A Sensitive Reporter Mouse Model to Study Adipocyte-Derived Extracellular Vesicles In Vivo.

Extracellular vesicles (EVs) affect the function of cells in living animals. Yet, cell type-specific EV abundances and their distribution in biological fluids are technically challenging to study. Thus, we aimed to develop an in vivo EV reporter system to monitor cell-type-specific EVs, with a focus on adipocyte-derived EVs. While our previously generated EV reporter construct had insufficient sensitivity, we successfully created a sensitive EV reporter using an adeno-associated virus (AAV) vector with Cre-activated expression of human CD63 fused to NanoLuc (CD63-NanoLuc). Moreover, we designed a control AAV construct for monitoring constitutive secretion of NanoLuc (sec-NanoLuc). AAV administration to mice induced adipocyte-specific expression of both reporters. NanoLuc activity was detected in plasma. While sec-NanoLuc was predominantly in plasma and urine, CD63-NanoLuc was highest in adipose tissues (ATs). We challenged mice with a 2-week high-fat diet (HFD), which had minimal effects on body weight and adipogenic markers. Still, the HFD-fed CD63-NanoLuc mice, but not sec-NanoLuc mice, showed significantly higher NanoLuc activity in ATs, lungs, kidneys and urine. Thus, our CD63-NanoLuc and sec-NanoLuc constructs revealed an early effect of HFD on the abundance and distribution of adipocyte-derived EVs and provide a sensitive system for monitoring cell-type-specific EVs in health and disease.