Increased bone inflammation in type 2 diabetes and obesity correlates with Wnt signaling downregulation and reduced bone strength
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eLife Assessment
This is a convincing paper that addresses topics important in our understanding of how inflammatory markers are modulated in both obesity and type 2 diabetes and their effects on Wnt signaling mediators in human bone. There are changes in bone at the tissue level in these 2 common metabolic disorders that ultimately lead to compromised bone strength. These data will be critical to our understanding of the pathophysiology of skeletal fragility in obesity and diabetes.
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Abstract
Type 2 diabetes (T2D) and obesity (OB) are associated with chronic low-grade inflammation and increased fracture risk. In vitro studies showed that inflammation induces bone erosion and inhibits bone formation by increasing Wnt canonical pathway inhibitors. However, the impact of inflammation on Wnt pathway regulation and bone quality in T2D and OB remains unclear. To this end, we studied 63 postmenopausal women (age >65 years) undergoing hip replacement for osteoarthritis. Among these women, 19 had T2D and OB (HbA1c 6.8±0.79%; BMI 29.9±5.2 kg/m2), 17 had OB but they were normoglycemic (BMI 32.5±5.4 kg/m2), and 27 served as controls (BMI 23.1±5.5 kg/m2). Serum inflammatory cytokines by automated immunoassay (ELLA), revealed higher TNF-α (p=0.0084) and lower adiponectin (p=0.0402) in T2D, and higher IL-6 (p=0.0003) levels in OB vs controls. Gene expression analysis of trabecular bone showed increased TNF-α (p=0.0019) and SFRP5 (p=0.0084) in T2D vs controls. IL-10 was lower in both T2D (p=0.0285), and OB (p=0.0324), while adiponectin (ADIPOQ) was only lower in T2D (p=0.0041) vs controls. Interestingly, the Wnt inhibitor SOST was higher in T2D (p<0.0001) and OB (p<0.0001) vs controls. Conversely, WNT10B mRNA levels were lower in T2D (p=0.0071) and in OB (p=0.0196) vs controls, while LEF-1 were only lower in T2D (p=0.0009). WNT5A (p=0.0025) and GSK3β (p=0.0003) mRNA levels were higher only T2D vs controls. Importantly, TNF-α mRNA levels positively correlated with SOST (r=0.5121, p=0.0002), WNT5A (r=0.3227, p=0.0396) and GSK3β (r=0.3789, p=0.0146) mRNA levels, but negatively correlated with WNT10B (r=0.3844, p=0.0188) and LEF-1(r=-0.3310, p=0.0322) mRNA levels. Conversely, IL-10 was negatively correlated with SOST mRNA levels (r=0.3100, p=0.0457). ADIPOQ was negatively correlated with SOST (r=-0.3864, p=0.0105) and WNT5A (r=-0.3025, p=0.0515) mRNA levels. Moreover, SFRP5 was negatively correlated with LEF-1 mRNA levels (r=0.3991, p=0.0131). Finally, serum levels of TNF-α (r=-0.3473, p=0.0352) and IL-6 (r=-0.3777, p=0.0302) negatively correlated with Young’s Modulus, an index of bone strength. These findings suggest that increased inflammation in bone of subjects with T2D and obesity is negatively associated with Wnt pathway and bone strength, shedding light on pathophysiology of bone impairment in T2D and obesity.
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eLife Assessment
This is a convincing paper that addresses topics important in our understanding of how inflammatory markers are modulated in both obesity and type 2 diabetes and their effects on Wnt signaling mediators in human bone. There are changes in bone at the tissue level in these 2 common metabolic disorders that ultimately lead to compromised bone strength. These data will be critical to our understanding of the pathophysiology of skeletal fragility in obesity and diabetes.
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Reviewer #1 (Public review):
This is a well-done clinical study which provides new information on the effects of metabolic disturbances in the human skeleton. 63 postmenopausal women undergoing hip arthroplasty, consisting of T2D with obesity; obesity alone; and neither T2D nor obesity were studied. Most of the findings relate to T2D. Increased serum TNF-α was found in T2D, as well as increased bone gene expression of TNF- α, which was associated with reduced expression of Wnt pathway genes. mRNA levels of certain of the cytokines correlated with Wnt signaling components. In addition, the increased serum TNF- α in T2D was associated with reduced Young's modulus, a measure of bone strength. A strength of this paper is that it provides information in an area that is not well-understood. However, there are a number of concerns that warrant …
Reviewer #1 (Public review):
This is a well-done clinical study which provides new information on the effects of metabolic disturbances in the human skeleton. 63 postmenopausal women undergoing hip arthroplasty, consisting of T2D with obesity; obesity alone; and neither T2D nor obesity were studied. Most of the findings relate to T2D. Increased serum TNF-α was found in T2D, as well as increased bone gene expression of TNF- α, which was associated with reduced expression of Wnt pathway genes. mRNA levels of certain of the cytokines correlated with Wnt signaling components. In addition, the increased serum TNF- α in T2D was associated with reduced Young's modulus, a measure of bone strength. A strength of this paper is that it provides information in an area that is not well-understood. However, there are a number of concerns that warrant direct addressing.
(1) Can the authors speculate why the changes in cytokines and Wnt expression do not impact bone microarchitecture?
