Impairment of macroautophagy in dopamine neurons has opposing effects on Parkinsonian pathology and behavior

Parkinson’s disease (PD) is characterized by the death of dopamine neurons in the substantia nigra pars compacta (SNc) and accumulation of α-synuclein. Impaired autophagy has been implicated and activation of autophagy proposed as a treatment strategy. We generate a human α-synuclein-expressing mouse model of PD with macroautophagic failure in dopamine neurons to understand the interaction between impaired macroautophagy and α-synuclein. We find that impaired macroautophagy generates p62-positive inclusions and progressive neuron loss in the SNc. Despite this parkinsonian pathology, motor phenotypes accompanying human α-synuclein overexpression actually improve with impaired macroautophagy. Real-time fast-scan cyclic voltammetry reveals that macroautophagy impairment in dopamine neurons increases evoked extracellular concentrations of dopamine, reduces dopamine uptake, and relieves paired-stimulus depression. Our findings show that impaired macroautophagy paradoxically enhances dopamine neurotransmission, improving movement while worsening pathology, suggesting that changes to dopamine synapse function compensate for and conceal the underlying PD pathogenesis, with implications for therapies that target autophagy

Macroautophagy, alpha-synuclein and dopamine neurotransmission: implications for Parkinson’s disease

Parkinson’s disease (PD) is an incurable neurological disease characterised by impairment of motor function, death of substantia nigra pars compacta (SNc) dopamine (DA) neurons and accumulation of the protein α-synuclein. Macroautophagy, a major process by which deleterious cellular contents are degraded, is implicated in both sporadic and genetic PD, and macroautophagy inducers are currently in PD clinical trials. However, little is known about the interaction between α-synuclein and macroautophagy in vivo. In this thesis, the interaction between impaired macroautophagy in DA neurons and α-synuclein was studied by generating novel transgenic mice. Mice were bred featuring conditional knockout of ATG7, a gene essential for macroautophagy, in DA neurons (ATG7cKODAT-IRES-cre), and expressing the full-length human α-synuclein gene (hSNCA). Mice carrying the ATG7cKODAT-IRES-cre genotype developed key features of PD, including loss of SNc DA neurons, reductions in caudate-putamen DA and the development of protein aggregates in DA neurons. Presence of the hSNCA gene had minimal effect on histological phenotypes. Paradoxically, ATG7cKODAT-IRES-cre mice displayed improvements in some elements of motor function, including increased locomotion, increased gait swing speed and improved motor coordination in old age. There was no effect of the hSNCA gene on behavioural phenotypes. In order to determine a physiological basis for the discrepancy between the neuropathological and motor phenotypes associated with the ATG7cKODAT-IRES-cre genotype, DA neurotransmission was examined using fast-scan cyclic voltammetry (FCV). FCV demonstrated that the ATG7cKODAT-IRES-cre genotype increased evoked DA levels, reduced the rate of DA reuptake, and increased evoked DA in response to repeated stimuli. The finding that impaired macroautophagy in DA neurons enhances DA neurotransmission was confirmed in a second transgenic mouse model. These data demonstrating that impaired macroautophagy enhances dopamine neurotransmission, thus improving behavioural phenotypes while worsening some pathological phenotypes, has direct implications for PD pathogenesis, drug discovery and clinical trials.</p

Challenges in the Australasian neurosurgery training program: who should be trained and where should they train?

OBJECTIVE: Neurosurgical training poses particular challenges in Australia and New Zealand, given the large landmass, small population, and widely separated, often small, neurosurgical units. Such factors have necessitated a move away from autonomous, single-institution-based training to the selection of trainees by a centralized binational process. The success of this system is based on rigorous standardized evaluation of candidates' academic achievements, anatomical knowledge, references, and interview performance. Similarly, the accreditation of hospitals to train successful candidates has been standardized. The authors review the evolution of trainee selection and the accreditation of training posts in Australia and New Zealand. METHODS: The records of the Neurosurgical Society of Australasia Surgical Education and Training Board were reviewed for documents pertaining to the selection of neurosurgical trainees and the accreditation of training posts. Application records and referee scores from 2014 to the present were reviewed to encompass process changes, in particular the change from written referee reports to standardized interviews of referees. Surgical logbook case numbers for 23 trainees completing training in 2016, 2017, and 2018 were collated and presented in an aggregated, de-identified form as a measure of adherence to accreditation standards. Written evaluations of the training experience were also sought from two trainees reflecting on the selection process, the quality of training posts, and training limitations. RESULTS: While a time-consuming process, the method of obtaining referee reports by interview has resulted in a wider spread of scores, more able to separate high- and low-scoring applicants than other components of the selection process. Review of the training post accreditation records for the last 2 years showed that adherence to standards has resulted in loss of accreditation for one unit and shortened periods of review for units with more minor deficiencies. Two applications for accreditation have been denied. Examination of caseload data showed that trainees more than fulfill minimum requirements in accredited training posts, confirming the robust nature of this aspect of unit accreditation. CONCLUSIONS: A key factor determining the success of neurosurgical training in Australia and New Zealand has been a willingness to evolve selection and other processes to overcome challenges as they become apparent. According to available analyses, the revised referee process and strict accreditation standards appear effective. The benefits and challenges of the current training system are discussed in the context of a paucity of international literature

Behavioural characterisation of Macrod1 and Macrod2 knockout mice

Adenosine diphosphate ribosylation (ADP-ribosylation; ADPr), the addition of ADP-ribose moieties onto proteins and nucleic acids, is a highly conserved modification involved in a wide range of cellular functions, from viral defence, DNA damage response (DDR), metabolism, carcinogenesis and neurobiology. Here we study MACROD1 and MACROD2 (mono-ADP-ribosylhydrolases 1 and 2), two of the least well-understood ADPr-mono-hydrolases. MACROD1 has been reported to be largely localized to the mitochondria, while the &lt;i&gt;MACROD2&lt;/i&gt; genomic locus has been associated with various neurological conditions such as autism, attention deficit hyperactivity disorder (ADHD) and schizophrenia; yet the potential significance of disrupting these proteins in the context of mammalian behaviour is unknown. Therefore, here we analysed both &lt;i&gt;Macrod1&lt;/i&gt; and &lt;i&gt;Macrod2&lt;/i&gt; gene knockout (KO) mouse models in a battery of well-defined, spontaneous behavioural testing paradigms. Loss of &lt;i&gt;Macrod1&lt;/i&gt; resulted in a female-specific motor-coordination defect, whereas &lt;i&gt;Macrod2&lt;/i&gt; disruption was associated with hyperactivity that became more pronounced with age, in combination with a bradykinesia-like gait. These data reveal new insights into the importance of ADPr-mono-hydrolases in aspects of behaviour associated with both mitochondrial and neuropsychiatric disorders