Sex frailty differences in ageing mice: Neuropathologies and therapeutic projections.

It is well-established that females live longer than males. Paradoxically, women tend to have poorer health, a condition often named sex frailty. The aim of this study was to evaluate possible frailty predictors in older mice in a sex-specific manner, in order to employ these predictors to follow-up therapy efficiency. To further evaluate therapy effects, we also investigated the use of neurotrophic insulin-like growth factor 1 (IGF-1) gene therapy and its correlation with the expression of this frailty and emotional behaviour. In order to evaluate frailty, we employed two different approaches. We performed a frailty assessment through a 31-Item Clinical Frailty Index and through a Performance-Based 8-Item Frailty Index. Our results show that both indexes are in concordance to evaluate sex differences, but they do not correlate when evaluating IGF-1 therapy effects. Moreover, in order to reduce test-to-test variability for measures of dependent variables, we compared open field results across studies assessing sex and treatment by means of the z-score normalization. The data show that regular open field parameters submitted to z-score normalization analysis could be a useful tool to identify sex differences in ageing mice after growth factor therapies. Taking this into account, sex is a factor that influences the incidence and/or nature of all major complex diseases; the main outcome of our investigation is the development of an efficient tool that compares the use of different frailty index calculations. This represents an important strategy in order to identify sex differences and therapy efficiency in ageing models.

Intracisternal IGF-1 gene therapy abrogates kainic acid-induced excitotoxic damage of the rat spinal cord.

Development of alternative therapies for treating functional deficits after different neurological damages is a challenge in neuroscience. Insulin-like growth factor-1 (IGF-1) is a potent neurotrophic factor exerting neuroprotective actions in brain and spinal cord. It is used to prevent or treat injuries of the central nervous system using different administration routes in different animal models. In this study, we evaluated whether intracisternal (IC) route for IGF-1 gene therapy may abrogate or at least reduce the structural and behavioral damages induced by the intraparenchymal injection of kainic acid (KA) into the rat spinal cord. Experimental (Rad-IGF-1) and control (Rad-DsRed-KA) rats were evaluated using a battery of motor and sensory tests before the injection of the recombinant adenovector (day -3), before KA injection (day 0) and at every post-injection (pi) time point (days 1, 2, 3 and 7 pi). Histopathological changes and neuronal and glial counting were assessed. Pretreatment using IC delivery of RAd-IGF-1 improved animal's general condition and motor and sensory functions as compared to Rad-DsRed-KA-injected rats. Besides, IC Rad-IGF-1 therapy abrogated later spinal cord damage and reduced the glial response induced by KA as observed in Rad-DsRed-KA rats. We conclude that the IC route for delivering RAd-IGF-1 prevents KA-induced excitotoxicity in the spinal cord.

Intracerebroventricular streptozotocin induces impaired Barnes maze spatial memory and reduces astrocyte branching in the CA1 and CA3 hippocampal regions.

Sporadic Alzheimer's disease (SAD) is the most common form of dementia; therefore, there is an urgent need for a model that recapitulates the main pathologic hallmarks of this disease. The intracerebroventricular (icv) injection of streptozotocin (icv-STZ) in rats constitutes a promising model, and thus, icv-STZ rats develop insulin-resistant brain state and cognitive impairments. Even though a great piece of studies has hitherto described this system as a model for SAD, further behavioral and morphometric studies are still needed to fully characterize it. In this study, using Sprague Dawley rats, we evaluated short-term effects on behavior and hippocampus morphometry of the icv-STZ injection at two doses: 1 (STZ1) and 3 mg/kg (STZ3). We found that, following icv-STZ injection, STZ3 animals, but not STZ1, exhibited impairments in spatial reference learning and memory (Barnes maze test) and in recognition memory (object recognition test). Furthermore, the results from behavioral and morpho-histochemical data are compatible. STZ3 rats displayed Stratum Radiatum volume reduction and a decreased NeuN immunoreactivity (neuron loss) in hippocampal CA1 region, together with an increased immunoreactivity for microglial (Iba1) and astroglial (GFAP) markers (neuroinflammation). Sholl analysis revealed the vulnerability of hippocampal astrocytes to STZ in CA1 and CA3. Thus, both doses induced a reduction in process length and in the number of main processes, accompanied by a frank decrease in branching complexity. The present study provides important knowledge of this AD rat model. Overall, we found that the only high STZ dose induced severe and acute neurodegenerative lesions, associated with an inflammation process.

IGF-1 Gene Transfer Modifies Inflammatory Environment and Gene Expression in the Caudate-Putamen of Aged Female Rat Brain.

