Mathematical and experimental approaches to identify and predict the effects of chemotherapy on neuroglial precursors

Cross-translational models of late-onset cognitive sequelae and their treatment in pediatric brain tumor survivors

Pediatric brain tumor treatments have a high success rate, but survivors are at risk of cognitive sequelae that impact long-term quality of life. We summarize recent clinical and animal model research addressing pathogenesis or evaluating candidate interventions for treatment-induced cognitive sequelae. Assayed interventions encompass a broad range of approaches, including modifications to radiotherapy, modulation of immune response, prevention of treatment-induced cell loss or promotion of cell renewal, manipulation of neuronal signaling, and lifestyle/environmental adjustments. We further emphasize the potential of neuroimaging as a key component of cross-translation to contextualize laboratory research within broader clinical findings. This cross-translational approach has the potential to accelerate discovery to improve pediatric cancer survivors' long-term quality of life.

Mechanisms of Chemotherapy-Induced Neurotoxicity

Since the first clinical trials conducted after World War II, chemotherapeutic drugs have been extensively used in the clinic as the main cancer treatment either alone or as an adjuvant therapy before and after surgery. Although the use of chemotherapeutic drugs improved the survival of cancer patients, these drugs are notorious for causing many severe side effects that significantly reduce the efficacy of anti-cancer treatment and patients’ quality of life. Many widely used chemotherapy drugs including platinum-based agents, taxanes, vinca alkaloids, proteasome inhibitors, and thalidomide analogs may cause direct and indirect neurotoxicity. In this review we discuss the main effects of chemotherapy on the peripheral and central nervous systems, including neuropathic pain, chemobrain, enteric neuropathy, as well as nausea and emesis. Understanding mechanisms involved in chemotherapy-induced neurotoxicity is crucial for the development of drugs that can protect the nervous system, reduce symptoms experienced by millions of patients, and improve the outcome of the treatment and patients’ quality of life.

Cognitive dysfunction in patients with nasopharyngeal carcinoma after induction chemotherapy

OBJECTIVE

This prospective study aimed to assess the incidence, details of the change of cognitive dysfunction, and predictive factors of cognitive function impairment associated with induction chemotherapy (IC) in nasopharyngeal carcinoma (NPC) patients.

METHOD

We prospectively included NPC patients who treated with IC from December 2018 to January 2020. Montreal cognitive assessment (MoCA) was used to measure cognitive function, and score less than 26 was defined as cognitive dysfunction. Multivariate logistic regression analysis was applied to assess the independent predictors associated with cognitive function impairment.

RESULTS

A total of 76 patients were recruited, 10 patients were excluded due to refusal or unable to finish the questionnaire, and 66 patients were analyzed in this study. The median age of the patients was 48.5 years (range, 24-69 years). There was 89.4% of patients received ≥3 circles of IC. For the entire group, 27.3% had cognitive dysfunction, of which attention, language, short-term memory, and orientation showed significant downward trends, while visuospatial/executive function, naming, and abstraction demonstrated no prominent decrease. In patients having cognitive function impairment, 77.8% of them occurred after the first circle of IC. Gender (P = 0.039) and education (P = 0.03) were significant predictors for cognitive dysfunction. Female patients (female vs. male: 50% vs. 20%) and patients with lower educational levels (lower vs. higher: 37.8% vs. 11.8%) were more likely to suffer cognitive dysfunction. In addition, age (P = 0.572) and chemotherapy circles (P = 0.68) had no association with cognitive dysfunction.

CONCLUSION

Approximately 25% of NPC patients suffered cognitive dysfunction after IC, especially in female patients and patients with lower educational levels.

Cognitive and brain structural changes in long-term oligodendroglial tumor survivors

BACKGROUND

We identify cognitive impairment and MRI structural brain changes in long-term oligodendroglial tumor survivors treated with radiation therapy (RT) alone (21%) or with chemotherapy (CT) (79%).