(2) The authors state that they are showing an association between inflammation and bone strength via the regulation of Wnt signaling. However they have only shown here that serum cytokines correlate with bone strength. It is true that the authors have previously shown that Wnt signaling correlated with bone strength. But here it would be useful to show if bone strength is also correlated with inflammatory genes.
(3) AGEs increase inflammation (by binding to RAGE which triggers an inflammatory cascade). AGEs might also increase SOST. From their previous work, it seems that the authors have bone AGE measures on these patients and they have shown their relationship with SOST. Do the increased AGEs relate to inflammation as measured by serum and bone expression?
(4) Were bone turnover markers done to show how the inflammation and Wnt findings relate to bone resorption and formation?
(5) RNA integrity values should be reported to confirm that the RNA has not degraded.
(6) The discussion of adiponectin could be clearer (studies are cited that show both positive and negative effects). Please clarify that adiponectin effects on bone are complex and what they are.
(7) Were patients excluded for prior as well as current antiresorptive medication use?
(8) Fig 4A. correlation between SOST mRNA and TNF-a mRNA seems to be driven by 1 outlier. Does the relationship persist if it is removed?
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Reviewer #2 (Public review):
Summary:
Chronic inflammation of the bone microenvironment conferred by T2DM and obesity may inhibit bone formation and bone strength by decreasing the ratio of Wnt ligands/Wnt inhibitors.
The authors studied 63 postmenopausal women (age >65 years) undergoing hip replacement for osteoarthritis. These were grouped into T2DM and obesity, obesity only, and normal subjects. A set of inflammatory markers was measured in the serum and gene expression of members of the Wnt system in the bone tissue. Bone samples were assessed by micro-CT.
While TNF-α serum levels were higher in T2DM, IL-6 levels were higher in obesity as compared to control. In the bone compartment the most consistent finding was decreased mRNA levels for WNt10b and increased sclerostin mRNA levels, translating into a suppressed Wnt-to-Wnt …
Reviewer #2 (Public review):
Summary:
Chronic inflammation of the bone microenvironment conferred by T2DM and obesity may inhibit bone formation and bone strength by decreasing the ratio of Wnt ligands/Wnt inhibitors.
The authors studied 63 postmenopausal women (age >65 years) undergoing hip replacement for osteoarthritis. These were grouped into T2DM and obesity, obesity only, and normal subjects. A set of inflammatory markers was measured in the serum and gene expression of members of the Wnt system in the bone tissue. Bone samples were assessed by micro-CT.
While TNF-α serum levels were higher in T2DM, IL-6 levels were higher in obesity as compared to control. In the bone compartment the most consistent finding was decreased mRNA levels for WNt10b and increased sclerostin mRNA levels, translating into a suppressed Wnt-to-Wnt inhibitor ratio, which was associated with low bone strength.
Strengths:
The study includes clinically well-characterized subjects of three defined subgroups. The analyses were comprehensive.
Weaknesses:
Including data or information on the Wnt inhibitor Dkk1 would be instructive. Analysis were limited to mRNA studies. Validation of protein levels would be supportive (although technically challenging).
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Reviewer #3 (Public review):
In this manuscript, the authors examine circulating and bone parameters in patients with T2DM or obesity vs control subjects. Based on their findings they conclude that increased inflammation in bone of subjects with T2DM and obesity is negatively correlated with Wnt pathway signaling and bone strength.
Overall, this is a well done clinical study that provides further insights into the pathogenesis of bone loss associated with T2DM. However, there are a number of issues that the authors should address:
(1) The major conceptual problem is that the alterations in circulating and bone factors they observed would predominantly affect bone turnover and thus, bone mass. But bone mass is preserved in T2DM (as their own data show). They postulate that their findings lead to impaired bone quality, but it is not clear …
Reviewer #3 (Public review):
In this manuscript, the authors examine circulating and bone parameters in patients with T2DM or obesity vs control subjects. Based on their findings they conclude that increased inflammation in bone of subjects with T2DM and obesity is negatively correlated with Wnt pathway signaling and bone strength.
Overall, this is a well done clinical study that provides further insights into the pathogenesis of bone loss associated with T2DM. However, there are a number of issues that the authors should address:
(1) The major conceptual problem is that the alterations in circulating and bone factors they observed would predominantly affect bone turnover and thus, bone mass. But bone mass is preserved in T2DM (as their own data show). They postulate that their findings lead to impaired bone quality, but it is not clear how this would occur. For example, the impairment in bone quality could be due to the accumulation of AGEs in bone in T2DM, and the correlations observed be true but unrelated. Along these lines, were serum or bone AGEs measured - and if not, is it possible for the authors to do so? At the least, this issue should be fully addressed in the Discussion if the authors are unable to provide additional data to address this.
(2) The T2DM patients were extremely well controlled. This may have limited some of the differences between groups. Was it not possible to select a group of less well-controlled patients - that is more the norm? This may also explain why the biomechanical indices in Table 3 were only marginally different in the T2DM vs the other groups. This point should also be addressed.
(3) The authors found some interesting differences in bone sclerostin levels. Were circulating sclerostin levels measured? This data would be of interest and should be provided.
(4) Fig 4A - the correlation between TNFa and SOST seems to be driven by one highly influential point. What happens if this point is removed? Is this point a formal statistical outlier? Please check this.
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