The role of SLMAP as therapeutic targets

Arun Lakshmanan1, Balwant Tuana2, Hong Ding1. 1WCMC-Q, Doha, Qatar, 2University of Ottawa, Ottawa, Canada.

Sarcolemmal membrane associated proteins (SLMAP) belongs to the superfamily of tail-anchored membrane proteins and is highly expressed in the endoplasmic reticulum (ER)/sarcoplasmic reticulum (SR) as well as the mitochondria, cell surface membranes and the nuclear envelope. It has been reported to be involved in ion channel regulation, membrane fusion and vesicle transport. Previously, our group demonstrated that SLMAP is upregulated in diabetic db/db mice and Tally Ho mice, and involves in regulation of glucose transporters and cardiac SR/ER function1,2. Although the exact role of SLMAP remains subtle, we hypothesize that upregulated SLMAP contributes to hyperglycaemia-induced ER stress and apoptosis, and aim to elucidate the potential role of SLMAP in diabetes and possible mechanisms that might offer potential targets to treat diabetes.

The overexpression of SLMAP in HEK293 cell line was achieved by using SLMAP expression constructs or SLMAP lentiviral particles. The HEK293 cells were maintained in either normal glucose (NG, 5.5mM) or high glucose (HG, 33mM) media for 48 or 72 hrs. Statistical analysis of the data was performed using Student’s t test (GraphPad Prism 5.0). P<0.05 was used to indicate statistical significance.

The overexpression of SLMAP in HEK293 cells significantly decreased the phosphorylation of AMP-activated protein kinase alpha (AMPKα) when comparing to negative control (-ve ctrl) in both normal and high glucose media (1.132±0.10 vs 0.604±0.11, p<0.01, NG+-ve ctrl vs NG+ SLMAP & 0.793±0.07 vs 0.568±0.06, p<0.05, HG+-ve ctrl vs HG+SLMAP). The overexpression of SLMAP also significantly increased the expression of ER stress chaperone protein-GRP78 (0.750±0.01 vs 0.907±0.01, p<0.01, NG+-ve ctrl vs NG+ SLMAP & 0.733±0.01± 0.998±0.06, p<0.01, HG+-ve ctrl vs HG+SLMAP). Moreover, oxidative stress was increased in SLMAP overexpressed HEK293 cells evaluated by DHE fluorescent staining comparing to control (P<0.05). In addition, overexpression of SLMAP in HEK293 cells significantly decreased anti-apoptotic marker protein-BCL-xL (p<0.05, NG+-ve ctrl vs NG+ SLMAP and HG+-ve ctrl vs HG+SLMAP); and interestingly it promoted the expression of pro-apoptotic marker protein-caspase 3 only in HG condition (p<0.05), not in NG condition (P>0.05).

In conclusion, SLMAP plays important roles in hyperglycaemia -induced ER / oxidative stress and promotes apoptosis, possibly via an AMPK-dependent signalling pathway and might offer novel therapeutic targets for the treatment of type 2 diabetes.

(1) Ding et al (2005) AJP 289(1):H206-211.

(2) Chen & Ding (2011) Exp Diabetes Res. 421982.

This work was supported by a National Priorities Research Program grant (NPRP 5-149-3-040).