Systemic human CD34(+) cells populate the brain and activate host mechanisms to counteract nigrostriatal degeneration

Umbilical cord blood derived cell expansion: a potential neuroprotective therapy

Umbilical cord blood (UCB) is a rich source of beneficial stem and progenitor cells with known angiogenic, neuroregenerative and immune-modulatory properties. Preclinical studies have highlighted the benefit of UCB for a broad range of conditions including haematological conditions, metabolic disorders and neurological conditions, however clinical translation of UCB therapies is lacking. One barrier for clinical translation is inadequate cell numbers in some samples meaning that often a therapeutic dose cannot be achieved. This is particularly important when treating adults or when administering repeat doses of cells. To overcome this, UCB cell expansion is being explored to increase cell numbers. The current focus of UCB cell expansion is CD34+ haematopoietic stem cells (HSCs) for which the main application is treatment of haematological conditions. Currently there are 36 registered clinical trials that are examining the efficacy of expanded UCB cells with 31 of these being for haematological malignancies. Early data from these trials suggest that expanded UCB cells are a safe and feasible treatment option and show greater engraftment potential than unexpanded UCB. Outside of the haematology research space, expanded UCB has been trialled as a therapy in only two preclinical studies, one for spinal cord injury and one for hind limb ischemia. Proteomic analysis of expanded UCB cells in these studies showed that the cells were neuroprotective, anti-inflammatory and angiogenic. These findings are also supported by in vitro studies where expanded UCB CD34+ cells showed increased gene expression of neurotrophic and angiogenic factors compared to unexpanded CD34+ cells. Preclinical evidence demonstrates that unexpanded CD34+ cells are a promising therapy for neurological conditions where they have been shown to improve multiple indices of injury in rodent models of stroke, Parkinson's disease and neonatal hypoxic ischemic brain injury. This review will highlight the current application of expanded UCB derived HSCs in transplant medicine, and also explore the potential use of expanded HSCs as a therapy for neurological conditions. It is proposed that expanded UCB derived CD34+ cells are an appropriate cellular therapy for a range of neurological conditions in children and adults.

α-Syn overexpression, NRF2 suppression, and enhanced ferroptosis create a vicious cycle of neuronal loss in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, affecting millions each year. Most PD cases (∼90%) are sporadic, resulting from the age-dependent accumulation of pathogenic effects. One key pathological hallmark of PD progression is the accumulation of alpha-synuclein (α-syn), which has been shown to negatively affect neuronal function and viability. Here, using 3- and 6-month-old Nrf2^+/+ and Nrf2^-/- mice overexpressing human α-syn (PD model), we show that loss of NRF2 increases markers of ferroptosis across PD-relevant brain regions. Increased ferroptosis was associated with an age- and genotype-dependent increase in α-syn pathology and behavioral deficits. Finally, we demonstrate that α-syn overexpression sensitizes neuronal cells and ex vivo brain slices to ferroptosis induction, which may be due to α-syn decreasing NRF2 protein levels. Altogether, these results indicate that NRF2 is a critical anti-ferroptotic mediator of neuronal survival, and that the vicious cycle of α-syn overexpression and NRF2 suppression, leading to enhanced neuronal ferroptotic cell death, could represent a targetable and currently untapped means of preventing PD onset and progression.

Design and Synthesis of Brain Penetrant Glycopeptide Analogues of PACAP With Neuroprotective Potential for Traumatic Brain Injury and Parkinsonism

There is an unmet clinical need for curative therapies to treat neurodegenerative disorders. Most mainstay treatments currently on the market only alleviate specific symptoms and do not reverse disease progression. The Pituitary adenylate cyclase-activating polypeptide (PACAP), an endogenous neuropeptide hormone, has been extensively studied as a potential regenerative therapeutic. PACAP is widely distributed in the central nervous system (CNS) and exerts its neuroprotective and neurotrophic effects via the related Class B GPCRs PAC1, VPAC1, and VPAC2, at which the hormone shows roughly equal activity. Vasoactive intestinal peptide (VIP) also activates these receptors, and this close analogue of PACAP has also shown to promote neuronal survival in various animal models of acute and progressive neurodegenerative diseases. However, PACAP's poor pharmacokinetic profile (non-linear PK/PD), and more importantly its limited blood-brain barrier (BBB) permeability has hampered development of this peptide as a therapeutic. We have demonstrated that glycosylation of PACAP and related peptides promotes penetration of the BBB and improves PK properties while retaining efficacy and potency in the low nanomolar range at its target receptors. Furthermore, judicious structure-activity relationship (SAR) studies revealed key motifs that can be modulated to afford compounds with diverse selectivity profiles. Most importantly, we have demonstrated that select PACAP glycopeptide analogues (2LS80Mel and 2LS98Lac) exert potent neuroprotective effects and anti-inflammatory activity in animal models of traumatic brain injury and in a mild-toxin lesion model of Parkinson's disease, highlighting glycosylation as a viable strategy for converting endogenous peptides into robust and efficacious drug candidates.

