Tag: ageing

Adjusting Microglia Proportions as a Basis for the Treatment of Parkinson’s Disease

The balance between different types of the immune cells known as macrophages is becoming a stronger theme these days, a line of research that falls somewhere into the broad overlap between regeneration, inflammation, and aging. I’ve seen quite a number of interesting papers on this topic in the past year, which seems to me a leap in the level of interest shown by the research community of late. While possibly oversimplifying a more complicated reality, we can think of macrophages as having a few different types, or polarizations. The M1 polarization tends towards aggressive destruction of problem cells, the creation of inflammation, and hindrance of regeneration. The M2 polarization tends towards suppression of inflammation and other behaviors that encourage regeneration. The cancer research community would like to be able to adjust macrophage populations towards the M1 type, more willing to destroy cancerous cells, while the regenerative medicine community would like to be able to adjust macrophage populations towards the M2 type to spur enhanced regeneration and tissue maintenance.

It may be that the increased interest in macrophage polarization is a function of the emergence of tools that now allow for cost-effective attempts to shift the balance of macrophage types. The infrastructure of biotechnology is advancing rapidly, and progress spurred by falling costs is a common theme in many parts of the field. Today I’ll offer up another example of macrophage polarization research, this time involving microglia, a form of macrophage resident in the central nervous system. Changes in microglia have been shown to be important in any number of age-related neurodegenerative conditions: the immune system declines with age in the brain, just as elsewhere in the body, falling into a dysfunctional and inflammatory state. This affects regeneration and tissue maintenance as is the case for macrophages beyond the brain, but microglia also have additional roles in the correct function of neurons and neural connections, an area of our biochemistry that is still comparatively poorly understood. It is possible to achieve benefits for patients by coercing more microglia into the M2, pro-regenerative polarization? In this open access paper, researchers examine the question in the context of Parkinson’s disease.

Targeting Microglial Activation States as a Therapeutic Avenue in Parkinson’s Disease

A growing body of evidence suggest that neuroinflammation mediated by microglia, the resident macrophage-like immune cells in the brain, play a contributory role in Parkinson’s disease (PD) pathogenesis. In the central nervous system (CNS), the innate immune response is predominantly mediated by microglia and astrocytes. Microglia play a vital role in both physiological and pathological conditions. Microglia appear to be involved in several regulatory processes in the brain that are crucial for tissue development, maintenance of the neural environment and, response to injury and promoting repair. Similar to peripheral macrophages, microglia directly respond to pathogens and maintain cellular homeostasis by purging said pathogens, as well as dead cells and pathological gene products.

Microglia participate in both physiological and pathological conditions. In the former, microglia restore the integrity of the central nervous system and, in the latter, they promote disease progression. Microglia acquire different activation states to modulate these cellular functions. When classically activated, microglia acquire the M1 phenotype, characterized by pro-inflammatory and pro-killing functions that serve as the first line of defense. The alternative M2 microglial activation state is involved in various events including immunoregulation, inflammation dampening, and repair and injury resolution.

Upon activation to the M1 phenotype, microglia elaborate pro-inflammatory cytokines and neurotoxic molecules promoting inflammation and cytotoxic responses. In contrast, when adopting the M2 phenotype microglia secrete anti-inflammatory gene products and trophic factors that promote repair, regeneration, and restore homeostasis. Relatively little is known about the different microglial activation states in PD, and the distribution of microglial M1/M2 phenotypes depends on the stage and severity of the disease. Understanding stage-specific switching of microglial phenotypes and the capacity to manipulate these transitions within appropriate time windows might be beneficial for PD therapy. The transition from the M1 pro-inflammatory state to the regulatory or anti-inflammatory M2 phenotype is thought to assist improved functional outcomes and restore homeostasis. The induction of M1 phenotype is a relatively standard response during injury. For peripheral immune cells it is thought that M1 polarization is terminal and the cells die during the inflammatory response. Although a shift from M1 to the M2 phenotype is considered rare for peripheral immune cells, microglia can shift from M1 to M2 phenotype.

To inhibit the pro-inflammatory damage through M1 activation of microglia, its downstream signaling pathways could be targeted. The M1 phenotype is induced by IFN-γ via the JAK/STAT signaling pathway and targeting this pathway may arrest M1 activation. In fact, studies show that inhibition of the JAK/STAT pathway leads to suppression of the downstream M1-associated genes in several disease models. Another approach to suppress M1 activation would be to target the pro-inflammatory cytokines such as TNF-α, IL-1β and IFN-γ, and decrease its ability to interact with its receptors on other cell types. Alternatively, molecules with the capability to activate the anti-inflammatory M2 phenotype or promote the transition of pro-inflammatory M1 phenotype to anti-inflammatory M2 could be useful in the treatment of PD. Anti-inflammatory molecules such as IL-10 and beta interferons produce neuroprotection by altering the M1 and M2 balance.