METHODS

Oligodendroglial tumor patients (based on the World Health Organization [WHO] 2007 classification) who completed RT ± CT at least 2 years before the study initiation, were classified into 3 groups according to the time treatment was completed: Group 1 = 2-5 years (n = 22), Group 2 = 6-10 years (n = 13), and Group 3 >10 years (n = 13). All patients had a cross-sectional neuropsychological evaluation (n = 48) and a longitudinal volumetric analysis (gray matter [GM; n = 34]) between postsurgical and last follow-up MRI. White matter (WM) changes on MRI were assessed using a qualitative scale.

RESULTS

There were no differences regarding tumor or treatment-related characteristics between groups. Six of 22 patients (27.3%) in Group 1; 5/13 (38.5%) in Group 2; and 9/13 (69.2%) in Group 3 had cognitive impairment that was considered severe in 3/22 patients (13.6%) in Group 1; 4/13 (30.8%) in Group 2; and 6/13 (46.2%) in Group 3. Patients in Groups 2 and 3 showed significant GM atrophy and more leukoencephalopathy than Group 1. Cognitive deficits were associated with brain atrophy and WM changes.

CONCLUSIONS

Long-term oligodendroglial tumor survivors who underwent standard RT ± CT treatment, mainly >5 years of its completion, present cognitive impairment, especially on memory and executive functions, associated with late GM and WM damage, thus highlighting the need of developing future strategies in patients with oligodendroglial tumor and long expected survival.

Cellular mechanisms and treatments for chemobrain: insight from aging and neurodegenerative diseases

Chemotherapy is a life-saving treatment for cancer patients, but also causes long-term cognitive impairment, or "chemobrain", in survivors. However, several challenges, including imprecise diagnosis criteria, multiple confounding factors, and unclear and heterogeneous molecular mechanisms, impede effective investigation of preventions and treatments for chemobrain. With the rapid increase in the number of cancer survivors, chemobrain is an urgent but unmet clinical need. Here, we leverage the extensive knowledge in various fields of neuroscience to gain insights into the mechanisms for chemobrain. We start by outlining why the post-mitotic adult brain is particularly vulnerable to chemotherapy. Next, through drawing comparisons with normal aging, Alzheimer's disease, and traumatic brain injury, we identify universal cellular mechanisms that may underlie the cognitive deficits in chemobrain. We further identify existing neurological drugs targeting these cellular mechanisms that can be repurposed as treatments for chemobrain, some of which were already shown to be effective in animal models. Finally, we briefly describe future steps to further advance our understanding of chemobrain and facilitate the development of effective preventions and treatments.

Emerging mechanistic underpinnings and therapeutic targets for chemotherapy-related cognitive impairment

PURPOSE OF REVIEW

Modern innovations in cancer therapy have dramatically increased the number of cancer survivors. An unfortunately frequent side-effect of cancer treatment is enduring neurological impairment. Persistent deficits in attention, concentration, memory, and speed of information processing afflict a substantial fraction of cancer survivors following completion of these life-saving therapies. Here, we highlight chemotherapy-related cognitive impairment (CRCI) and discuss the current understanding of mechanisms underlying CRCI.

RECENT FINDINGS

New studies emphasize the deleterious impact of chemotherapeutic agents on glial-glial and neuron-glial interactions that shape the form, function and plasticity of the central nervous system. An emerging theme in cancer therapy-related cognitive impairment is therapy-induced microglial activation and consequent dysfunction of both neural precursor cells and mature neural cell types. Recent work has highlighted the complexity of dysregulated intercellular interactions involving oligodendrocyte lineage cells, microglia, astrocytes, and neurons following exposure to traditional cancer therapies such as methotrexate. This new understanding of the mechanistic underpinnings of CRCI has elucidated potential therapeutic interventions, including colony-stimulating factor 1 receptor inhibition, TrkB agonism, and aerobic exercise.

SUMMARY

Traditional cancer therapies induce lasting alterations to multiple neural cell types. Therapy-induced microglial activation is a critical component of the cause of CRCI, contributing to dysregulation of numerous processes of neural plasticity. Therapeutic targeting of microglial activation or the consequent dysregulation of neural plasticity mechanisms are emerging.

Iatrogenic Neuropathology of Systemic Therapies

Administration of systemic antineoplastic agents can result in adverse neurologic events. We describe the clinicopathologic features and putative mechanisms underlying iatrogenic neuropathology of the central nervous system secondary to chimeric antigen receptor (CAR) T-cell therapy and conventional chemotherapy.