NRF2 Loss Accentuates Parkinsonian Pathology and Behavioral Dysfunction in Human α-Synuclein Overexpressing Mice

Nuclear factor (erythroid-derived 2)-like 2 (NRF2) is a central regulator of cellular stress responses and its transcriptional activation promotes multiple cellular defense and survival mechanisms. The loss of NRF2 has been shown to increase oxidative and proteotoxic stress, two key pathological features of neurodegenerative disorders such as Parkinson's disease (PD). Moreover, compromised redox homeostasis and protein quality control can cause the accumulation of pathogenic proteins, including alpha-synuclein (α-Syn) which plays a key role in PD. However, despite this link, the precise mechanisms by which NRF2 may regulate PD pathology is not clear. In this study, we generated a humanized mouse model to study the importance of NRF2 in the context of α-Syn-driven neuropathology in PD. Specifically, we developed NRF2 knockout and wild-type mice that overexpress human α-Syn (hα-Syn+/Nrf2-/- and hα-Syn+/Nrf2+/+ respectively) and tested changes in their behavior through nest building, challenging beam, and open field tests at three months of age. Cellular and molecular alterations in α-Syn, including phosphorylation and subsequent oligomerization, as well as changes in oxidative stress, inflammation, and autophagy were also assessed across multiple brain regions. It was observed that although monomeric α-Syn levels did not change, compared to their wild-type counterparts, hα-Syn+/Nrf2-/- mice exhibited increased phosphorylation and oligomerization of α-Syn. This was associated with a loss of tyrosine hydroxylase expressing dopaminergic neurons in the substantia nigra, and more pronounced behavioral deficits reminiscent of early-stage PD, in the hα-Syn+/Nrf2-/- mice. Furthermore, hα-Syn+/Nrf2-/- mice showed significantly amplified oxidative stress, greater expression of inflammatory markers, and signs of increased autophagic burden, especially in the midbrain, striatum and cortical brain regions. These results support an important role for NRF2, early in PD progression. More broadly, it indicates NRF2 biology as fundamental to PD pathogenesis and suggests that targeting NRF2 activation may delay the onset and progression of PD.

Enhanced NRF2 expression mitigates the decline in neural stem cell function during aging

Although it is known that aging affects neural stem progenitor cell (NSPC) biology in fundamental ways, the underlying dynamics of this process are not fully understood. Our previous work identified a specific critical period (CP) of decline in NSPC activity and function during middle age (13–15 months), and revealed the reduced expression of the redox‐sensitive transcription factor, NRF2, as a key mediator of this process. Here, we investigated whether augmenting NRF2 expression could potentially mitigate the NSPC decline across the identified CP. NRF2 expression in subventricular zone (SVZ) NSPCs was upregulated via GFP tagged recombinant adeno‐associated viral vectors (AAV‐NRF2‐eGFP), and its cellular and behavioral effects compared to animals that received control vectors (AAV‐eGFP). The vectors were administered into the SVZs of aging rats, at time points either before or after the CP. Results indicate that animals that had received AAV‐NRF2‐eGFP, prior to the CP (11 months of age), exhibited substantially improved behavioral function (fine olfactory discrimination and motor tasks) in comparison to those receiving control viruses. Further analysis revealed that NSPC proliferation, self‐renewal, neurogenesis, and migration to the olfactory bulb had significantly increased upon NRF2 upregulation. On the other hand, increasing NRF2 after the CP (at 20 months of age) produced no notable changes in NSPC activity at either cellular or behavioral levels. These results, for the first time, indicate NRF2 pathway modulation as a means to support NSPC function with age and highlight a critical time‐dependency for activating NRF2 to enhance NSPC function.

A Role for Nrf2 Expression in Defining the Aging of Hippocampal Neural Stem Cells

Redox mechanisms are emerging as essential to stem cell function given their capacity to influence a number of important signaling pathways governing stem cell survival and regenerative activity. In this context, our recent work identified the reduced expression of nuclear factor (erythroid-derived 2)-like 2, or Nrf2, in mediating the decline in subventricular zone neural stem progenitor cell (NSPC) regeneration during aging. Since Nrf2 is a major transcription factor at the heart of cellular redox regulation and homeostasis, the current study investigates the role that it may play in the aging of NSPCs that reside within the other major mammalian germinal niche located in the subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus. Using rats from multiple aging stages ranging from newborn to old age, and aging Nrf2 knockout mice, we first determined that, in contrast with subventricular zone (SVZ) NSPCs, Nrf2 expression does not significantly affect overall DG NSPC viability with age. However, DG NSPCs resembled SVZ stem cells, in that Nrf2 expression controlled their proliferation and the balance of neuronal versus glial differentiation particularly in relation to a specific critical period during middle age. Also, importantly, this Nrf2-based control of NSPC regeneration was found to impact functional neurogenesis-related hippocampal behaviors, particularly in the Morris water maze and in pattern separation tasks. Furthermore, the enrichment of the hippocampal environment via the transplantation of Nrf2-overexpressing NSPCs was able to mitigate the age-related decline in DG stem cell regeneration during the critical middle-age period, and significantly improved pattern separation abilities. In summary, these results emphasize the importance of Nrf2 in DG NSPC regeneration, and support Nrf2 upregulation as a potential approach to advantageously modulate DG NSPC activity with age.