The critical role of microglia in most neurodegenerative pathologies including PD is increasingly documented through many studies. Until recently, microglial activation in pathological conditions was considered to be detrimental to neuronal survival in the substantia nigra of PD brains. Recent findings highlight the crucial physiological and neuroprotective role of microglia and other glial cells in neuropathological conditions. Studies on anti-inflammatory treatments targeting neuroinflammation in PD and other diseases by delaying or blocking microglial activation failed in many trials due to the lack of a specific treatment approach, possibly the stage of disease and an incorrect understanding of mechanisms underlying microglial activation. With the updated knowledge on different microglial activation states, drugs that can shift microglia from a pro-inflammatory M1 state to anti-inflammatory M2 state could be beneficial for PD. The M1 and M2 microglial phenotypes probably need further characterization, particularly in PD pathological conditions for better therapeutic targeting. We support targeting of microglial cells by modulating their activation states as a novel therapeutic approach for PD.


Evolutionary Trade-Offs in Stem Cell Populations: Repair Capacity versus Cancer Risk

This open access paper makes an interesting companion piece to yesterday’s discussion of the potential for expansion of mutations in stem cell populations to contribute to degenerative aging. What evolutionary constraints have led to the present state of stem cell populations in mammals: why are they not larger, with more capacity for tissue maintenance and regeneration in later life, for example?

Multicellular organisms continually accumulate mutations within their somatic tissues, constituting a significant, but poorly quantified, burden on tissue maintenance. To investigate this burden in a specific, well-parameterized context, we model the mammalian intestine and quantify the expected impact of mutation accumulation in stem cell populations. Furthermore, we explore how the population size of the stem cell niche influences mutation accumulation and demonstrate the expected trade-off between the risk of accumulating deleterious mutations, population size, and the risk of tumorigenesis. However, we further characterize how this trade-off can be expected to manifest over the lifetime of two well-studied mammalian systems, mice and humans, by estimating the expected effect of mutation accumulation on cellular homeostasis.

The intestinal epithelium is in constant flux, with populations of stem cells distributed throughout the intestine differentiating into other, transient, cell populations. These stem cells exist within small discrete populations in intestinal crypts, a compartmentalization thought to have evolved as a mechanism to deter tumorigenesis, as cells accumulating mutations that are beneficial to cellular fitness have a physical hindrance to spreading throughout the tissue. However, small populations are subject to significant genetic drift, that is, random changes in allele frequency that eventually lead to fixation or loss, and less effective selection.

The accumulation of damage causing the loss of cellular fitness is a hallmark of aging and is especially relevant when DNA damage occurs in stem cells, compromising their role in tissue renewal. Indeed, several mouse models with the diminished ability to maintain cellular genome integrity succumb to accelerated age-related phenotypes through the loss of tissue homeostasis caused by stem and progenitor cell attrition. Just as stem cell mutations conferring a beneficial fitness effect will increase cell production, mutations conferring a deleterious fitness effect will lead to decreased cell production and the diminished maintenance of healthy tissue.

When mutations confer a selective advantage or disadvantage within the niche, there exists an intermediate crypt size that minimizes the probability that any crypt accumulates the large beneficial mutations necessary to initiate a tumor. By modeling the fixation of mutations drawn from a full distribution of mutational effects and accumulating throughout the populations of the entire intestinal epithelium, we show that a secondary trade-off exists – populations maintained at a size that results in the lowest rate of tumorigenesis are expected to accumulate deleterious mutations that manifest in tissue attrition and contribute to organismal aging.

At small stem cell niche sizes, there exists a large number of crypts to maintain homeostasis, and a higher probability that any one crypt will obtain a rare mutation of large effect that would result in tumorigenesis. As stem cell niche size increases, the number of crypts needed to maintain the same amount of epithelium decreases, and so does the probability of fixing mutations within the crypts, and therefore the chance of fixing a rare mutation of large effect. However, for larger values of stem cell niche size, the strength of selection increases, thus increasing the chance that a fixed mutation was beneficial, leading to higher chances of tumorigenesis. At the observed intermediate population size in mice, the whole tissue size is expected to decline with age as deleterious mutations accumulate in stem cell niches. If selective pressures against tumorigenesis have selected for intermediate stem cell niche population sizes in mammalian species, then it has been at the expense of increasing epithelial attrition.

