Mitochondrial Dynamics and VMP1-Related Selective Mitophagy in Experimental Acute Pancreatitis

Abstract

Mitophagy and zymophagy are selective autophagy pathways early induced in acute pancreatitis that may explain the mild, auto limited, and more frequent clinical presentation of this disease. Adequate mitochondrial bioenergetics is necessary for cellular restoration mechanisms that are triggered during the mild disease. However, mitochondria and zymogen contents are direct targets of damage in acute pancreatitis. Cellular survival depends on the recovering possibility of mitochondrial function and efficient clearance of damaged mitochondria. This work aimed to analyze mitochondrial dynamics and function during selective autophagy in pancreatic acinar cells during mild experimental pancreatitis in rats. Also, using a cell model under the hyperstimulation of the G-coupled receptor for CCK (CCK-R), we aimed to investigate the mechanisms involved in these processes in the context of zymophagy. We found that during acute pancreatitis, mitochondrial O2 consumption and ATP production significantly decreased early after induction of acute pancreatitis, with a consequent decrease in the ATP/O ratio. Mitochondrial dysfunction was accompanied by changes in mitochondrial dynamics evidenced by optic atrophy 1 (OPA-1) and dynamin-related protein 1 (DRP-1) differential expression and ultrastructural features of mitochondrial fission, mitochondrial elongation, and mitophagy during the acute phase of experimental mild pancreatitis in rats. Mitophagy was also evaluated by confocal assay after transfection with the pMITO-RFP-GFP plasmid that specifically labels autophagic degradation of mitochondria and the expression and redistribution of the ubiquitin ligase Parkin1. Moreover, we report for the first time that vacuole membrane protein-1 (VMP1) is involved and required in the mitophagy process during acute pancreatitis, observable not only by repositioning around specific mitochondrial populations, but also by detection of mitochondria in autophagosomes specifically isolated with anti-VMP1 antibodies as well. Also, VMP1 downregulation avoided mitochondrial degradation confirming that VMP1 expression is required for mitophagy during acute pancreatitis. In conclusion, we identified a novel DRP1-Parkin1-VMP1 selective autophagy pathway, which mediates the selective degradation of damaged mitochondria by mitophagy in acute pancreatitis. The understanding of the molecular mechanisms involved to restore mitochondrial function, such as mitochondrial dynamics and mitophagy, could be relevant in the development of novel therapeutic strategies in acute pancreatitis.

Vacuole Membrane Protein 1 (VMP1) Restricts NLRP3 Inflammasome Activation by Modulating SERCA Activity and Autophagy

“…2C). Interestingly, upregulation of gene expression in this pathway suggest that VMP1 KO cells may be more sensitive to exposed cytoplasmic mtDNA which may be increased in VMP1 KO cells, consistent with previous reports demonstrating that VMP1 mediates the selective degradation of damaged mitochondria by mitophagy [29]. We also observed changes in gene expression in genes associated with calcium signaling, including a downregulation of SERCA and upregulation of other genes associated with calcium signaling in VMP1 KO cells (Fig.…”

“…Typically, with NLRP3 activation, p62 is recruited to damaged mitochondria which are then ubiquitinated through a Parkin-mediated mechanism for degradation, but mitophagy is defective in the absence of VMP1 expression which causes an accumulation of damaged mitochondria [51,52]. Additionally, another mechanism that restricts in ammasome activation involves the interaction between p62 and ASC which targets in ammasome components to autophagosomes for degradation although this response is likely defective in VMP1 KO cells [39].…”

TMEM41B and VMP1 modulate cellular lipid and energy metabolism for facilitating dengue virus infection

“…Of note, the number of active mitochondria was lesser in VMP1 KO cells compared to WT cells despite a significant increase in the overall number of mitochondria (Fig 4A). The observation implied an accumulation of dysfunctional mitochondria in VMP1 KO cells, which is consistent with a recent report, demonstrating that VMP1 is also required to recycle malfunctional mitochondria through mitophagy [40]. In alignment with the lower levels of active mitochondria observed in VMP1 KO cells, we parallelly detected a marked reduction of basal cellular respiration in these KO cells (S4A and S4B Fig) . Since FA treatment failed to rescue DENV infection in VMP1 KO cells, we decided to test whether this was due to impaired beta-oxidation capacity.…”

Puerarin Alleviates LPS-Induced H9C2 Cell Injury by Inducing Mitochondrial Autophagy

“…32,33 Drp1 is often upregulated during mitochondrial fission, whereas MFN1 is downregulated during that process. 34,35 Yang et al 36 found that the squamosamide derivative FLZ could inhibit mitochondrial fission via downregulation of Drp1; Liu et al 37 reported that HMGB1 could inhibit mitochondrial fission in lung cancer cells via mediation of Drp1 and MFN1. Our findings were in line with those previous reports, by suggesting that Puerarin could reverse LPS-induced mitochondrial fission in H9C2 cells by regulating Drp1 and MFN1.…”