Characterisation of key enzymes required for the glycosylation and efficient secretion of HMW adiponectin — ASN Events
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  3. Characterisation of key enzymes required for the glycosylation and efficient secretion of HMW adiponectin

Characterisation of key enzymes required for the glycosylation and efficient secretion of HMW adiponectin (#143)

Julie Webster 1 2 , Yu-Hee Kim 1 2 3 , Choa Ping Ng 1 , Jon Whitehead 1 2
  1. MMRI, South Brisbane, QLD, Australia
  2. University of Queensland, Brisbane, QLD, Australia
  3. Diamantina Institute, Brisbane, QLD, Australia

Adiponectin is an adipocyte secreted hormone with salutary metabolic, anti-inflammatory and anti-atherogenic properties. It circulates as low molecular weight(LMW) and high molecular weight(HMW) multimers.  Paradoxically, given adiponectin is secreted from adipocytes, circulating levels decrease with obesity.  This reflects a specific loss of the metabolically active HMW species.  Formation and efficient secretion of HMW adiponectin is dependent on post-translational modifications(PTMs), including PTM of conserved lysines in the collagenous domain.  These lysines are modified by hydroxylation and glycosylated by galactose and glucose.  The enzymes responsible for these PTMs have not been defined. 

The aim of this work was to characterize the enzymes responsible for the PTMs, define their functional significance in the context of adiponectin multimerisation, and investigate a putative role in the pathophysiology of hypoadiponectinaemia.  Candidates were identified based on their activities towards collagen.  Lysyl hydroxylase 3(LH3) is a multifunctional enzyme that has hydroxylase activity, limited galactosyltransferase activity and glucosyltransferase activity.  Glycosyl transferase 25 Domain 1(GLT25D1) was recently identified and shown to have high galactosyltransferase activity. 

siRNA mediated knockdown of LH3 and GLT25D1 was used to investigate the role of the enzymes on adiponectin multimerisation and secretion.  Preliminary studies in human SGBS preadipocytes revealed a requirement for both enzymes in adipogenesis. Differentiation was compromised upon knockdown of LH3 or GLT25D1.  Subsequent studies were performed in HEK cells stably expressing human adiponectin.  Knockdown of LH3 decreased the secretion of both total and HMW adiponectin whereas knockdown of GLT25D1 decreased secretion of HMW, but not total.  mRNA levels of both enzymes in adipose tissue from lean and obese mice were not significantly decreased.

These results demonstrate that LH3 and GLT25D1 activity are required for efficient secretion and/or multimerisation of adiponectin as well as adipogenesis.  However, decreased mRNA expression of LH3 and GLT25D1 does not appear to contribute to obesity related hypoadiponectinaemia.