Link: http://bit.ly/2sWQP7u


Oisin Biotechnologies Launches New Website

Oisin Biotechnologies is a senescent cell clearance company founded by long-standing members of our community, seed funded by the Methuselah Foundation and SENS Research Foundation, and supported by the investment of a number of folk in the audience here. Targeted removal of senescent cells is a form of narrowly focused rejuvenation, shown to turn back numerous measures of aging in animal studies, and the Oisin team has made great strides in proving out their programmable gene therapy approach. This sort of commercialization project is exact what our community has been working towards all these years, and the faster that implementations reach the clinic, the better off we all are.

Oisin Biotechnologies’ ground-breaking research and technology is demonstrating that the solution to mitigating the effects of age-related diseases is to address the damage created by the aging process itself. Our first target is senescent cells. When cells detect that they have been irretrievably damaged, they enter a non-dividing condition known as cell-cycle arrest, or senescence. It’s believed this occurs to prevent cells from going rogue and turning cancerous. Ideally, they should die by the process known as apoptosis, but as we age, more and more frequently they don’t. They become zombie cells – unable to kill themselves or resume normal function.

Senescent cells secrete molecules that cause inflammation in an effort to attract immune cells that would usually clear them. But for reasons that are not fully known, as we age, persistently senescent cells accumulate, leading to a vast number of age-related diseases. Oisin is developing a highly precise, patent-pending, DNA-targeted intervention to clear these cells. As a recent study has shown, clearing senescent cells both reduces negative effects of aging pathologies and also extends median lifespan and survival.

There are two major challenges to clearing senescent cells using our approach. First is to design and create the DNA construct that recognizes that a cell has become senescent, and then destroys it. Second is to safely and efficiently deliver this construct into cells throughout the body. Both goals have been achieved in our pioneering proof of concept experiments in 2016. We’ve first demonstrated the ability to transduce cells both in vitro (cell culture) and in vivo (in aged mice). Then we showed that p16 positive senescent cells can be killed on demand in both in vitro and in vivo environments. Now we are embarked on experiments that will show improvements in both healthspan and lifespan in model organisms from mice to primates. And then, everything changes.

Our proprietary technology gives persistently senescent cells a helping hand to “do the right thing.” By providing an exogenous apoptotic gene, which is only transiently expressed in cells that already have the p16 gene active, we can precisely induce the senescent cell to commit suicide. Oisin has shown as much as an 80% reduction in senescent cells in cell culture and significant reductions of senescent cell burden in naturally aged mice. SENSOlytics is an Oisin proprietary platform technology that enables precise targeting of a senescent cell based on the DNA expression of the cell, not on surface markers or other characteristics that might be shared with normal, undamaged cells.

Link: http://bit.ly/2tRcLBh


Adjusting Macrophage Proportions as a Basis for the Treatment of Atherosclerosis

The immune cells known as macrophages are involved in debris cleanup and destruction of potentially harmful cells, among other tasks, but in recent years more attention has been drawn to the important role they play in the complex coordination of cellular activities relating to healing and tissue maintenance. It is even thought that a significant portion of the difference between limited human regeneration and proficient regeneration of the sort observed in salamanders might be explained by differences in macrophage behavior between these species.

Of more immediate practical use, macrophages involved in regenerative processes appear split into a few different classes with distinct behaviors and protein signatures. Although this is a case of arbitrary dividing lines drawn on a continuous spectrum rather than a case of clearly separate camps, it is a still a useful distinction to make. These types are known as polarizations, and the polarizations of interest in this discussion are M1 and M2. Both play important roles in the bigger picture, but M1 macrophages are generally less helpful in regeneration, spurring inflammation and fibrosis, while M2 macrophages are generally more helpful, suppressing inflammation and generating a more supportive environment for regrowth.

Researchers are finding that it is possible to enhance the outcome of regeneration by increasing the ratio of M2 macrophages to M1 macrophages. More M2 macrophages and fewer M1 macrophages produces more rapid, more effective regrowth of tissues, and in some cases induces regrowth that normally doesn’t occur with any reliability in mammals. This has been achieved in animal studies of nerve regeneration and bone healing, to pick a few examples. Interestingly, the cancer research community is interested in turning the dial in the opposite direction, generating more of the aggressive, inflammatory M1 macrophages that destroy cancer cells. As I said, both types have their part to play in the bigger picture.

Moving on to the topic at hand here today, the research below covers the impact of polarization on another part of the macrophage task list, that of debris clearance. Atherosclerosis is a condition in which oxidized, fatty metabolic waste enters the blood stream and sufficiently irritates a section of the blood vessel walls for the cells there to take action. Inflammatory signals draw macrophages that attempt to clean up the garbage, but macrophages are unfortunately unexpectedly frail in the face of this sort of fatty debris. Some ingest too much and either die or become senescent, dysfunctional foam cells, further aggravating the situation. Over time, a small irritated portion of a blood vessel wall swells into a self-perpetuating disaster zone of dead and dying macrophages. Eventually this happens somewhere critical, and driven by the hypertension of aging, a blood vessel wall or the fatty mass inside the vessel ruptures to cause a stroke or heart attack. It turns out that here, as elsewhere, it is the case that adjusting the natural balance towards more M2 and fewer M1 macrophages produces better outcomes, but just how useful this is for human medicine remains to be determined with any great certainty.

