Autophagy as a novel therapeutic target in vascular calcification

Abstract

2. Is it all necessary or can some of it be deleted as 'off topic' (examples)?As mentioned above it would be important to follow VSMC calcification rather than a mixture of very different disease entities. I still believe that media sclerosis and arteriosclerosis are very different diseases. Authors' response:We thank the reviewer for highlighting this point. We agree with the reviewer that media sclerosis and arteriosclerosis are very different diseases, although they may share some similar common mechanisms. As described above, we have removed the text in section 3.1, section 4.1 and the entire section 4.4 to focus our manuscript on vascular medial calcification. Is it comprehensive or have they missed citing anything important (examples)?It should be clearly stated that there are mTOR dependent and independent ways of inducing autophagy. The Review would benefit to show differences and overlaps of apoptosis, necrosis, necroptosis and autophagy.Authors' response: We thank the reviewer for consideration of this point. We have stated both the TOR dependent and independent autophagy pathways under section 2-The key regulators of autophagy. Under the same section we have also added text on cell death and autophagic cell death and its crosstalk with apoptosis. As commented by reviewer 2, it is not mTOR in yeast, but TOR. We have revised this term accordingly. The additional text has been added as below (Page 7, line 14-23). Furthermore, autophagy pathway could also be regulated by TOR independent pathways like inositol signalling pathways (Sarkar, et al., 2005), Ca 2+ /calpain pathway (Williams, et al., 2008), cAMP pathway (Williams, et al., 2008) etc. It is also interesting to note that autophagy pathway, which is mainly a cellular degradation pathway is intimately linked to cell death and is different from other programmed cell death mechanisms like apoptosis, necrosis and necroptosis. Autophagy cell death is often seen associated with increased number of autophagosomes inside the cell (Yonekawa & Thorburn, 2013). However, there is a complex crosstalk between autophagy and apoptosis where the calpain-mediated cleavage of Atg5 can trigger cell death by apoptosis (Yousefi, et al., 2006). In this review we have only focused on autophagy as a cytoprotective pathway.Reviewer 2 however selective autophagy can degrade specific substrates like mitochondria (

Vascular Calcification—New Insights into Its Mechanism

“…In turn, induced apoptosis generates oxidative stress, further mitochondrial dysfunction, apoptotic bodies, and MVs [135][136][137][138], events that have been mechanistically linked to DNA damage, ER stress, autophagy or mitophagy, and calcium phosphate deposition. It can also induce osteogenic gene induction and transformation into osteogenic phenotype of VSMCs [139][140][141][142]. Apoptosis is not mutually exclusive, but actually complementary to other pathways introduced in this review that eventually lead to VC.…”

PDK4 promotes vascular calcification by interfering with autophagic activity and metabolic reprogramming

“…Autophagy is commonly regarded as a protective mechanism against vascular calcification 11 , but its activity in this role is controversial. Several studies have suggested an increase in autophagic flux and the formation of autophagic vesicles during the calcification process 11 , whereas other investigators have identified that autophagic flux is defective 4,[12][13][14] . These discrepancies may be caused by differences in cell types, assay conditions, or methods to measure autophagy.…”

“…At pathogenic and clinical levels, vascular calcification shares many similarities with bone formation, and its severity is commonly accompanied by a heightened risk of cardiovascular events and all-cause mortality; however, no therapeutics are currently available. Multiple cardiovascular-related cells, including endothelial cells, pericytes, vascular smooth muscle cells (VSMCs) and valve interstitial cells, are involved in vascular calcification, and among these, VSMCs are the predominant cell type involved, having biosynthetic, proliferative and contractile roles in the vessel wall 3,4 . Continuous intracellular or environmental stimuli, including oxidative stress, hypoxia, abnormal mineral metabolism, apoptosis and chronic inflammation, contribute to a phenotypic change of VSMCs to osteoblast-like cells, in which master transcription factors of osteogenesis and chondrogenesis are upregulated concomitant with the generation of mineralized extracellular matrix; parallel with this process, VSMCs lose a range of contractile proteins, eventually causing vascular calcification 5 .…”

The role of mitochondria in vascular calcification

“…Upregulation of mitophagy might restore mitochondrial function. [67] Highconcentration phosphate could promote the production of mitochondrial superoxide anion and then activate the autophagy of VSMCs. When autophagy was suppressed, the calcium deposition was increased and VSMCs released more MVs and EVs, which contained high ALP activity and accelerated the development of VC.…”

“…[106] In addition, the autophagy process could also maintain the mitochondrial homeostasis to regulate calcification process. [107] With the maturation of gene-editing technology, there were more increasing studies on the root of diseases, so in the future, the regulation of mtDNA stability or even directly affecting POLG might be a potential therapeutic target. Therefore, some measures point to mitochondria might also be a novel insight into VC.…”