粒線體鈣離子湧入導致之活性氧類釋放活化細胞自噬

Abstract

細胞自噬為細胞吞食自身組成物的機制，其目的在於維持細胞正常功能與健康。細胞飢餓時，細胞自噬體主要形成於內質網與粒線體交界處。目前研究仍不清楚細胞如何即時在該處激發自噬體生成。因此，本篇研究著重於探討內質網與粒線體的鈣離子、活性氧類訊息傳導路徑如何在此處調控細胞自噬體生成。我們使用共軛焦顯微鏡觀察活細胞之細胞自噬活性，並在處理鈣離子、活性氧類抑制物後偵測細胞自噬活性的改變。我們發現細胞自噬活性在飢餓10-15分鐘時有顯著增加。另外，細胞自噬激發發生前，我們觀察到鈣離子湧入粒線體、粒線體活性氧類製造與釋放增加，而抑制這些現象導致細胞自噬激發消失。我們實驗室先前研究中發現同時期之 LC3去連結酶Atg4活性受抑制。此外，我們看到細胞膜損壞所引起之細胞自噬受粒線體活性氧類釋放調控。綜合以上結果，我們提出以下模式：短期飢餓時，鈣離子進入粒線體，引發粒線體製造並釋出活性氧類。釋出之活性氧類透過抑制該處Atg4以活化細胞自噬。此鈣離子活性氧類調控路徑為一普遍細胞自噬控制機制。此路徑不僅參與飢餓與細胞膜損壞引起的細胞自噬，也可能影響其他跟鈣離子擾動相關的細胞自噬活化。

Autophagy, a self-digestive mechanism, is vital for cellular functions and health. During starvation, autophagosomes form mainly at the endoplasmic reticulum (ER)-mitochondria contact sites. However, how cells timely induce autophagy at these sites are unclear. We aimed to elucidate the roles of ER and mitochondrial calcium-reactive oxygen species (ROS) signaling in autophagosome formation at these sites. We used confocal live-cell imaging to monitor autophagy activity in the absence or presence of calcium and ROS inhibitors. We found that autophagy activity burst at 10-15 minutes of starvation. The autophagy burst was preceded by mitochondrial calcium influx, mitochondrial ROS production and release; the inhibition of these phenomena abolished autophagy burst. Previously, our lab saw Atg4, an LC3 de-conjugating enzyme, was inhibited in the same time frame. Additionally, autophagy induced by plasma membrane damage was also controlled by mitochondrial ROS release. Taken together, we propose that during short-term starvation, mitochondrial calcium influx induces ROS production and release. ROS then facilitate autophagy by local Atg4 inhibition. This calcium-ROS signaling pathway may represent a general autophagy regulatory mechanism in starvation, plasma membrane damage and other autophagy stimuli that involve calcium perturbations.