White matter changes in primary central nervous system lymphoma patients treated with high-dose methotrexate with or without rituximab

PURPOSE

White matter changes (WMCs) can develop following systemic chemotherapy in patients with primary central nervous system lymphomas (PCNSLs), but the frequency and extent of these changes is not well characterized. This single center retrospective semi-quantitative study was performed to determine the rate, timing and grade of WMC on MRI in adult patients with newly-diagnosed radiotherapy-naïve PCNSL undergoing treatment with high-dose methotrexate (HD-MTX) with or without the addition of rituximab (-R).

METHODS

Serial MRI scans of consecutive adult PCNSL patients treated with HD-MTX ± R were assessed for WMC comparing the pre-treatment to post-treatment scans utilizing a 0-to-8-point severity scoring system.

RESULTS

Forty-seven PCNSL patients treated with either HD-MTX-R (n = 34; median age 66, 50% male) or HD-MTX (n = 13; median age 53, 54% male) were included in the analysis. WMC were detected in 62% (95% CI 46-76%) overall, in 68% of the HD-MTX-R, and in 46% of the HD-MTX group. Among patients with WMC (n = 29), WMC were first detected at an average of 2.8 months from beginning of therapy in the HD-MTX-R versus at 10.7 months in the HD-MTX group. Average WMC non-zero scores when first detected following the start of treatment were 2.5 (± 1.1) in HD-MTX-R and 1.5 (± 0.6) in HD-MTX.

CONCLUSIONS

Development of WMC in PCNSL patients treated with MTX and MTX-R is common. WMC changes appear to be more frequent, occur earlier and are more extensive in patients treated with HD-MTX-R compared to HD-MTX. Prospective studies are required to determine whether WMC correlate with survival or neurocognitive outcomes.

Methotrexate Chemotherapy Induces Persistent Tri-glial Dysregulation that Underlies Chemotherapy-Related Cognitive Impairment

Chemotherapy results in a frequent yet poorly understood syndrome of long-term neurological deficits. Neural precursor cell dysfunction and white matter dysfunction are thought to contribute to this debilitating syndrome. Here, we demonstrate persistent depletion of oligodendrocyte lineage cells in humans who received chemotherapy. Developing a mouse model of methotrexate chemotherapy-induced neurological dysfunction, we find a similar depletion of white matter OPCs, increased but incomplete OPC differentiation, and a persistent deficit in myelination. OPCs from chemotherapy-naive mice similarly exhibit increased differentiation when transplanted into the microenvironment of previously methotrexate-exposed brains, indicating an underlying microenvironmental perturbation. Methotrexate results in persistent activation of microglia and subsequent astrocyte activation that is dependent on inflammatory microglia. Microglial depletion normalizes oligodendroglial lineage dynamics, myelin microstructure, and cognitive behavior after methotrexate chemotherapy. These findings indicate that methotrexate chemotherapy exposure is associated with persistent tri-glial dysregulation and identify inflammatory microglia as a therapeutic target to abrogate chemotherapy-related cognitive impairment. VIDEO ABSTRACT.

A branching process model of heterogeneous DNA damages caused by radiotherapy in in vitro cell cultures

This paper deals with the dynamic modeling and simulation of cell damage heterogeneity and associated mutant cell phenotypes in the therapeutic responses of cancer cell populations submitted to a radiotherapy session during in vitro assays. Each cell is described by a finite number of phenotypic states with possible transitions between them. The population dynamics is then given by an age-dependent multi-type branching process. From this representation, we obtain formulas for the average size of the global survival population as well as the one of subpopulations associated with 10 mutation phenotypes. The proposed model has been implemented into Matlab^© and the numerical results corroborate the ability of the model to reproduce four major types of cell responses: delayed growth, anti-proliferative, cytostatic and cytotoxic.

Subcritical Sevastyanov branching processes with nonhomogeneous Poisson immigration

We consider a class of Sevastyanov branching processes with non-homogeneous Poisson immigration. These processes relax the assumption required by the Bellman-Harris process which imposes the lifespan and offspring of each individual to be independent. They find applications in studies of the dynamics of cell populations. In this paper, we focus on the subcritical case and examine asymptotic properties of the process. We establish limit theorems, which generalize classical results due to Sevastyanov and others. Our key findings include novel LLN and CLT which emerge from the non-homogeneity of the immigration process.

