Identify proinsulin regulators using CRISPR screen and mouse genetics [CRISPR screen]
Proinsulin is the precursor of insulin in pancreatic beta cells. Altered proinsulin and proinsulin to insulin ratio mark beta cell dysfunction, predictuing disease progression into type 1 and type 2 diabetes. Of essential role for beta cell function, knowledge about proinsulin production and its role in disease are currently very limited. Using genome wide CRISPR screen, we identified 84 proinsulin regulators including classical protein convertases Pcsk1 and Cpe, and novel factors like Pdia6. Among the list 29 proinsulin regulators were trajectory genes involved in disease progression in obesity and type 2 diabetes in humans. In vivo mouse genetics study revealed unique genetic architecture and quantitative trait loci (QTLs) modulating plasma proinsulin levels. Integrative analyzing and mapping of the QTL signals directly pinpointed to proinsulin regulators identified from the CRISPR screen, which in return greatly improved resolution of the mouse genetic study. 4 out of 5 overlapped genes can be individually validated. Knocking down the leading hits Pdia6 leads to decreased proinsulin content and remarkable loss of proinsulin granules in beta cells. Consequently, proinsulin secretion was greatly decreased. Mechanistically, protein translation rate was greatly impaired after knocking down Pdia6. Our study demonstrated the power of combining in vitro functional genomics with in vivo mouse genetics study to identify proinsulin regulatory network in pancreatic beta cells. Overall design: MIN6 cells transfected with the GeCKOv2 library were stained with proinsulin and insulin antibodies. Cells were assigned and sorted into "proinsulin high" and "proinsulin low" populations. Genomic DNA of each cell population were extracted using the Dneasy Blood & Tissue kit (Qiagen) and the sgRNA regions were PCR amplified by Herculase II (Agilent) polymerase using indicated primers. The PCR products were purified with Aline PCR Clean DX magnetic beads and processed into Truseq libraries followed by NGS analysis.