Hydrogen sulfide-modified extracellular vesicles from mesenchymal stem cells for treatment of hypoxic-ischemic brain injury

We previously reported that preconditioning of mesenchymal stem cells (MSCs) with hydrogen sulfide (H2S) improved their therapeutic potential in cerebral ischemia. However, the mechanisms involved with this effect have not been determined. As one approach to address this issue, we focused on a neuroprotective role of modification of MSCs-derived extracellular vesicles (EVs) with H2S treatment, and further examined the underlying mechanisms during hypoxia-ischemia (HI) injury in neonatal mice. At 24 h following HI insult, neonatal mice received either systemically administered EVs (derived from MSCs) or H2S-EVs (derived from NaHS-pre-conditioned MSCs). Both treatments reached the injured region of the ipsilateral hemisphere within 2 h after administration and were incorporated into microglia and neurons. Mice receiving H2S-EVs exhibited substantially lower amounts of brain tissue loss, decreased levels of pro-inflammatory mediators, and a skewed distribution of CD45(low) microglia and CD45(high) brain mononuclear phagocytes toward a more anti-inflammatory condition as compared with that in mice receiving only EVs. Moreover, these neuroprotective and anti-inflammatory effects of H2S-EVs were accompanied with long-term preservation of cognitive and memory functions, in contrast to the functional deficits observed in mice receiving only EVs. This H2S preconditioning upregulated miR-7b-5p levels in EVs as determined with next-generation sequencing, while knockdown analyses revealed that inducing miR-7b-5p expression and targeting FOS in the ipsilateral cortex were essential for the neuroprotective and anti-inflammatory effects of H2S-EVs following HI exposure. Taken together, these results demonstrate that miR-7b-5p transferred by H2S-EVs into the ipsilateral hemisphere further induced miR-7b-5p expression, which promoted CD45(low) microglia and CD45(high) brain mononuclear phagocytes toward a beneficial phenotype and improved HI-induced cognitive impairments in neonatal mice.