Jiabing Fan^1,2,†, Chung-Sung Lee^1,†, Soyon Kim¹, Chen Chen¹, Tara Aghaloo³, Min Lee^1,2,4,*

¹Division of Advanced Prosthodontics, School of Dentistry, University of California, Los Angeles, California, 90095, USA.
²Weintraub Center for Reconstructive Biotechnology, School of Dentistry, University of California, Los Angeles, California, 90095, USA.
³Division of Diagnostic and Surgical Sciences, School of Dentistry, University of California, Los Angeles, California, 90095, USA.
⁴Department of Bioengineering, University of California, Los Angeles, California, 90095, USA.

^†These authors contributed equally to this work
^*To whom correspondence should be addressed:

Administration of exosomes is considered an attractive cell-free approach to skeletal repair and pathological disease treatment. However, poor yield for the production technique and unexpected therapeutic efficacy of exosomes have been obstacles to their widespread use in clinical practices. Here, we report an alternative strategy to produce exosome-related vesicles with high yields and improved regenerative capability. An extrusion approach was employed to amass exosome mimetics (EMs) from human mesenchymal stem cells (hMSCs). The collected EMs had a significantly increased proportion of vesicles positive for the exosome-specific CD-63 marker compared with MSC-derived exosomes. EMs were further obtained from genetically modified hMSCs in which expression of noggin, a natural bone morphogenetic protein antagonist, was down-regulated to enhance osteogenic properties of EMs. Moreover, the administration of hMSC-EMs in conjunction with an injectable chitosan hydrogel into mouse nonhealing calvarial defects demonstrated robust bone regeneration. Importantly, mechanistic studies revealed that the enhanced osteogenesis by EMs in which noggin was suppressed was mediated via inhibition of miR-29a. These findings demonstrate the great promise of MSC-mediated EMs and modulation of small RNA signaling for skeletal regeneration and cell-free therapy.

KEYWORDS: exosome mimetics, MSCs, noggin suppression, sRNAs, bone