Inflammatory and diabetic conditions trigger SHP2 tyrosine phosphatase expression and subsequent aberrant activation of primary human monocytes

Purpose

Atherosclerosis is an inflammatory process that is particularly accelerated in diabetics, leading to increased incidence of cardiovascular diseases such as CAD and PAD in diabetic patients. Monocytes are the main component of atherosclerosis development. SHP-2 tyrosine phosphatase has been identified as an important regulator of monocyte function. The present study therefore aims to investigate the regulation of SHP-2 in inflammatory and diabetic conditions.

Methods

Primary human monocytes were isolated from the peripheral blood of type 2 Diabetes mellitus (T2DM) patients and healthy individuals. Monocytes were incubated with pro-inflammatory cytokine TNFa. For diabetic conditions, monocytes were incubated with methylglyoxal (MG), a highly reactive side product of glycolysis, or Receptor for advanced glycation end product (RAGE) ligand AGE-bovine serum (AGE-BSA). Monocyte migration was studied with Transwell migration assays. Expression of important molecules was investigated with Western Blot, RT-qPCR or FACS. Pharmacological inhibitors for SHP2, RAGE or NFκB were used.

Results

First, we could detect a significant correlation between SHP-2 mRNA and TNFa levels in T2DM monocytes in comparison to monocytes from healthy individuals. In line with that, incubation of monocytes with TNFa lead to an enhanced expression of SHP-2. Co-incubation with NFκB-inhibitor blocked TNFa-induced SHP-2 upregulation. Interestingly, incubation of monocytes with methylglyoxal caused increased release of TNFa and also augmented expression of SHP-2, indicating a pro-inflammatory effect of diabetic conditions.

Moreover, AGE-BSA treatment induced enhanced SHP-2 expression, reflecting an inflammatory-independent pathway which regulates SHP-2 additionally. This could be supported by the observation that pharmacological inhibition of RAGE attenuated both AGE-BSA and MG-induced SHP-2 activation. On a functional level, increased expression of SHP-2 in each treatment resulted in a pro-migratory phenotype that could be completely reversed by inhibition of RAGE, respectively. Fittingly, monocytes from T2DM patients showed increased migration, which normalized to an ordinary level after application of a SHP-2 inhibitor.

Conclusions

The present results reveal a new mechanism for accelerated atherosclerosis development in diabetic patients. MG and advanced glycated end products, as crucial components of the diabetic milieu, lead to increased expression of SHP-2 via the RAGE-NFkB signalling axis. Interestingly, this diabetic environment causes an increased inflammatory response through the release of TNFa cytokine, which itself leads to enhanced SHP-2 expression through activation of the NFkB transcription factor. Finally, by pharmacological inhibition of each component in this outlined SHP-2 regulatory pathway, we were able to prevent the pro-migratory activation of monocytes, offering a new approach to the treatment of diabetes-induced atherosclerosis.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): IZKF SEED Project 14/20

Induction of RAGE-NFkB signalling axis enhances SHP-2 tyrosine phosphatase expression resulting in deviant activation of diabetic monocytes

Purpose

Aberrant activation of Type 2 Diabetes mellitus (T2DM) monocytes is an important pathomechanism leading to restricted arteriogenesis and augmented atherosclerosis, hereby, accelerating CAD and PAD. Tyrosine phosphatase SHP-2 was found to be upregulated in T2DM-monocytes. This study aimed to identify the pathways regulating SHP-2 expression in T2DM-monocytes.

Methods

Primary human monocytes were isolated from the peripheral blood of T2DM patients and healthy individuals. Monocytes were incubated with Methylglyoxal (MG), a highly reactive side product of glycolysis, Receptor for advanced glycation end product (RAGE) ligand AGE-bovine serum (AGE-BSA) or TNFα for 24 hours. Transwell migration assays were used to analyse the migratory potential of monocytes. Western Blot, RT-qPCR and FACS were performed to quantify the expression of relevant molecules. Pharmacological inhibitors were used to study functional relevance of the RAGE-NFκB-SHP-2 signalling axis.

Results

Significantly enhanced SHP-2 expression was detected in monocytes, which were incubated with TNFα, MG or AGE-BSA, respectively. Co-incubation of these molecules with NFκB-inhibitor blocked SHP-2 upregulation. Pharmacological inhibition of RAGE reversed the MG or AGE-BSA induced SHP-2 expression and activity in monocytes. RAGE expression on monocytes was upregulated after the incubation with MG or AGE-BSA, consistent with enhanced RAGE mRNA levels in T2DM monocytes. Besides, we also detected elevated SHP-2 transcripts in monocytes of T2DM patients which was more pronounced in monocytes with augmented TNFα expression. Furthermore, MG and AGE-BSA provoked the enhanced migration of monocytes which could be significantly reduced after the application of an allosteric SHP-2 inhibitor. Interestingly, pharmacological inhibition of RAGE in these conditions alone was sufficient to block the elevated monocyte migration. Moreover, monocytes isolated from T2DM patients revealed a comparable pro-migratory phenotype, which was completely restored after the pharmacological inhibition of SHP-2.

Conclusions

This study identified the upstream signalling mediators that contribute to SHP-2 dependent monocyte activation in T2DM conditions. Glucose metabolite (MG) or RAGE ligand (AGE-BSA) alone were sufficient to induce a pro-migratory phenotype in monocytes by upregulating SHP-2. Of note, an inflammatory state seems to accelerate this effect since enhanced TNFα levels were found to be positively correlated with the augmented SHP-2 expression. Moreover, we identified the RAGE-NFκB signalling axis through which the SHP-2 upregulation is conveyed when augmented accumulation of glucose metabolites occur. These findings reveal a basis for potential new therapeutic approaches to prevent accelerated CAD and PAD in diabetic patients since independent pharmacological inhibition of every step in the RAGE-NFκB-SHP-2 axis was sufficient to reset the aberrant monocyte activation.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): Interdisciplinary Center for Clinical Research of the Medical Faculty of the University of Münster