Radiation-induced brain injury: low-hanging fruit for neuroregeneration

Brain radiation is a fundamental tool in neurooncology to improve local tumor control, but it leads to profound and progressive impairments in cognitive function. Increased attention to quality of life in neurooncology has accelerated efforts to understand and ameliorate radiation-induced cognitive sequelae. Such progress has coincided with a new understanding of the role of CNS progenitor cell populations in normal cognition and in their potential utility for the treatment of neurological diseases. The irradiated brain exhibits a host of biochemical and cellular derangements, including loss of endogenous neurogenesis, demyelination, and ablation of endogenous oligodendrocyte progenitor cells. These changes, in combination with a state of chronic neuroinflammation, underlie impairments in memory, attention, executive function, and acquisition of motor and language skills. Animal models of radiation-induced brain injury have demonstrated a robust capacity of both neural stem cells and oligodendrocyte progenitor cells to restore cognitive function after brain irradiation, likely through a combination of cell replacement and trophic effects. Oligodendrocyte progenitor cells exhibit a remarkable capacity to migrate, integrate, and functionally remyelinate damaged white matter tracts in a variety of preclinical models. The authors here critically address the opportunities and challenges in translating regenerative cell therapies from rodents to humans. Although valiant attempts to translate neuroprotective therapies in recent decades have almost uniformly failed, the authors make the case that harnessing human radiation-induced brain injury as a scientific tool represents a unique opportunity to both successfully translate a neuroregenerative therapy and to acquire tools to facilitate future restorative therapies for human traumatic and degenerative diseases of the central nervous system.

Predictors of cognitive decline in people with cancer undergoing chemotherapy

PURPOSE

The purpose of this study was to investigate the impact of demographic factors, disease/treatment-related factors, and psychological factors on cognitive function.

METHOD

A cross-sectional study was conducted. Participants were recruited from the oncology inpatient units of two hospitals. A convenience sample of 175 patients with cancer who underwent chemotherapy were recruited. The Everyday Cognition Scale (ECog), the Korean version of the Mini Mental State Examination (K-MMSE), Functional Assessment of Cancer Therapy-Fatigue (FACT-F) scale, Hospital Anxiety and Depression Scale (HADS), and a questionnaire to collect information about demographic, disease, and treatment information were completed.

RESULTS

More participants showed a mild decline in cognitive function and self-reported cognitive decline (39.4%) than had objectively confirmed decline (20%). Notably, 53.7-62.9% of the participants showed memory loss and a decline in divided attention. Demographic factors (age, sex), disease/treatment-related factors (chemotherapy cycles, fatigue), and psychological factors (depression) were predictors of cognitive decline in 49.6% of participants.

CONCLUSIONS

Old age and cumulative chemotherapy cycles were the main influential factors for objectively confirmed cognitive decline, and fatigue was the most common predictor of self-reported cognitive decline. Depression was one of the predictors of perceived cognitive decline, but it was not significant for objectively measured cognitive function. Thus, treatment-related factors such as fatigue had a greater impact on cognitive decline than psychological factors.

Evaluation of function and recovery of adipose-derived stem cells after exposure to paclitaxel

BACKGROUND AIMS

Adipose-derived stem cells (ASCs) are considered to play a positive role in wound healing as evidenced by their increasing use in breast reconstructive procedures. After chemotherapy for breast cancer, poor soft tissue wound healing is a major problem. In the present study, the functional capabilities and recovery of ASCs after exposure to chemotherapeutic agent paclitaxel (PTX) using in vitro and ex vivo models were demonstrated.

METHODS

Human ASCs were isolated from periumbilical fat tissue and treated with PTX at various concentrations. Adult Sprague-Dawley rats were given intravenous injections with PTX. Two and four weeks after the initial PTX treatment, ASCs were isolated from rat adipose tissue. Proliferation, cell viability, apoptosis and cell migration rates were measured by growth curves, MTT assays, flow cytometry and scratch assays. ASCs were cultured in derivative-specific differentiation media with or without PTX for 3 weeks. Adipogenic, osteogenic and endothelial differentiation levels were measured by quantitative reverse transcriptase polymerase chain reaction and histological staining.

