Chondroitin sulfate proteoglycans negatively regulate the positioning of mitochondria and endoplasmic reticulum to distal axons

Abstract

Chondroitin sulfate proteoglycans (CSPGs) are components of the extracellular matrix that inhibit the extension and regeneration of axons. However, the underlying mechanism of action remains poorly understood. Mitochondria and endoplasmic reticulum (ER) are functionally inter-linked organelles important to axon development and maintenance. We report that CSPGs impair the targeting of mitochondria and ER to the growth cones of chicken embryonic sensory axons. The effect of CSPGs on the targeting of mitochondria is blocked by inhibition of the LAR receptor for CSPGs. The regulation of the targeting of mitochondria and ER to the growth cone by CSPGs is due to attenuation of PI3K signaling, which is known to be downstream of LAR receptor activation. Dynactin is a required component of the dynein motor complex that drives the normally occurring retrograde evacuation of mitochondria from growth cones. CSPGs elevate the levels of p150Glu dynactin found in distal axons, and inhibition of the interaction of dynactin with dynein increased axon lengths on CSPGs. CSPGs also decreased the membrane potential of mitochondria, and pharmacological inhibition of mitochondria respiration at the growth cone independent of manipulation of mitochondria positioning impaired axon extension. Combined inhibition of dynactin and potentiation of mitochondria respiration further increased axon lengths on CSPGs relative to inhibition of dynactin alone. These data reveal that the regulation of the localization of mitochondria and ER to growth cones is a previously unappreciated aspect of the effects of CSPGs on embryonic axons.

Deacetylation of Miro1 by HDAC6 blocks mitochondrial transport and mediates axon growth inhibition

“…HDAC6 inhibition was previously shown to increase transport of mitochondria in axons of embryonic rodent hippocampal and chick sensory neurons (Chen et al, 2010; Kim et al, 2012; Rui and Zheng, 2016; Sainath et al, 2017), and axonal mitochondrial transport has been linked to axon growth (Steketee et al, 2012; Cartoni et al, 2016; Lewis et al, 2016; Zhou et al, 2016). By live-cell imaging with MitoTracker to visualize mitochondria, DRG neurons appeared to show increased anterograde versus retrograde mitochondrial movement along axons (Fig.…”

“…Acetyl-mimetic Miro1 K105Q mutant supports growth on these growth inhibitors and prevent decreases in mitochondrial transport and ψ M seen after exposure. CSPGs were also recently shown to impair mitochondria/ER targeting into growth cones of embryonic chick sensory neurons, with an accompanying decrease in ψ M (Sainath et al, 2017). This targeting deficit was suggested to disrupt functional linkages between mitochondria and ER.…”

Intrinsic mechanisms of neuronal axon regeneration

“…For example, ARMCX1 is a mammalian-specific gene that controls mitochondrial transport during neuronal repair 203 . Increased mitochondrial transport to injured axons is required for regeneration 203,204 , and CSPGs can prevent mitochondria from localizing to the growth cone 205 . There are also human-specific mRNA splice variants and human-specific genes in the nervous system that may play a role in the regenerative response 206–208 .…”

Genetic reduction of the extracellular matrix protein versican attenuates inflammatory cell infiltration and improves contractile function in dystrophic mdx diaphragm muscles

“…In cultured vascular endothelial cells, excess versican induced mitochondrial dysfunction when transported by exosomes to vascular smooth muscle cells 88 . Whilst, in cell culture models of axon growth, chondroitin sulphate proteoglycans, though not versican specifically, impaired mitochondrial respiration and decreased ATP synthesis through downstream deleterious effects on the mitochondrial membrane potential, mitochondrial biogenesis and morphology 89,90 . In the context of insulin resistance and diabetes, aberrant remodelling of the skeletal muscle extracellular matrix alters mechano-signal transduction, which, in turn, disrupts the expression of genes relevant to oxidative metabolism and mitochondrial biogenesis 91,92 .…”