[Leptin: a link between obesity and osteoarthritis?]

The role of leptin in osteoarthritis

BACKGROUND

The pathogenesis of osteoarthritis (OA) is not clear; leptin may be related to its pathogenesis.

METHODS

We reviewed articles on leptin in OA, chondrocytes, and in vitro experiments. It is concluded that leptin may lead to OA via some signaling pathways. At the same time, the concentration of leptin in vitro experiments and OA/rheumatoid arthritis (RA) patients was summarized.

RESULTS

Leptin levels in serum and synovial fluid of OA/RA patients were higher than normal person. In the condition of infection and immunity, serum leptin levels in the peripheral blood significantly increase. Because of the close relationship between obesity, leptin, and OA, it is crucial to study the effects of weight loss and exercise intervention on serum leptin levels to improve the symptoms of OA patients.

CONCLUSION

Treatment for leptin-increased obesity may be a treatment for OA. The role of leptin in OA cannot be ignored and needs to be further studied.

Microarray study of gene expression profile to identify new candidate genes involved in the molecular mechanism of leptin-induced knee joint osteoarthritis in rat

BACKGROUND

Osteoarthritis (OA) is one of the most prevalent chronic joint diseases while the precise genetic mechanism remains elusive. In this study, we investigated the gene expression profile in OA by microarray analysis.

RESULTS

Histopathological characteristics of OA cartilage were examined using a rat model of leptin-induced OA. Gene expression profile of leptin-induced articular cartilage and healthy rat cartilage were compared using genome-wide microarray hybridization. A total of 1857 genes differentially expressed genes (1197 upregulated and 660 downregulated) were identified, some of which are known to be associated with leptin-induced OA phenotype. These included genes related to MMPs, inflammatory factors, growth factors, apoptotic genes and osteogenic genes. In addition, upregulated expressions of some new candidate genes, which have hitherto fore not been linked to OA (such as BCL2L11) were detected in leptin-induced OA cartilage, which suggests that these genes might be important for OA molecular mechanism.

CONCLUSION

Our findings suggest that pathogenesis of leptin-induced OA involves modulation of expression of multiple genes, although the underlying molecular mechanisms need to be studied further. Further investigation of leptin-induced gene expression changes is needed to gain new insights into the molecular mechanism of OA pathogenesis.

IL-6 secretion in osteoarthritis patients is mediated by chondrocyte-synovial fibroblast cross-talk and is enhanced by obesity

Increasing evidence suggests that inflammation plays a central role in driving joint pathology in certain patients with osteoarthritis (OA). Since many patients with OA are obese and increased adiposity is associated with chronic inflammation, we investigated whether obese patients with hip OA exhibited differential pro-inflammatory cytokine signalling and peripheral and local lymphocyte populations, compared to normal weight hip OA patients. No differences in either peripheral blood or local lymphocyte populations were found between obese and normal-weight hip OA patients. However, synovial fibroblasts from obese OA patients were found to secrete greater amounts of the pro-inflammatory cytokine IL-6, compared to those from normal-weight patients (p < 0.05), which reflected the greater levels of IL-6 detected in the synovial fluid of the obese OA patients. Investigation into the inflammatory mechanism demonstrated that IL-6 secretion from synovial fibroblasts was induced by chondrocyte-derived IL-6. Furthermore, this IL-6 inflammatory response, mediated by chondrocyte-synovial fibroblast cross-talk, was enhanced by the obesity-related adipokine leptin. This study suggests that obesity enhances the cross-talk between chondrocytes and synovial fibroblasts via raised levels of the pro-inflammatory adipokine leptin, leading to greater production of IL-6 in OA patients.

Metabolic syndrome increases the prevalence of spine osteoarthritis

OBJECTIVE

To determine whether the prevalence of severe spinal osteoarthritis (OA) increases with the number of metabolic syndrome (MetS) risk factors.

METHODS

Data from a single surgeon's high volume, spine surgery practice were reviewed. Severe OA was defined as degenerative spondylolisthesis or cervical or lumbar stenosis causing neurologically based symptoms and early OA as lumbar and cervical spondylosis causing axial pain only. Logistic regression modeling was used to determine the odds (adjusted for age and sex) of having severe spine OA with more numerous MetS risk factors.

RESULTS

Severe spinal OA was identified in 839/1502 patients (55.9%) and early OA in the remaining 663 individuals (44.1%). The overall prevalence of MetS was 30/1502 (2.0%): 26/839 (3.1%) in the severe OA group and 4/663 (0.6%) in the early OA group (P = 0.001). Presence of all four MetS risk factors was associated with almost quadruple the odds of having severe OA as compared with absence of risk factors (OR 3.9 [1.4-11.6], P < 0.01).

CONCLUSION

The components of MetS are more prevalent in subjects with severe spinal OA than in those with spondylosis causing axial pain. Future study of the association between MetS and the incidence of OA is required.