RESULTS

PTX induced apoptosis, decreased the proliferation and cell migration rates of ASCs and inhibited ASCs multipotent differentiation in both in vitro human ASC populations and ex vivo rat ASC populations with PTX treatment. Furthermore, after cessation of PTX, ASCs exhibited recovery potential of differentiation capacity in both in vitro and animal studies.

CONCLUSIONS

Our results provide insight into poor soft tissue wound healing and promote further understanding of the potential capability of ASCs to serve as a cell source for fat grafting and reconstruction in cancer patients undergoing chemotherapy treatment.

[Effect of Cancer Symptoms and Fatigue on Chemotherapy-related Cognitive Impairment and Depression in People with Gastrointestinal Cancer]

PURPOSE

The purpose of this study was to test a hypothetical model of chemotherapy-related cognitive impairment (CRCI) and depression in people with gastrointestinal cancer.

METHODS

A purposive sample of 198 patients undergoing chemotherapy was recruited from November 2014 to July 2015. The instruments were Everyday Cognition (ECog), Hospital Anxiety Depression Scale (HADS), Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F), and M. D. Anderson Symptom Inventory-Gastrointestinal Cancer Module. Data were analyzed using descriptive statistics, correlation, and path analysis.

RESULTS

CRCI was directly affected by cancer symptoms (β=.19, p=.004) and fatigue (β=.56, p<.001)(R²=47.2%). Depression was directly affected by fatigue (β=.48, p<.001) and CRCI (β=.27, p<.001). However, The impact of cancer symptoms on depression was confirmed through the mediating effect of CRCI.

CONCLUSION

Results indicate that in patients with gastrointestinal cancer undergoing chemotherapy along with the direct physiologic effects (fatigue, symptoms) of cancer treatment may have altered cognitive function leading to depression.

Higher cardiorespiratory fitness levels are associated with greater hippocampal volume in breast cancer survivors

As breast cancer treatment is associated with declines in brain and cognitive health, it is important to identify strategies to enhance the cognitive vitality of cancer survivors. In particular, the hippocampus is known to play an important role in brain and memory declines following cancer treatment. The hippocampus is also known for its plasticity and positive association with cardiorespiratory fitness (CRF). The present study explores whether CRF may hold promise for lessening declines in brain and cognitive health of a sample of breast cancer survivors within 3 years of completion of primary cancer treatment. We explored the role of cardiovascular fitness in hippocampal structure in breast cancer survivors and non-cancer female controls, as well as performed a median split to compare differences in hippocampal volume in relatively higher fit and lower fit cancer survivors and non-cancer controls. Indeed, CRF and total hippocampal volume were positively correlated in the cancer survivors. In particular, higher fit breast cancer survivors had comparable hippocampal volumes to non-cancer control participants (Cohen's d = 0.13; p > 0.3), whereas lower fit breast cancer survivors showed significantly smaller hippocampal volumes compared to both lower fit and higher fit control participants (Cohen's d = 0.87, p < 0.05). These results are the first to identify that CRF may protect the brain health of breast cancer survivors within 3 years of treatment. The present study uniquely contributes to the field of cancer and cognition and emphasizes the importance of investigating how individual differences in CRF play a role in brain changes of breast cancer survivors.

Systemic chemotherapy decreases brain glucose metabolism

Objective

Cancer patients may experience neurologic adverse effects, such as alterations in neurocognitive function, as a consequence of chemotherapy. The mechanisms underlying such neurotoxic syndromes remain poorly understood. We here describe the temporal and regional effects of systemically administered platinum-based chemotherapy on glucose metabolism in the brain of cancer patients.

Methods

Using sequential FDG-PET/CT imaging prior to and after administration of chemotherapy, we retrospectively characterized the effects of intravenously administered chemotherapy on brain glucose metabolism in a total of 24 brain regions in a homogenous cohort of 10 patients with newly diagnosed non-small-cell lung cancer.

