By Bethany Veo, PhD
Mitochondria are most commonly known as the power houses of the cell, facilitating major functions such as oxidative phosphorylation and cellular respiration. Maintenance of mitochondria is essential to a cells' physiological homeostasis and requires oversight by several factors. PINK1 is a serine/threonine protein kinase which localizes to the mitochondrion and regulates its function and turnover by sensing when mitochondria are damaged.1 The foremost mechanisms of mitochondrial health upkeep include fusion and fission, mitophagy, and mitochondrial transport. PINK1 is critical for mitochondrial health by facilitating all of these pathways, which serve as a quality control system to remove dysfunctional or damaged mitochondrion from the cell. In fact, mutations in PINK1 are linked with Parkinson's disease, where dysfunction in mitophagy, mitochondrial clearance and neuroinflammation contribute to the disease.1
PINK1 was detected in immersion fixed paraffin-embedded sections of human brain (cortex) using 15 µg/mL Rat Anti-Human PINK1 Monoclonal Antibody (Catalog # MAB4357) overnight at 4 °C. Before incubation with the primary antibody tissue was subjected to heat‑induced epitope retrieval using Antigen Retrieval Reagent-Basic (Catalog # CTS013). Tissue was stained with the Anti‑Rat HRP-DAB Cell & Tissue Staining Kit (brown; Catalog # CTS017) and counterstained with hematoxylin (blue). View our protocol for Chromogenic IHC Staining of Paraffin-embedded Tissue Sections.
Mitochondrial transport supplies energy to the subcellular compartments of the cell that need it most. In neurons, where axon terminals and dendrites are not in close proximity to the cell body, mitochondrial motility is a necessity. For example, defects in mitochondrial motility have been implicated in neurodegeneration. Under conditions of oxidative stress, PINK1 regulates mitochondrial motility by phosphorylating Miro1, a GTPase that regulates mitochondrial transport via connection with motor proteins dynein and kinesin.1 Phosphorylation of Miro1 stalls the mitochondria leading to degradation of Miro1 by PARKIN (ubiquitin ligase) and removal of damaged mitochondria by autophagic mechanisms at the axon. Interestingly, a Miro1 knockout mouse shows similar developmental abnormalities as those observed in motor neuron disease, illustrating the importance of this pathway for mitochondrial homeostasis in neurons.1,2 However, the involvement of PINK1 in mitochondrial transport goes beyond phosphorylation of Miro1, indeed PINK1 has been linked to the stimulation of dendritic growth through enhancement of PKA signaling.3
In a new study, PINK1 deficient cortical neurons were utilized in live cell imaging and immunofluorescence with a MAP2 antibody to correlate the loss of PINK1 with defects in mitochondrial motility and decreased dendritic length.3 The authors determined that PKA, which is recruited to the mitochondrial membrane through activation by cytosolic PINK1, can enhance mitochondrial transport in dendrites. Additionally, they identified Miro2, another mitochondrial GTPase, which can stimulate mitochondrial movement in neurons from PINK1 deficient and wild-type mice by acting as a substrate for PKA activity. Phosphorylation of Miro2 by either PINK1 or PKA could activate mitochondrial transport towards the synapse.3
This study further defines the role of PINK1 by identifying additional factors (PKA and Miro2) that are interdependent on PINK1 to mediate mitochondrial transport as well as dendritic growth. Moreover, PINK1 was found to serve a dual role maintaining mitochondrial transport while facilitating removal of damaged mitochondria.
