ECM stiffness
Figure 1: Therapeutic approaches for ECM stiffness. Areas with yellow highlight indicate target(s) not explored by existing companies. Company logo is followed by description of their approach, stage of development, and disease(s) they target.
Cells and tissues are embedded within the extracellular matrix (ECM), which provides structural support and facilitates intercellular communication. The ECM is made of collagen, glycoproteins, and proteoglycans, which are produced and released by cells. Cells also monitor and integrate signals from the ECM through mechanotransduction, and modify their environment by producing and remodeling the ECM.
With aging, the ECM becomes stiffer due to the accumulation of damaged ECM components, such as fragmented collagens, and protein aggregates. The stiffness is also caused by the progressive increase in enzymatic and stochastic non-enzymatic intra-intermolecular covalent bonds, or crosslinks, between molecules with slow turnovers, resulting in advanced glycation end products (AGEs). This stiffness impairs tissue function, alters cell behaviors, and contributes to age-related diseases, such as osteoarthritis, cardiovascular disease, and pulmonary fibrosis.
To combat the effects of ECM stiffness, four approaches can be used.
ECM components
Supplementing ECM components that decrease with aging or removing damaged components represent a strategy for rejuvenating the aged ECM
1.1. Elastin
Elastin is one of the major components of the ECM and provides elasticity and flexibility to various organs. With aging, elastin loses elasticity, becomes fragmented, and its production decreases, leading to cardiovascular diseases and cognitive impairment (Fedintsev and Moskalev 2020).
To address this issue, Elastrin is developing a nanoparticle therapy that targets damaged elastin. This approach allows for effective delivery of active agents, such as EDTA to de-calcify tissue, and PGG to promote the formation of new, healthy elastin, thus restoring tissue elasticity and potentially improving the symptoms of age-related diseases.
1.2. collagen
Collagen makes up the majority of the ECM. There are 28 types of collagen in humans, with Type I collagen being the most abundant, making up approximately 90% of the total collagen content (Shoulders and Raines 2009).
It has been shown that supplementing diets with collagen peptides increases lifespan in C. elegans and Sprague-Dawley rats (Morikiri et al. 2018, Liang et al. 2010). However, how collagen content affects aging also depends on tissue type. In skin, collagen undergoes progressive loss and fragmentation with age, and delivering type I collagen mRNA in vivo rejuvenates the skin of photoaged mice (You et al. 2023). On the other hand, increased deposition of type I collagen contributes to lung fibrosis (Kleaveland et al. 2014). Therefore, strategies for adding or removing collagen as a way to combat ECM stiffness are dependent on tissue type.
Jeune is developing gene therapy using HSV-1 viral vectors to deliver type III collagen for skin aging. Anima Biotech is creating mRNA modulators to inhibit type I collagen for fibrosis.
1.3. Hyaluronic acid
Hyaluronic acid (hyaluronan) is an ECM component that maintains hydration, provides structural support, and facilitates cell signaling. Its length varies from oligomers to millions of daltons, with high (HMW-HA) and low (LMW-HA) molecular weight forms exhibiting different biological properties. HMW-HA promotes tissue homeostasis and has anti-inflammatory, antimetastatic effects, while LMW-HA is linked to inflammation, tissue injury, and metastasis (Gorbunova et al. 2020).
Naked mole rats (NMR) have a lifespan of up to 40 years, significantly longer than typical rats' 3-year lifespans, and exhibit cancer resistance, attributed to their abundant HMW-HA levels. A recent study shows that mice with the NMR hyaluronan synthase gene (NHAS2) experience fewer tumors, enhanced health, and a 10% longer lifespan.
Matrix Bio is working on creating an inhibitor for hyaluronidase 2, an enzyme responsible for breaking down hyaluronan. The goal of this inhibitor is to increase HMW-HA and decrease LMW-HA, thereby imitating NMR biology for humans.
1.4. Chondroitin sulfate
Chondroitin sulfate is an ECM proteoglycan. It is used as a supplement, in combination with glucosamine, to treat osteoarthritis and joint pain, and such usage has been linked to a reduction in all-cause mortality in humans (King and Xiang 2020). Additionally, chondroitin sulfate supplement and overexpression also increases lifespan in C. elegans and neuroplasticity in aged mice (Statzer et al. 2021, Yang et al. 2021).
Although chondroitin sulfate is available as a supplement, as in the case with collagen, its targeted delivery could present an opportunity to target age-related diseases caused by ECM stiffness.
1.5. TIMP2
Matrix metalloproteinases (MMPs) are enzymes that break down various components of the ECM. MMPs are inhibited by tissue inhibitors of metalloproteinases (TIMPs), and the balance between MMPs and TIMPs is critical for maintaining the integrity and function of the ECM.
During aging, there is a decrease in TIMPs and increase in MMPs, which lead to breakdown of ECM components. Adding TIMPs to counter this age-related effect therefore presents a valid strategy. In particular, TIMP2 has been found to revitalize the hippocampus and improve cognitive function in aged mice (Castellano et al. 2017).
No company is pursuing TIMP2 as a therapeutic target, presenting an unexplored opportunity.
2. Crosslinks breakdown or inhibition
Since the main cause of ECM stiffness is due to accumulation of crosslinks between molecules with slow turnovers, another therapeutic strategy is to inhibit crosslinks formation or break down the crosslinks.
2.1. Crosslinks inhibition
Several crosslinks inhibitors have been discovered and developed, including aminoguanidine, renin-an-giotensin system antagonists, pyridoxal 5′-phosphate and pyridoxal, hydralazine, and more (Fedintsev and Moskalev 2020). However, these inhibitors have not demonstrated any significant healthspan or lifespan benefits, as they are either ineffective at low concentrations or toxic at high concentrations.
Despite that, this is an active area for commercialization. Pratego is developing Amadorins, a type of inhibitor of AGE formation, for the treatment of Alzheimer's, diabetic peripheral neuropathy, and diabetic retinopathy. Isterian Biotech (a Cambrian portfolio company) is developing an inhibitor for TG2, a crosslinking enzyme, for idiopathic pulmonary fibrosis.
2.2. Crosslinks breakers
Another strategy is to break down the crosslinks. Lento Bio is developing a small molecule eyedrop to break down AGE in presbyopia. Revel Pharmaceuticals is developing a platform to discover enzymes to break down glucosepane, a type of AGE.
3. RAGE inhibition
RAGE (receptor for AGE) is a type of cell surface receptor that binds to AGEs and expressed in various types of cells. RAGE activation by AGEs has been implicated in the development and progression of several diseases, including diabetes, Alzheimer's disease, cardiovascular disease, and cancer, and its inhibition has shown promise in treating these aging-related diseases in preclinical models (Ramasamy et al. 2016).
RAGE Biotech is currently developing RAGE inhibitors for various age-related inflammatory conditions, including chronic lung, kidney, liver diseases and neurodegenerative diseases.
4. Mechanotransduction signaling
To mitigate the effects of ECM stiffness on cells, another strategy is to block the cells’ ability to sense the mechanical signals from the ECM, or the downstream effects of such signaling.
Inhibition of PIEZO1, a ion channel that responds to mechanotransduction, overrides mechanical signals in vivo and allows OPCs to maintain activity in the aging CNS (Segel et al. 2019). Selective inhibition of YAP/TAZ, transcriptional coactivators activated by ECM stiffness, in fibroblasts reverse fibrosis in mice (Haak et al. 2019).
Some companies are developing YAP/TAZ inhibitors for oncology, but not age-related diseases, and none are targeting PIEZO1. Thus exploring these targets could be a promising avenue for further investigation.