Results

Significant alterations of glucose metabolism were found in response to chemotherapy in all gray matter structures, including cortical structures, deep nuclei, hippocampi, and cerebellum. Metabolic changes were also notable in frontotemporal white matter (WM) network systems, including the corpus callosum, subcortical, and periventricular WM tracts.

Interpretation

Our data demonstrate a decrease in glucose metabolism in both gray and white matter structures associated with chemotherapy. Among the affected regions are those relevant to the maintenance of brain plasticity and global neurologic function. This study potentially offers novel insights into the spatial and temporal effects of systemic chemotherapy on brain metabolism in cancer patients.

Chemotherapy-related cognitive dysfunction: current animal studies and future directions

Cognitive impairment is a potential long-term side effect of adjuvant chemotherapy that can have a major impact on the quality of life of cancer survivors. There is a growing number of preclinical studies addressing this issue, thereby extending our knowledge of the mechanisms underlying chemotherapy-induced neurotoxicity. In this review, we will summarize the recent advances and important findings presented in these studies. Emerging challenges, such as the development of neuroprotective strategies, and the role of the blood-brain barrier on cognitive impairment will be described and future directions in this field of investigation will be outlined.

Neural correlates of chemotherapy-related cognitive impairment

Cancer survivors frequently experience cognitive deficits following chemotherapy. The most commonly affected functions include memory, attention and executive control. The present paper reviews animal research and clinical studies including event-related potential (ERP) and neuroimaging investigations of chemotherapy-related changes of brain structure and function. In rodents, chemotherapeutic substances have been shown to damage neural precursor cells and white matter tracts and are associated with impairments of learning and memory. Structural and functional changes associated with chemotherapy have also been observed in humans. Structural imaging has revealed gray and white matter volume reductions and altered white matter microstructure. Functional studies using either ERPs or hemodynamic imaging have shown that chemotherapy alters the activation patterns of cortical networks involved in higher cognitive functions. Collectively, these findings support the existence of the "chemobrain" phenomenon beyond the patients' subjective reports. However, the rather small number of studies and methodological limitations of some of the pioneering investigations call for further research of high methodological quality, including larger numbers of subjects with appropriate controls to delineate the temporal and spatial pattern of chemotherapy-associated central nervous system (CNS) toxicity. Brain activation studies in humans might systematically vary task difficulty levels to distinguish between compensatory hyper-activations on the one hand and deficient recruitment of resources on the other hand. Integrative functions could be tested by connectivity analyses using both electrophysiological and hemodynamic measures. The ultimate goal should be the development of cognitive-behavioral and pharmacological interventions to reduce the cognitive side effects of the medically indispensable but neurotoxic chemotherapeutic treatments.

Challenges in research on the neural basis of „chemobrain”

Cancer survivors treated with chemotherapy frequently complain about impairment of cognitive functions including attention and memory. While the contribution of factors like psychological distress, anxiety or fatigue to this “chemobrain” syndrome has been discussed, studies in rodents have demonstrated the toxicity of various chemotherapeutic substances to the adult central nervous system. In humans, structural brain imaging has revealed both reduced gray and white matter volume and decreased white matter integrity related to chemotherapeutic treatment. Studies of brain function have found alterations in brain activation patterns during different types of tasks. Nevertheless, further clinical research using prospective designs in larger samples is required to better understand the relationship between chemotherapy and cognitive deficits. Variables that need to be considered more systematically include drug dose, genetic variations, and psychological factors. Assessing both electroencephalographic and hemodynamic responses during tasks at different stages of the processing hierarchy and at different difficulty levels should help in pinpointing the cortical processes affected by chemotherapy.

Reduced hippocampal volume and verbal memory performance associated with interleukin-6 and tumor necrosis factor-alpha levels in chemotherapy-treated breast cancer survivors

Many survivors of breast cancer show significant cognitive impairments, including memory deficits. Inflammation induced by chemotherapy may contribute to hippocampal changes that underlie these deficits. In this cross-sectional study, we measured bilateral hippocampal volumes from high-resolution magnetic resonance images in 42 chemotherapy-treated breast cancer survivors and 35 healthy female controls. Patients with breast cancer were, on average, 4.8 ± 3.4 years off-therapy. In a subset of these participants (20 breast cancer, 23 controls), we quantified serum cytokine levels. Left hippocampal volumes and memory performance were significantly reduced and interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNFα) concentrations were significantly elevated in the breast cancer group compared to controls. In the breast cancer group, lower left hippocampal volume was associated with higher levels of TNFα and lower levels of IL-6 with a significant interaction between these two cytokines suggesting a potential modulatory effect of IL-6 on TNFα. Verbal memory performance was associated with cytokine levels and left hippocampal volume in both groups. These findings provide evidence of altered hippocampal volume and verbal memory difficulties following breast cancer chemotherapy that may be mediated by TNFα and IL-6.

