👤 Sivaraj Sivaramakrishnan

BackgroundHigh intensity interval training (HIIT) involves vigorous intensity exercise bouts interspersed with low intensity bouts. Despite growing interest, the optimal dosage and clinical adaptability of HIIT in Parkinson's disease (PD) remain unclear. This scoping review synthesized the literature on systemic adaptations underlying HIIT in PD and developed a clinical framework while considering chronotropic incompetence, orthostatic hypotension, and disease progression.MethodsThree databases were searched for studies that incorporated HIIT interventions in PD. The Template for Intervention Description and Replication checklist was used to characterize the quality of intervention reporting.ResultsA total of 285 studies were screened, of which 10 studies were included. HIIT was administered 2-3 times/week for 30-60 min/session over 8-12 weeks. Seven studies used moderate-volume HIIT and three studies used high-volume HIIT protocols. The quality of intervention reporting was fair to good. HIIT improved cardiorespiratory fitness, motor severity, and functional mobility in PD, however, improvements were comparable to moderate intensity continuous training (MICT). HIIT may facilitate neuroplasticity by increasing brain-derived neurotrophic factor levels and dopamine transporter uptake. We recommend that HIIT programs for individuals with autonomic dysfunction use individualized heart rate targets, and perceived exertion for determining exercise intensity, and incorporate longer duration programs (>12 weeks).ConclusionHIIT is a well-tolerated intervention that may improve cardiorespiratory fitness, disease severity, and certain neurobiological markers in mild-moderate PD, with benefits similar to MICT. Larger trials comparing different HIIT volumes are needed to identify optimal exercise volume to inform individualized exercise prescription. Show less

Glucose-dependent insulinotropic peptide receptor (GIPR) stimulates insulin release and regulates metabolic homeostasis. GIPR function is shaped by spatiotemporal trafficking of this G protein-coupled receptor (GPCR). While GPCR endocytosis is traditionally associated with β-arrestin, GIPR internalization is only modestly dependent on this pathway. In this study, we demonstrate that GIPR engages a cytoskeletal motor, myosin VI to drive receptor endocytosis. GIPR engages the adaptor-motor complex through a PDZ-binding motif (PBM) at its C-ail. Interestingly, β-arrestin binding to phosphorylated residues upstream of the PBM enhance myosin VI recruitment and activation. GIPR internalization is dependent on both receptor phosphorylation and the PBM site to recruit β-arrestin and myosin VI, respectively. Synergistic engagement of β-arrestin and myosin VI results in desensitization of GIP-stimulated cAMP signaling while activating pERK1/2 from endosomal compartments. Blocking myosin VI activity enhances insulin release in pancreatic beta cells, demonstrating a novel role for this pathway in regulating the physiological effects of GIPR. Our findings highlight the direct convergence of two independent trafficking pathways at the level of the receptor C-tail, with implications for the nuanced regulation of individual GPCRs through the differential engagement of β-arrestin and myosin VI. GIPR has emerged as a frontline drug target in type 2 diabetes and obesity. Cellular effects of GIPR are regulated by receptor internalization and desensitization through mechanisms that are unclear. Here, we identify a novel GIPR trafficking pathway through the engagement of a cytoskeletal motor, myosin VI. Myosin VI and β-arrestin synergistically regulate GIPR endocytosis, signaling and insulin response in pancreatic beta cells. Our study highlights the convergence of two parallel trafficking mechanisms in GPCR function with potential implications in targeting metabolic disorders. Show less