The impact of NRG1 expressions and methylation on multifactorial Hirschsprung disease

Neuregulin 1 (NRG1) and its receptors in the enteric nervous system and other parts of the gastrointestinal wall

Neuregulin 1 (NRG1) belonging to the transmembrane growth factors family is widespread in living organisms. It acts through ErbB family receptors and first of all takes part in embryogenesis, as well as in developmental, regenerative and adaptive processes occurring in various internal organs and systems. It is known that NRG1 and its receptors are present in various parts of the gastrointestinal (GI) tract. First of all NRG1 and ErbB receptors have been detected in the enteric nervous system (ENS) localized in the wall of the esophagus, stomach and intestine and regulating the majority of the GI tract functions, but also in the mucosal and muscular layers of the GI tract. The NRG1/ErbB pathway is involved in the development and differentiation of the ENS and regulation of the intestinal epithelium functions. Moreover, dysregulation of this pathway results in a wide range of gastrointestinal diseases. However, till now there are no summarizations of previous studies concerning distribution and functions of NRG1 and its receptors in the GI tract. The present review fills this gap.

Aberrant SOX10 and RET expressions in patients with Hirschsprung disease

BACKGROUND

HSCR is a complex genetic disorder characterized by the absence of ganglion cells in the intestine, leading to a functional obstruction. It is due to a disruption of complex signaling pathways within the gene regulatory network (GRN) during the development of the enteric nervous system (ENS), including SRY-Box Transcription Factor 10 (SOX10) and REarranged during Transfection (RET). This study evaluated the expressions of SOX10 and RET in HSCR patients in Indonesia.

METHODS

Total RNA of 19 HSCR ganglionic and aganglionic colons and 16 control colons were analyzed using quantitative real-time polymerase chain reaction for SOX10 and RET with GAPDH as the reference gene. Livak's method (2-ΔΔCT) was used to determine the expression levels of SOX10 and RET.

RESULTS

Most patients were males (68.4%), in the short aganglionosis segment (78.9%), and had undergone transanal endorectal pull-through (36.6%). There were significant upregulated SOX10 expressions in both ganglionic (2.84-fold) and aganglionic (3.72-fold) colon of HSCR patients compared to controls' colon (ΔCT 5.21 ± 2.04 vs. 6.71 ± 1.90; p = 0.032; and ΔCT 4.82 ± 1.59 vs. 6.71 ± 1.90; p = 0.003; respectively). Interestingly, the RET expressions were significantly downregulated in both ganglionic (11.71-fold) and aganglionic (29.96-fold) colon of HSCR patients compared to controls' colon (ΔCT 12.54 ± 2.21 vs. 8.99 ± 3.13; p = 0.0004; and ΔCT 13.90 ± 2.64 vs. 8.99 ± 3.13; p = 0.0001; respectively).

CONCLUSIONS

Our study shows aberrant SOX10 and RET expressions in HSCR patients, implying the critical role of SOX10 and RET in the pathogenesis of HSCR, particularly in the Indonesian population. Our study further confirms the involvement of SOX10-RET within the GNR during the ENS development.

The interplay of common genetic variants NRG1 rs2439302 and RET rs2435357 increases the risk of developing Hirschsprung's disease

Introduction: As a congenital and genetically related disease, many single nucleotide polymorphisms (SNPs) have been reported to be associated with the risk of HSCR. Our previous research showed that SNP rs2439302 (NRG1) interacted with rs2435357 (RET) to increase the risk of HSCR development. However, the underlying molecular mechanism is still not well understood. Methods: SNP rs2439302 (NRG1) and rs2435357 (RET) were genotyped in 470 HSCR cases. The expression of NRG1 and RET was investigated in the colon of HSCR patients. Knockdown of the NRG1 and RET homologs was performed in zebrafish to investigate their synergistic effect on ENS development. The effect of SNP rs2439302 and rs2435357 polymorphism on neuron proliferation, migration, and differentiation were investigated in SHSY-5Y cells and IPSCs. Results: Significant downregulation of NRG1 and RET expression was noticed in the aganglionic segment of HSCR patients and SHSY-5Y cells with rs2439302 GG/rs2435357 TT genotype. NRG1 and RET double mutants caused the most severe reduction in enteric neuron numbers than NRG1 single mutant or RET single mutant in the hindgut of zebrafish. SHSY-5Y cells and IPSCs with rs2439302 GG/rs2435357 TT genotype exhibited a decreased proliferative, migration, and differentiative capacity. CTCF showed a considerably higher binding ability to SNP rs2439302 CC than GG. NRG1 reduction caused a further decrease in SOX10 expression via the PI3K/Akt pathway, which regulates RET expression by directly binding to rs2435357. Discussion: SNP rs2439302 (NRG1) GG increases the risk of developing HSCR by affecting the binding of transcription factor CTCF and interacting with rs2435357 (RET) to regulate RET expression via the PI3K/Akt/SOX10 pathway.