Asymptotic behavior of cell populations described by two-type reducible age-dependent branching processes with non-homogeneous immigration()

Stem and precursor cells play a critical role in tissue development, maintenance, and repair throughout the life. Often, experimental limitations prevent direct observation of the stem cell compartment, thereby posing substantial challenges to the analysis of such cellular systems. Two-type age-dependent branching processes with immigration are proposed to model populations of progenitor cells and their differentiated progenies. Immigration of cells into the pool of progenitor cells is formulated as a non-homogeneous Poisson process. The asymptotic behavior of the process is governed by the largest of two Malthusian parameters associated with embedded Bellman-Harris processes. Asymptotic approximations to the expectations of the total cell counts are improved by Markov compensators.

Biological and mathematical modeling of melanocyte development

We aim to evaluate environmental and genetic effects on the expansion/proliferation of committed single cells during embryonic development, using melanoblasts as a paradigm to model this phenomenon. Melanoblasts are a specific type of cell that display extensive cellular proliferation during development. However, the events controlling melanoblast expansion are still poorly understood due to insufficient knowledge concerning their number and distribution in the various skin compartments. We show that melanoblast expansion is tightly controlled both spatially and temporally, with little variation between embryos. We established a mathematical model reflecting the main cellular mechanisms involved in melanoblast expansion, including proliferation and migration from the dermis to epidermis. In association with biological information, the model allows the calculation of doubling times for melanoblasts, revealing that dermal and epidermal melanoblasts have short but different doubling times. Moreover, the number of trunk founder melanoblasts at E8.5 was estimated to be 16, a population impossible to count by classical biological approaches. We also assessed the importance of the genetic background by studying gain- and loss-of-function β-catenin mutants in the melanocyte lineage. We found that any alteration of β-catenin activity, whether positive or negative, reduced both dermal and epidermal melanoblast proliferation. Finally, we determined that the pool of dermal melanoblasts remains constant in wild-type and mutant embryos during development, implying that specific control mechanisms associated with cell division ensure half of the cells at each cell division to migrate from the dermis to the epidermis. Modeling melanoblast expansion revealed novel links between cell division, cell localization within the embryo and appropriate feedback control through β-catenin.

Quasi- and pseudo-maximum likelihood estimators for discretely observed continuous-time Markov branching processes

This article deals with quasi- and pseudo-likelihood estimation in a class of continuous-time multi-type Markov branching processes observed at discrete points in time. "Conventional" and conditional estimation are discussed for both approaches. We compare their properties and identify situations where they lead to asymptotically equivalent estimators. Both approaches possess robustness properties, and coincide with maximum likelihood estimation in some cases. Quasi-likelihood functions involving only linear combinations of the data may be unable to estimate all model parameters. Remedial measures exist, including the resort either to non-linear functions of the data or to conditioning the moments on appropriate sigma-algebras. The method of pseudo-likelihood may also resolve this issue. We investigate the properties of these approaches in three examples: the pure birth process, the linear birth-and-death process, and a two-type process that generalizes the previous two examples. Simulations studies are conducted to evaluate performance in finite samples.

Cognitive side effects of cancer therapy demonstrate a functional role for adult neurogenesis

Cancer therapies frequently result in a spectrum of neurocognitive deficits that include impaired learning, memory, attention and speed of information processing. Damage to dynamic neural progenitor cell populations in the brain are emerging as important etiologic factors. Radiation and chemotherapy-induced damage to neural progenitor populations responsible for adult hippocampal neurogenesis and for maintenance of subcortical white matter integrity are now believed to play major roles in the neurocognitive impairment many cancer survivors experience.