Total RNA of each lung sample was extracted by using TRIzol Reagent (Invitrogen, US) and further purified using the RNeasy Mini Kit (Qiagen, Germany) according to the manufacturer's instructions. Total RNA of each sample was quantified and qualified by Agilent 2100 Bioanalyzer (Agilent Technologies, USA), NanoDrop (Thermo Fisher Scientific Inc., USA) and 1% agarose gel. Total RNA (1 μg) with the value of RNA integrity number (RIN) > 7 was used for library preparation of the following next generation sequencing, with the NEBNext Ultra II Directional RNA Library Prep. Kit for Illumina. The rRNA was depleted from total RNA using Ribo-Zero™ rRNA removal Kit (Illumina, USA), and cDNA libraries were generated following manufacture's protocols. Libraries with different indices were multiplexed and loaded on Illumina HiSeq instrument (Illumina, USA) for 2 × 150 paired-end sequencing according to manufacturer's instructions.