Melatonin is a hormone produced by the pineal gland, and it has extensive beneficial effects on various tissue and organs; however, whether melatonin has any effect on cardiac fibrosis in the pathogenesis of diabetic cardiomyopathy (DCM) is still unknown. Herein, we found that melatonin administration significantly ameliorated cardiac dysfunction and reduced collagen production by inhibiting TGF‐β1/Smads signaling and NLRP3 inflammasome activation, as manifested by downregulating the expression of TGF‐β1, p‐Smad2, p‐Smad3, NLRP3, ASC, cleaved caspase‐1, mature IL‐1β, and IL‐18 in the heart of melatonin‐treated mice with diabetes mellitus (DM). Similar beneficial effects of melatonin were consistently observed in high glucose (HG)‐treated cardiac fibroblasts (CFs). Moreover, we also found that lncRNA MALAT1 (lncR‐MALAT1) was increased along with concomitant decrease in microRNA‐141 (miR‐141) in DM mice and HG‐treated CFs. Furthermore, we established NLRP3 and TGF‐β1 as target genes of miR‐141 and lncR‐MALAT1 as an endogenous sponge or ceRNA to limit the functional availability of miR‐141. Finally, we observed that knockdown of miR‐141 abrogated anti‐fibrosis action of melatonin in HG‐treated CFs. Our findings indicate that melatonin produces an antifibrotic effect via inhibiting lncR‐MALAT1/miR‐141‐mediated NLRP3 inflammasome activation and TGF‐β1/Smads signaling, and it might be considered a potential agent for the treatment of DCM.

Diabetes mellitus (DM) patients are at a higher risk of developing brain injury characterized by neuronal death. Melatonin, a hormone produced by the pineal gland, exerts neuroprotective effects against brain damage. However, the effect of melatonin on diabetes‐induced brain injury has not been elucidated. This study was to evaluate the role of melatonin against neuronal death in DM and to elucidate the underlying mechanisms. Herein, we found that melatonin administration significantly alleviated the neuronal death in both streptozotocin (STZ)‐induced diabetic mice and high glucose (HG)‐treated neuronal cells. Melatonin inhibited neuronal pyroptosis and excessive autophagy, as evidenced by decreased levels of NLRP3, cleaved caspase‐1, GSDMD‐N, IL‐1β, LC3, Beclin1, and ATG12 both in vivo and in vitro. MicroRNA‐214‐3p (miR‐214‐3p) was decreased in DM mice and HG‐treated cells, and such a downregulation was corrected by melatonin, which was accompanied by repression of caspase‐1 and ATG12. Furthermore, downregulation of miR‐214‐3p abrogated the anti‐pyroptotic and anti‐autophagic actions of melatonin in vitro. Our results indicate that melatonin exhibits a neuroprotective effect by inhibiting neuronal pyroptosis and excessive autophagy through modulating the miR‐214‐3p/caspase‐1 and miR‐214‐3p/ATG12 axes, respectively, and it might be a potential agent for the treatment of brain damage in the setting of DM.

Diabetes mellitus (DM) is considered a risk factor for cognitive dysfunction. Harmine not only effectively improves the symptoms of DM but also provides neuroprotective effects in central nervous system diseases. However, whether harmine has an effect on diabetes-induced cognitive dysfunction and the underlying mechanisms remain unknown. In this study, the learning and memory abilities of rats were evaluated by the Morris water maze test. Changes in the nucleotide-binding oligomerization domain-containing protein (NOD)-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome and brain-derived neurotrophic factor (BDNF)/TrkB signaling pathway were determined in both streptozotocin (STZ)-induced diabetic rats and high glucose (HG)-treated SH-SY5Y cells by western blotting and histochemistry. Herein, we found that harmine administration significantly ameliorated learning and memory impairment in diabetic rats. Further study showed that harmine inhibited NLRP3 inflammasome activation, as demonstrated by reduced NLRP3, ASC, cleaved caspase-1, IL-1β, and IL-18 levels, in the cortex of harmine-treated rats with DM. Harmine was observed to have similar beneficial effects in HG-treated neuronal cells. Moreover, we found that harmine treatment enhanced BDNF and phosphorylated TrkB levels in both the cortex of STZ-induced diabetic rats and HG-treated cells. These data indicate that harmine mitigates cognitive impairment by inhibiting NLRP3 inflammasome activation and enhancing the BDNF/TrkB signaling pathway. Thus, our findings suggest that harmine is a potential therapeutic drug for diabetes-induced cognitive dysfunction.

Ferroptosis and ferritinophagy play critical roles in various disease contexts. Herein, we observed that ferroptosis and ferritinophagy were induced both in the brains of mice with diabetes mellitus (DM) and neuronal cells after high glucose (HG) treatment, as evidenced by decreases in GPX4, SLC7A11, and ferritin levels, but increases in NCOA4 levels. Interestingly, melatonin administration ameliorated neuronal damage by inhibiting ferroptosis and ferritinophagy both in vivo and in vitro. At the molecular level, we found that not only the ferroptosis inducer p53 but also the ferritinophagy mediator NCOA4 was the potential target of miR-214-3p, which was downregulated by DM status or HG insult, but was increased after melatonin treatment. However, the inhibitory effects of melatonin on ferroptosis and ferritinophagy were blocked by miR-214-3p downregulation. These findings suggest that melatonin is a potential drug for improving diabetic brain damage by inhibiting p53-mediated ferroptosis and NCOA4-mediated ferritinophagy through regulating miR-214-3p in neurons.

Diabetic cardiomyopathy (DCM) is a serious complication of diabetes mellitus that can cause malignant arrhythmia and sudden death and is associated with cardiomyocyte dysfunction induced by hyperglycemia. Emerging evidence has revealed that transfer RNA-derived fragments (tRFs), a novel class of noncoding RNAs, play a crucial role in a variety of pathophysiologic processes, including cell death, cell growth and proliferation. However, it remains unknown whether and how tRFs are involved in cardiomyocyte dysfunction during the progression of DCM. In this study, we found that cardiomyocyte abnormalities were induced by high glucose (HG) treatment, as demonstrated by a decrease in cell viability and autophagy activation as well as an increase in cell death and proinflammatory cytokine release. Moreover, HG treatment resulted in differential expression of tRFs in cardiomyocytes, of which 4 upregulated and 1 downregulated tRFs were observed compared with the control group. The differential expression of 4 upregulated tRFs was primarily involved in cardiac dysfunction-related processes, such as autophagy, AGE-RAGE signaling pathway in diabetic complications, MAPK signaling pathway, insulin signaling pathway, FoxO signaling pathway, insulin resistance and peroxisome pathways based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Furthermore, we found that tRF-5014a, the most significantly upregulated tRF among all tested tRFs, negatively regulated the expression of the autophagy-related protein ATG5. Importantly, inhibition of tRF-5014a not only abolished autophagy inactivation but also attenuated the decrease in cell viability and increase in cell death as well as proinflammatory cytokine release under HG conditions. These findings suggest that tRFs may contribute to HG-induced cardiomyocyte injury during DCM progression.