Introduction
Gene therapy holds great promise for the treatment of various diseases. AAVpan mediated SPINK1 overexpression has shown considerable promise in alleviating pancreatitis [1]. However, in the case of severe pancreatitis induced by high-dose caerulein administration, the protective effect was not markedly evident possibly due to the insufficient expression of SPINK1. To ensure therapeutic levels of hSPINK1 expression within the safe dosage range of AAV, we introduced the short intron 1 (mini intron1) sequence of hSPINK1 gene to explore whether mini-intron could enhance hSPINK1 expression, and validated the therapeutic efficacy of the AAVpan-hSPINK1-mini intron1 in pancreatitis models.
Aims & Methods
The first intron of human SPINK1 (1.8 kb) conforms to significantly enhance gene expression [2]. Considering limited packaging capacity of AAV (4.7 kb), we introduce the first and last 50 base pairs (which do not affect splicing) into hSPINK1 cDNA to construct hSPINK1-mini intron1. First, we investigated whether mini intron could enhance hSPINK1 overexpression: the hSPINK1 expression levels in AAVpan-hSPINK1 and AAVpan-hSPINK1-mini intron1 group were compared using qRT-PCR, Western blot, and trypsin-inhibition assays. The stability of hSPINK1 mRNA in both groups were evaluated following in vitro transcriptional inhibition with actinomycin D. Then, we evaluated the safety of mini intron-mediated hSPINK1 overexpression by detecting hepatic and renal function as well as pancreatic histology. Further, we constructed cerulein-induced severe acute pancreatitis model (250 μg/kg/h) to determine the protective effectiveness of mini intron-mediated overexpression.
Results
The AAVpan-hSPINK1-mini intron1 demonstrated substantially enhanced hSPINK1 expression compared to the AAVpan-hSPINK1. Quantitative analysis revealed a remarkable 30-fold increase in hSPINK1 mRNA levels, 7-fold elevation in protein expression, and 1.5-fold improvement in trypsin-inhibition activity in the AAVpan-hSPINK1-mini intron1 group than those in AAVpan-hSPINK1 group. The addition of actinomycin D resulted in continuous decay of hSPINK1 mRNA in AAVpan-hSPINK1 group, whereas the hSPINK1 mRNA levels in AAVpan-hSPINK1-mini intron1 group remained stable, indicating that mini intron1 effectively stabilized hSPINK1 mRNA. In safety analysis, the histological analysis of liver and pancreas, hepatic and renal function, as well as serum amylase remained within normal levels in both groups for up to 8 weeks post-injection. In the AAVpan-hSPINK1 group, mice with high-dose caerulein-induced SAP exhibited typical pancreatitis phenotypes. In contrast, the AAVpan-hSPINK1-mini intron1 attenuated SAP, implying a dose-dependently protective effect of hSPINK1 overexpression.
Conclusion
The enhanced mini intron could safely enhanced hSPINK1 expression level and trypsin-inhibition activity by improving mRNA stability, representing a promising strategy for optimizing transgene expression and opening up new possibilities for the treatment of severe pancreatitis and potentially other diseases in the field of gene therapy.
References
[1] Wang YC, Mao XT, Sun C, et al. Pancreas-directed AAV8-hSPINK1 gene therapy safely and effectively protects against pancreatitis in mice [J]. Gut, 2024, 73(7): 1142-55.
[2] Kereszturi E, Király O, Sahin-Tóth M. Minigene analysis of intronic variants in common SPINK1 haplotypes associated with chronic pancreatitis [J]. Gut, 2009, 58(4):545-9.