Detection of Hsp60 in saliva and serum from type 2 diabetic and non-diabetic control subjects

Abstract

There is increasing evidence that mitochondrial dysfunction and oxidative stress may be integral to the pathogenesis of type 2 diabetes mellitus. Heat shock protein (Hsp60) is a mitochondrial stress protein known to be induced under conditions of mitochondrial impairment. Although this intracellular protein is normally found in the mitochondrion, several studies have shown that this protein is also present in systemic circulation. In this study, we report the presence of elevated levels of Hsp60 in both saliva and serum of type 2 diabetic patients compared to non-diabetic controls. Hsp60 was detectable in the saliva of 10% of control and 93% of type 2 diabetic patients. Levels detected were in the range of 3-7 ng/ml in control and 3-75 ng/ml in type 2 diabetic patients. Serum Hsp60 levels in the range of 3-88 ng/ml were detected in 33% of control subjects, and levels in the range of 28-1,043 ng/ml were detected in 100% of type 2 diabetic patients. This is the first reporting of the presence of mitochondrial stress protein in salivary secretions. The serum Hsp60 levels were 16-fold higher compared to those in saliva, and there was a good positive correlation between salivary and serum Hsp60 levels (r=0.55). While the exact mechanisms responsible for the secretion of Hsp60 into biological fluids such as saliva and blood are not yet known. The presence of this molecular marker of mitochondrial stress in saliva offers a non-invasive route to further investigate the biological functions of extracellular Hsp60 in type 2 diabetes mellitus and other conditions.

Extracellular Heat Shock Proteins

“…In addition, extracellular levels of Hsp70 have been correlated with severity and survival after chronic heart failure (110). Hsp60 has also been detected in saliva and serum of type 2 diabetic patients (111), whereas Hsp70 has been found during diabetic ketoacidosis (112). Both Hsp70 and Hsp60 have been detected in circulation after soft tissue trauma (113).…”

Hyperglycaemia and oxidative stress upregulate HSP60 & HSP70 expression in HeLa cells

“…The primary stressors that elicit this response in T2D are hyperglycaemia and oxidative stress (Mulder and Ling, 2009; Kim et al, 2008; Lowell and Shulman, 2005). T2D has also been found to be associated with elevated levels of heat shock protein 60 (HSP60) (Aguilar-Zavala et al, 2008; Nakhjavani et al, 2010; Yuan et al, 2011). HSPs are a class of ubiquitously expressed and func-tionally related proteins found in all living organisms.…”

“…The induction of one particular HSP, HSP60, has been found to be correlated with mitochondria specific cell stress (Martinus et al, 1996). Recently HSP60 has been found to be secreted and expressed extracellularly, after first being thought to be strictly intracellular where it performs roles as a chaperone and in protein folding (Yuan et al, 2011). However, these mechanisms of translocation and secretion have not been clearly identified.…”

“…It is therefore plausible that the stressors associated with T2D are responsible for the elevated levels of extracellular HSP60 seen in T2D (Nakhjavani et al, 2010; Yuan et al, 2011). To determine if hyperglycaemia and oxidative stress results in the induction of HSP60 expression, HeLa cells were grown in media supplemented with glucose and hydrogen peroxide to simulate hyperglycaemia and oxidative stress respectively.…”

Mycobacterial Hsp65 potentially cross-reacts with autoantibodies of diabetes sera and also induces (in vitro) cytokine responses relevant to diabetes mellitus

“…29 The exact mechanism of secretion of Hsp60 into the biological fluids of T2DM individuals is not yet known.…”