Pregnancy-associated plasma protein-aa supports hair cell survival by regulating mitochondrial function

Abstract

To support cell survival, mitochondria must balance energy production with oxidative stress. Inner ear hair cells are particularly vulnerable to oxidative stress; thus require tight mitochondrial regulation. We identified a novel molecular regulator of the hair cells’ mitochondria and survival: Pregnancy-associated plasma protein-aa (Pappaa). Hair cells in zebrafish pappaa mutants exhibit mitochondrial defects, including elevated mitochondrial calcium, transmembrane potential, and reactive oxygen species (ROS) production and reduced antioxidant expression. In pappaa mutants, hair cell death is enhanced by stimulation of mitochondrial calcium or ROS production and suppressed by a mitochondrial ROS scavenger. As a secreted metalloprotease, Pappaa stimulates extracellular insulin-like growth factor 1 (IGF1) bioavailability. We found that the pappaa mutants’ enhanced hair cell loss can be suppressed by stimulation of IGF1 availability and that Pappaa-IGF1 signaling acts post-developmentally to support hair cell survival. These results reveal Pappaa as an extracellular regulator of hair cell survival and essential mitochondrial function.

The metalloproteinase Papp-aa controls epithelial cell quiescence-proliferation transition

“…Currently, there are no antibodies available against these zebrafish IGF ligands, making it 369 impossible to measure IGF release after NBI-31772 treatment. To circumvent this problem, we 370 treated zebrafish embryos with free IGF1 following a recent paper(Alassaf et al, 2019).371 Addition of either human or fish IGF-1 increased NaR cell proliferation, supporting the idea that 372 bioavailability of IGFs is critical. 373 IGFBP5/Igfbp5a has been shown to both inhibit and potentiate IGF actions in 374 mammalian and zebrafish cells in vitro and in vivo (Zheng et al, 1998; Zheng et al, 1998; Ren 375 et al, 2008; Dai et al, 2010; Liu et al, 2018; Duan & Allard, 2020).…”

“…The samples were collected for 583 immunostaining after 24 hours of treatment or for in situ hybridization after 48 hours of 584 treatment. The IGF1 treatment experiment was carried out as reported by Alassaf et al (2019). 585 Tg(igfbp5a:GFP) fish were treated with recombinant fish (salmon) and human IGF-1 at 150 586 ng/ml (GroPrep, dissolved in 10 µM HCl and diluted in E3 embtyo medium) from 3 dpf to 5 dpf.…”

Pregnancy associated plasma protein-aa regulates endoplasmic reticulum-mitochondria associations

“…For neurons with high 50 metabolic demands, such as sensory hair cells, precise regulation of ER-mitochondria 51 associations is especially critical for cell survival. We previously identified the secreted 52 metalloprotease Pregnancy associated plasma protein-aa (Pappaa) as a novel regulator of 53 mitochondrial function in zebrafish lateral line hair cells (Alassaf et al, 2019). Here, we show 54 that pappaa mutant hair cells exhibit excessive and abnormally close ER-mitochondria 55 associations, suggesting increased ER-mitochondria calcium transfer.…”

“…Each neuromast consists of a cluster of hair cells 132 surrounded by the glia-like support cells. Our previous work showed that hair cells in pappaa 133 mutants (hereafter referred to as pappaa p170 ) are more susceptible to ROS-induced death and 134 their mitochondria have increased calcium load (Alassaf et al, 2019). Therefore, we 135 hypothesized that pappaa p170 mitochondria may have an increased frequency of ER-136 mitochondria associations.…”

The metalloproteinase Papp-aa functions as a molecular switch linking IGF signaling to adaptive epithelial growth

“…Zebrafish has three genes belonging to the pappalysin family, papp-aa, papp-ab, andpapp-a2 (Kjaer-Sorensen et al, 2013, 2014;Wolman et al, 2015). To date, published whole mount in situ hybridization data showed that papp-aa mRNA is expressed in various neural tissues, papp-ab mRNA in developing myotomes and brain (Kjaer-Sorensen et al, 2013;Wolman et al, 2015;Miller et al, 2018;Alassaf et al, 2019), and papp-a2 in the notochord and brain (Kjaer-Sorensen et al, 2014). Because NaR cells are located on the yolk sac skin, they are more sensitive to permeabilization by protease K treatment, a key step in the whole mount in situ hybridization procedure.…”