NNMT Inhibitor(UT Health Science Center at San Antonio)

We aim to explore the potential of nicotinamide n-methyltransferase (NNMT) as a sensitive marker of renal tubular injury and the possibility of an NNMT inhibitor to combine with sodium-glucose cotransporter 2 (SGLT2) inhibitor to protect proximal tubular epithelium in vivo and in vitro model of Type 2 diabetes mellitus (T2DM), respectively.

In vivo, immunohistochemical staining, Masson's trichrome staining and Sirius red staining were used to observe the changes of NNMT expression, renal tubular injury and interstitial fibrosis in renal tissue from the db/db mice. Bioinformatic analysis was also conducted to broaden the range of data validation. In vitro, Western Blot and quantitative RT-PCR were used to measure the degree of damage of HK-2 cells.

Our in vivo data showed upregulation of NNMT expression paralleled renal tubular damage and interstitial fibrosis. Our in vitro data revealed both NNMT inhibitors and SGLT2 inhibitors can protect against the injury as assessed by extracellular matrix (ECM) synthesis and profibrotic phenotype transition of HK-2 cells, and the combination of these two agents can further reduce these injuries.

The present study is the first to show that NNMT is a promising marker of renal tubular injury in diabetic nephropathy (DN) and NNMT inhibitors can synergize with SGLT2 inhibitors to protect HK-2 better. Our findings will provide the insight and pave the way of developing novel therapeutic strategies for chronic renal tubular injury associated with T2DM.

Development of resistance to platinum (Pt) in ovarian cancer remains a major clinical challenge. Here we focused on identifying epitranscriptomic modifications linked to Pt resistance. Fat mass and obesity-associated protein (FTO) is a N6-methyladenosine (m6A) RNA demethylase that we recently described as a tumor suppressor in ovarian cancer. We hypothesized that FTO-induced removal of m6A marks regulates the cellular response of ovarian cancer cells to Pt and is linked to the development of resistance. To study the involvement of FTO in the cellular response to Pt, we used ovarian cancer cells in which FTO was knocked down via short hairpin RNA or overexpressed and Pt-resistant (Pt-R) models derived through repeated cycles of exposure to Pt. We found that FTO was significantly downregulated in Pt-R versus sensitive ovarian cancer cells. Forced expression of FTO, but not of mutant FTO, increased sensitivity to Pt in vitro and in vivo (P < 0.05). Increased numbers of γ-H2AX foci, measuring DNA double-strand breaks, and increased apoptosis were observed after exposure to Pt in FTO-overexpressing versus control cells. Through integrated RNA sequencing and MeRIP sequencing, we identified and validated the enzyme nicotinamide N-methyltransferase (NNMT), as a new FTO target linked to Pt response. NNMT was upregulated and demethylated in FTO-overexpressing cells. Treatment with an NNMT inhibitor or NNMT knockdown restored sensitivity to Pt in FTO-overexpressing cells. Our results support a new function for FTO-dependent m6A RNA modifications in regulating the response to Pt through NNMT, a newly identified RNA methylated gene target.