Brain aging is characterized by chronic neuroinflammation caused by activation of glial cells, mainly microglia, leading to alterations in homeostasis of the central nervous system. Microglial cells are constantly surveying their environment to detect and respond to diverse signals. During aging, microglia undergoes a process of senescence, characterized by loss of ramifications, spheroid formation, and fragmented processes, among other abnormalities. Therefore, the study of changes in microglia during is of great relevance to understand age-related declines in cognitive and motor function. We have targeted the deleterious effects of aging by implementing IGF-1 gene transfer, employing recombinant adenoviral vectors (RAds) as a delivery system. In this study, we performed intracerebroventricular (ICV) RAd-IGF-1 or control injection on aged female rats and evaluated its effect on caudate-putamen unit (CPu) gene expression and inflammatory state. Our results demonstrate that IGF-1 overexpression modified aged microglia of the CPu towards an anti-inflammatory condition increasing the proportion of double immuno-positive Iba1+Arg1+ cells. We also observed that phosphorylation of Akt was increased in animals treated with RAd-IGF-1. Moreover, IGF-1 gene transfer was able to regulate CPu pro-inflammatory environment in female aged rats by down-regulating the expression of genes typically overexpressed during aging. RNA-Seq data analysis identified 97 down-modulated DEG in the IGF-1 group as compared to the DsRed one. Interestingly, 12 of these DEG are commonly overexpressed during aging, and 9 out of 12 are expressed in microglia/macrophages and are involved in different processes that lead to neuroinflammation and/or neuronal loss. Finally, we observed that IGF-1 overexpression led to an improvement in motor functions. Although further studies are necessary, with the present results, we conclude that IGF-1 gene transfer is modifying both the pro-inflammatory environment and activation of microglia/macrophages in CPu. In this regard, IGF-1 gene transfer could counteract the neuroinflammatory effects associated with aging and improve motor functions in senile animals.

IGF1 gene therapy in middle-aged female rats delays reproductive senescence through its effects on hypothalamic GnRH and kisspeptin neurons.

The process of aging is the result of progressive loss of homeostasis and functional body impairment, including the central nervous system, where the hypothalamus plays a key role in regulating aging mechanisms. The consequences of aging include a chronic proinflammatory environment in the hypothalamus that leads to decreased secretion of gonadotropin-releasing hormone (GnRH) and impairs kisspeptin neuron functionality. In this work, we investigated the effect of insulin-like growth factor 1 (IGF1) gene therapy on hypothalamic kisspeptin/GnRH neurons and on microglial cells, that mediate the inflammatory process related with the aging process. The results show that IGF1 rats have higher kisspeptin expression in the anteroventral periventricular (AVPV) nucleus and higher immunoreactivity of GnRH in the arcuate nucleus and median eminence. In addition, IGF1-treated animals exhibit increased numbers of Iba1+ microglial cells and MHCII+/Iba1+ in the AVPV and arcuate nuclei. In conclusion, IGF1 gene therapy maintains kisspeptin production in the AVPV nucleus, induces GnRH release in the median eminence, and alters the number and reactivity of microglial cells in middle-aged female rats. We suggest that IGF1 gene therapy may have a protective effect against reproductive decline.

IGF1 Gene Therapy Modifies Microglia in the Striatum of Senile Rats.

Microglial cells become dystrophic with aging; this phenotypic alteration contributes to basal central nervous system (CNS) neuroinflammation being a risk factor for age related neurodegenerative diseases. In previous studies we have observed that insulin like growth factor 1 (IGF1) gene therapy is a feasible approach to target brain cells, and that is effective to modify inflammatory response in vitro and to ameliorate cognitive or motor deficits in vivo. Based on these findings, the main aim of the present study is to investigate the effect of IGF1 gene therapy on microglia distribution and morphology in the senile rat. We found that IGF1 therapy leads to a region-specific modification of aged microglia population.

Novel adenoviral IGF-1 administration modulates the association between depressive symptoms and aging: Does gender matter?

Depression is an illness of multifactorial origin and it seems to involve the dysregulation of many physiological processes. It also has been associated with age and a decreased in the expression of some neurotrophins. However, there are not unique animal models to assay depressive-like behavior, with male and females responding differently. In this study, we report the effects of gender on aged associated depressive signs as frailty, muscular strength and motor activity, as well as the role of intramuscular IGF-1 gene therapy in these processes. We found that male mice had higher general discomfort than females. Moreover, we observed that IGF-1 treatment did not modify this index in females. Regarding male mice, adenoviral IGF-1 injection reduced frailty scores compared to its adenoviral control. According to data, IGF-1 gene therapy had a positive effect on depressive associated hypo-locomotion activity as indicate by delta of total distance and the increment observed in time of mobility in male mice. This neurotrophic factor also increased the latency of time to fall in grip strength in male mice compared to female mice. Moreover, we observed that, while the therapy had no effect on the digging behavior, IGF-1 treatment diminished the latency to dig and increase the number of buried marbles in male mice, having no effect on female. The present study demonstrates that, in order to establish an animal model of depression both, gender and age are relevant variables/factors to consider. We also conclude that a frailty phenotype underlies depressive-like symptoms in an experimental mouse model. Furthermore, we demonstrated that intramuscular injection represents a less invasive, feasible and controllable route of IGF-1 gene delivery for the treatment of the depressive phenotype in old mice.