Multiple sclerosis and the role of immune cells

Multiple sclerosis (MS) is a complex disease with many different immune cells involved in its pathogenesis, and in particular T cells as the most recognized cell type. Recently, the innate immune system has also been researched for its effect on the disease. Hence, cells of the immune system play vital roles in either ameliorating or exacerbating the disease. The genetic and environmental factors, as well as the etiology and pathogenesis are of utmost importance for the development of MS. An insight into the roles play by T cells, B cells, natural killer cells, and dendritic cells in MS and the animal model experimental autoimmune encephalomyelitis, will be presented. Understanding the mechanisms of action for current therapeutic modalities should help developing new therapeutic tools to treat this disease and other autoimmune diseases.

Effect of total knee arthroplasty on type II diabetes mellitus and hypertension: A prospective study

CONTEXT

Advanced osteoarthritis of knee joint if bilateral, severely restricts patient mobility. This acts as an aggravating factor for pre existing comorbid elements of metabolical syndrome (MS) like Type II diabetes mellitus and hypertension as patients are unable to carry out therapeutic walks. Successfully implanted total knee arthroplasty (TKA) increases physical activity and enables to carry out therapeutic walks thus may help in better control of type II diabetes mellitus and hypertension. The objective of this prospective study was to find whether TKA for osteoarthritis knee had any effect to improve blood glucose levels and reduce blood pressure.

MATERIALS AND METHODS

A prospective study was done in which patients operated for tricompartmental osteoarthritis of knee with associated comorbidities like Type II diabetes mellitus or hypertension during a period of 2008 and 2009 were studied. One hundred and twenty patients were enrolled (55 diabetics, 65 hypertensives) who met our inclusion criteria. Preoperative knee society score, lower extremity activity scale fasting blood glucose level and systolic and diastolic blood pressure were compared with one year followup values. The KSS and LEAS scores were analysed by the Wilcoxon signed ranked test, while the fasting blood glucose (FBG) levels and systolic and diastolic blood pressure levels were analysed by paired 't' test.

RESULTS

The reduction of systolic blood pressure by 8 mmHg (t = 5.6, P value < 0.05) and diastolic blood pressure by 6 mmHg (t = 7.6, P value < 0.05) was recorded which was statistically significant. However, no statistically significant effect on fasting blood glucose levels was observed (t = -0.77, P value = 0.442). KSS improved in DM from preoperative 29 to 86 and LEAS improved from 6.7 to 11.3.

CONCLUSIONS

Authors are of the opinion that successful total knee replacement results in increased physical activity and reduces blood pressure (systolic and diastolic) in hypertensives. However, the same is not seen in blood glucose level. Increased physical activity and reduced dependence on NSAIDS postoperatively, may be contributing in reduction of systolic and diastolic blood pressure. Further studies in this aspect are necessary.

Leptin receptor JAK2/STAT3 signaling modulates expression of Frizzled receptors in articular chondrocytes

OBJECTIVE

Differentiated articular chondrocytes express a functional bisoform of the leptin receptor (LRb); however, leptin-LRb signaling in these cells is poorly understood. We hypothesized that leptin-LRb signaling in articular chondrocytes functions to modulate canonical Wnt signaling events by altering the expression of Frizzled (FZD) receptors.

METHODS

Human chondrocyte cell lines and primary articular chondrocytes were grown in serum containing growth media for 24h, followed by a media change to Dulbecco's modified Eagle's medium (DMEM) containing 1% Nutridoma-SP to obtain a serum-deficient environment for 24h before treatment. Treatments included recombinant human leptin (10-100nM), recombinant human IL-6 (0.3-3nM), or recombinant human erythropoietin (Epo) (10mU/ml). Cells were harvested 30min-48h after treatment and whole cell lysates were analyzed using immunoblots or luciferase assays.

RESULTS

Treatment of cells with leptin resulted in activation of Janus kinase 2 (JAK2) and subsequent phosphorylation of specific tyrosine residues on LRb, followed by dose- and time-dependent increases in the expression of Frizzled-1 (FZD1) and Frizzled-7 (FZD7). Leptin-mediated increases in the expression of FZD1 were blocked by pre-treatment with the protein synthesis inhibitor cycloheximide or the JAK2 inhibitor AG490. Experiments using a series of hybrid Epo extracellular domain-leptin intracellular domain receptors (ELR) harboring mutations of specific tyrosine residues in the cytoplasmic tail showed that increases in the expression of FZD1 were dependent on LRb-mediated phosphorylation of STAT3, but not ERK1/2 or STAT5. Leptin pre-treatment of chondrocytes prior to Wnt3a stimulation resulted in an increased magnitude of canonical Wnt signaling.

CONCLUSION

These experiments show that leptin-LRb signaling in articular chondrocytes modulates expression of canonical Wnt signaling receptors and suggests that direct cross-talk between these pathways is important in determining chondrocyte homeostasis.