. In vivo, specific inhibition of P2X1 was associated with decreased IL-22 secretion, elevated liver injury and impaired liver regeneration.

Telomerase Is Essential for Zebrafish Heart Regeneration.

After myocardial infarction in humans, lost cardiomyocytes are replaced by an irreversible fibrotic scar. In contrast, zebrafish hearts efficiently regenerate after injury. Complete regeneration of the zebrafish heart is driven by the strong proliferation response of its cardiomyocytes to injury. Here we show that, after cardiac injury in zebrafish, telomerase becomes hyperactivated, and telomeres elongate transiently, preceding a peak of cardiomyocyte proliferation and full organ recovery. Using a telomerase-mutant zebrafish model, we found that telomerase loss drastically decreases cardiomyocyte proliferation and fibrotic tissue regression after cryoinjury and that cardiac function does not recover. The impaired cardiomyocyte proliferation response is accompanied by the absence of cardiomyocytes with long telomeres and an increased proportion of cardiomyocytes showing DNA damage and senescence characteristics. These findings demonstrate the importance of telomerase function in heart regeneration and highlight the potential of telomerase therapy as a means of stimulating cell proliferation upon myocardial infarction.