Mechanism Shown to Reverse Disease in Arteries

A certain immune reaction is the key, not to slowing atherosclerosis as cholesterol-lowering drugs do, but instead to reversing a disease that gradually blocks arteries to cause heart attacks and strokes. The study in mice focuses on reversing the effects of “bad cholesterol,” which is deposited into the walls lining blood vessels in levels influenced by both genetics and a person’s diet. By the fourth decade of life, and thanks to the chronic reaction to cholesterol, most people have inflamed “wounds” in their arteries, called plaques, which when severe enough can rupture to cause blood clots that block arteries. “Even the latest, most potent cholesterol-lowering drugs, PCSK9 inhibitors, let alone widely used statins, cannot fully reverse damage done to arteries over time. We need the next generation of drugs to go beyond cholesterol lowering to address the immune reaction to accumulated cholesterol, and to dismantle plaques as part of reversing or regressing mature disease.”

Once deposited into arteries, bad cholesterol – known to physicians as low density lipoprotein – triggers the body’s immune system, which is meant to destroy invading microbes but can drive inflammatory disease in the wrong context. Immune cells in the bloodstream called monocytes swarm to cholesterol deposits, and become either inflammatory or healing cell types based on signals there. In situations where disease is worsening in a plaque, past studies have shown that monocytes become M1 macrophages that amplify immune responses, increase inflammation, and secrete enzymes that gnaw at plaques until they rupture. The current study confirmed that monocytes arriving in plaques where disease is regressing instead become M2 “healing” macrophages, which dampen inflammation and prevent the ruptures that precede clotting.

When mice were engineered to lose the ability of monocytes to become M2 macrophages, they could no longer achieve normal disease regression. By surgically transplanting plaques from diseased mice into the arteries of healthy mice, the research team brought about dramatic drops in cholesterol levels. This drop has been shown to trigger a second benefit in mice, where monocytes automatically become M2 instead of M1 macrophages as plaques rapidly regress. It is not known whether cholesterol lowering alone triggers this M2 switch in humans, but new imaging techniques may soon be able to detect changes in the type and number of macrophages in plaques. In the meantime, if researchers learn how to boost the M2 switch, a number of clinical applications may become possible just as methods arrive that can measure their success. “A race is underway to develop treatments that enhance the decision of human monocytes to become M2 macrophages in cases where the disease has not yet caused clot formation, at which point it becomes irreversible.”

Inflammatory Ly6Chi monocytes and their conversion to M2 macrophages drive atherosclerosis regression

Using a number of mouse models of atherosclerosis regression, including the aortic arch transplant used in the present study, we have previously shown that aggressive lipid lowering promotes the resolution of plaque inflammation, which is characterized by a decreased content of macrophages and an increase in the level of markers of the M2 state. We now extend these findings to show that plaque regression and the attendant resolution of inflammation surprisingly require the recruitment of new monocytes, which assume the characteristics of M2 macrophages. Furthermore, contrary to the prevailing paradigm, the newly recruited monocytes are drawn from the Ly6Chi circulating subset, generally considered to be “inflammation-prone” precursors of M1 macrophages.

The characteristic rapid reversal of hyperlipidemia in mouse atherosclerosis regression models is likely to reduce the continuous stimulation of the plaque inflammatory response by atherogenic lipoproteins, but clearly is not sufficient for the resolution of inflammation. Based on our results, M2 enrichment must also occur, and how the change in lipoprotein environment causes this to happen also remains to be determined. Our finding that it depends on STAT6-dependent signaling in the newly recruited monocytes suggests that local factors in the regressing plaque stimulate this signaling pathway. STAT6 is activated by two key cytokines, IL-4 and IL-13. However, which of these cytokines is the main player, as well as their cellular source(s), in promoting plaque regression is unclear.

Though many questions remain, the present results provide insights into the dynamic nature of the inflammatory process and the role of Ly6Chi monocytes in plaques. These cells were previously thought to contribute only to plaque progression and inflammation, but are now shown here to be important in regression and inflammation resolution. One clinically relevant insight raised by our studies is that strategies that promote the accumulation of M2 macrophages in atherosclerotic lesions may be a promising approach toward promoting plaque regression, consistent with recent studies in mice in which treatment with IL-13- or IL-4-based therapy was protective against atherosclerosis progression.