Objectives Bone marrow mesenchymal stem cells (BM-MSCs) have been employed as a therapeutic means, to cure multiple ischaemic injuries, including acute myocardial infarction (AMI). However, the anaemic condition inside the infarcted area provides an obstacle for survival. Hypoxia preconditioning can reduce apoptosis of BM-MSCs. This study explored the impact of a hypoxia related up-regulation of leptin in BM-MSC on anti-apoptosis.

Methods Human bone marrow mononuclear cells (BMNCs) were isolated using Ficoll 400. BM-MSCs are separated by adhering to the flask bottom. BM-MSCs were characterised by detecting cell surface antigens using flow cytometry. BM-MSCs were tested from passage 3∼8 incubated under 0.5% O₂, 37°C for 24 h, and prolonged with a 2-h re-oxygen. BM-MSCs cultured in normoxia condition were employed as the control group. Both cells were exposed to an oxygen, glucose and serum deprived (OGSD) condition for 36 h. Endogenous expression of leptin was tested using western blot and ELISA. Leptin neutralising antibody and signalling pathway inhibitors were used. Apoptosis was detected by nuclear staining using DAPI and TUNEL assay. The possible mechanism was assessed using flow cytometry of Annexin V/PI and PI/RNase. Associated signalling pathways were assayed by western blot. Fatal mice cardiac myocytes were isolated and seeded for co-culture in a apoptosis model, with either conditioned medium (CM) from BM-MSCs or BM-MSCs. Fatal mice cardiac myocytes viability was screened by TUNEL assay.

Results Endogenous expression of leptin was up-regulated in hypoxic pre-conditioned BM-MSCs. Leptin improves anti-apoptosis ability, since it was abolished by leptin neutralising antibody. The anti-apoptosis ability was introduced by activating PI3K/Akt, Erk1/2, and JAK2/STAT3 pathways, respectively. Fatal mice cardiac myocytes co-cultured with CM but not BM-MSC, gained better survival rate vs control group.

Conclusions Hypoxia related up-regulation of endogenous leptin improves the anti-apoptosis ability of BM-MSCs through multiple survival associated signalling pathways. This BM-MSC protects fatal mice cardiac myocytes from apoptosis via Bcl-2/Bax pathway.